CaminapersName, GüellpersName (2017date). “The Neuroanatomical, Neurophysiological and Psychological Basis of Memory: Current Models and Their Origins.” Frontiers in Pharmacologytitle·j.
Object of study — the memoryterm·dom modelsterm current in the literature, classified and traced back to the developments that produced them
Research question — how the classificationsterm of memoryterm·dom now in use were arrived at, and which of them the scientific community currently accepts
Contribution — a three-level classificationterm - sensory, short-term and long-term memoryterm·dom - with each branch attributed to the study that introduced it, and a closing glossaryterm
phenomenon · claim-type · cross-domain-transfer · mechanism · claim-relation · replication-status · limitation — grounded in the full text| phenomenon | human memory systems — “The three major classifications of memory that the scientific community deals with today are as follows: sensory memory, short-term memory, and long-term memory.” | |
| claim-type | existence — “There are three main forms of memory: sensory memory, short-term memory, and long-term memory ( Figure 3 ).” | |
| method — evidence | — “This review aims to classify and clarify, from a neuroanatomical, neurophysiological, and psychological perspective, different memory models that are currently widespread in the literature as well as to describe their origins.” | |
| object of study — evidence | — “This review aims to classify and clarify, from a neuroanatomical, neurophysiological, and psychological perspective, different memory models that are currently widespread in the literature as well as to describe their origins. We believe it is important to consider previous developments without which one cannot adequately understand the kinds of models that are now current in the scientific literature. This article intends to provide a comprehensive and rigorous overview for understanding and ordering the latest scientific advances related to this subject.” | |
| research question — evidence | — “We believe it is important to consider previous developments without which one cannot adequately understand the classifications of memories and the kinds of memory models that are now current in the scientific literature.” | |
| contribution — evidence | — “There are three main forms of memory: sensory memory, short-term memory, and long-term memory ( Figure 3 ). Sensory memory refers to the retention of information coming from the senses. Short-term memory refers to information processed in a short period of time. Working memory performs this processing. Working memory consists of four elements that process information: the central executive (attention control), the visuospatial sketchpad (creates and maintains a visuospatial representation), the phonological buffer (stores and consolidates new words), and the episodic buffer (stores and integrates information from different sources). Long-term memory allows us to store information for long periods of time. This information may be retrieved consciously (explicit memory) or unconsciously (implicit memory). Explicit memory consists of episodic memory (time-related events) and semantic memory (concepts and meanings). Implicit memory has, in turn, procedural memory (motor and executive skills), associative memory (classical and operant conditioning), non-associative memory (sensitization and habituation), and priming (a primary stimulus influencing a secondary one).” | |
| transfer | from nineteenth-century philosophy and psychology: the primary and secondary memory distinction, carried into neuroscience under new names — “As Squire (2004) points out, the first theoretical approaches relevant to current neuroscience come from the 19th century. These include Maine de Biran (1804/1929) ( Maine de Biran, 1929 ) who, at the beginning of the century, wrote of mechanical memory, sensitive memory, and representative memory. The philosopher James, and his book The Principles of Psychology ( James, 1890 ), is also especially worth highlighting. Therein, James distinguishes between primary and secondary memory, thereby referring to short- and long-term memory, respectively.” | transfers[0] |
| transfer | from conditioning research: Pavlov's work, reclassified afterwards as the origin of associative memory — “The importance of Pavlov (1927) and Fitts and Posner (1967) are especially noteworthy during the first two thirds of the 20th century. Pavlov’s studies are related to a type of memory that later would be called associative memory. Meanwhile, Fitts and Posner’s studies are considered the first model to explain procedural memory.” | transfers[1] |
| transfer | from clinical neuropsychology: the amnesic patient as the instrument that separates memory types — “The experimental modern era arguably began when Milner (1962) demonstrated, with HM experiments, that a seriously ill patient could acquire a new skill (hand-eye coordination) without any memory of having encountered the task before. “While this finding showed that memory is not unitary, discussions at the time tended to set aside motor skills as a special case representing a less cognitive form of memory. The suggestion was that the rest of memory is of one piece and is dependent on medial temporal lobe structures” | transfers[2] |
| transfer | from medical genetics: two syndromes with opposite spared abilities, used as a natural double dissociation — “Wang and Bellugi (1994) presented a genetically based test that supports the functional and anatomical separation of Baddeley’s model with phonological and visuospatial storehouses. They compared two genetic syndromes (Williams and Down) with different brain morphology. Williams syndrome patients, despite having widespread mental handicaps, preserve their language skills, while Down syndrome patients preserve more partial capacities, but have very limited language skills. It was therefore assumed that the former would be better at verbal tasks related to operative memory, and that the latter would be better at visuospatial tasks related to operative memory. As expected, subjects with Williams syndrome performed better at phonological tasks, while subjects with Down syndrome, in turn, performed better at spatial tasks.” | transfers[3] |
| mechanism | habituation as progressive depletion of acetylcholine, which weakens the stimulus's effectiveness and so shrinks the motor response — “On one hand, for habituation, acetylcholine is progressively consumed, decreasing the effectiveness of the stimulus and thus the motor response.” | mechanisms[0] |
| mechanism | sensitization as serotonin released by a second sensory terminal producing an excess of acetylcholine and thus an amplified motor response — “Furthermore, for sensitization, the presence of serotonin, secreted by another sensory nerve terminal, causes an excess of acetylcholine.” | mechanisms[1] |
| mechanism | habituation as synaptic depression: repeated activation lowers the efficiency of synaptic transmission via a conductivity change in the stimulated neuron's membrane channels — “Thus, habituation is thought to be related to a decrease in the efficiency of synaptic transmission, a decrease that may be caused by a conductivity change in the membrane of the stimulated neuron’s iconic channels.” | mechanisms[2] |
| mechanism | memory systems are proposed to operate independently and in parallel, so one event can be laid down twice - as a declarative record and as a non-declarative one — “In the 90’s, a classification of the types of memory emerged, but the way they act and their interrelation was still unclear. In order to clarify its operation, Packard and McGaugh (1996) proposed that memory systems operate independently and in parallel. For example, an adverse event in childhood (e.g., seeing your grandfather being run over by a combine) can, on the one hand, consolidate as a stable declarative memory for the event itself (the sound of a combine always makes you remember that moment-episodic memory) and, on the other hand, can crystallize in non-declarative memory and result in a phobia experienced as a personality trait rather than as a mere memory (being near a combine will always produce panic and induces a desire to escape that situation-associative memory).” | mechanisms[3] |
| mechanism | the central executive controls attention, the phonological loop ensures retention of verbal information and the visuospatial sketchpad is responsible for storage visual and spatial information — “In general, we can say that the central executive controls attention, “the phonological loop ensures retention of verbal information and the visuospatial sketchpad is responsible for storage visual and spatial information” ( Grigorenko et al., 2012 ). The latter two sub-memory systems are equivalent to verbal and visual short-term memory systems, respectively.” | mechanisms[4] |
| mechanism | with a fourth component added twenty-six years later to hold information integrated from the other three — “Conceptual short-term memory/episodic buffer : This is a temporary storage system capable of integrating information from different sources that is probably controlled by the central executive. It is episodic in that it has episodes in which information is integrated through space and, potentially, extended through time.” | mechanisms[5] |
| mechanism | and long-term potentiation offered as the cellular substrate - brief synaptic activity producing a lasting increase in synaptic strength — “The research of the cellular and molecular substrates of memory has received much attention since Lomo (1966) described in the 60’s “a cellular model of experience-dependent plasticity—long-term potentiation (LTP)” ( Kandel et al., 2014 ). According to Lisman et al. (2012) : “LTP is a process whereby brief periods of synaptic activity can produce a long-lasting increase in the strength of a synapse, as shown by an increase in the size of the excitatory postsynaptic current.” | mechanisms[6] |
| builds-on | Baddeley and Hitch (1974) structural model of working memory — “Baddeley and Hitch’s structural model ( Baddeley and Hitch, 1974 ) were the most prominent; the latter is the most commonly accepted one today and thus we will focus on it in this article.” | claim_relations[0] |
| critiques | the modal model of short-term memory, whose prediction that longer residence favours transfer to long-term store was not borne out — “Despite the explanatory power of Atkinson and Shiffrin’s model, there were a number of issues that this model could not resolve, causing criticism of it. For example, this model implies that the longer an item remains in memory, the more likely it is to be transferred to long-term storage. But studies like those of Tulving and Pearlstone (1966) and Craik and Watkins (1973) show that said relationship does not exist.” | claim_relations[1] |
| qualifies | the pre-categorical characterisation of iconic memory, contradicted by better performance on letters and numbers than on meaningless forms — “Finally, regarding its pre-categorical nature, Sperling considered the information contained in this storehouse as physical information that maintains the raw data that is not related to the meaning of stimuli. Subsequently, evidence has been obtained that this system is not entirely pre-categorical ( Loftus et al., 1992 ) since the task improves when the stimuli to remember are letters or numbers instead of meaningless forms.” | claim_relations[2] |
| builds-on | the nineteenth-century distinction between primary and secondary memory, which the modern short-term and long-term terms replace — “As Squire (2004) points out, the first theoretical approaches relevant to current neuroscience come from the 19th century. These include Maine de Biran (1804/1929) ( Maine de Biran, 1929 ) who, at the beginning of the century, wrote of mechanical memory, sensitive memory, and representative memory. The philosopher James, and his book The Principles of Psychology ( James, 1890 ), is also especially worth highlighting. Therein, James distinguishes between primary and secondary memory, thereby referring to short- and long-term memory, respectively.” | claim_relations[3] |
| supports | the separation of the phonological and visuospatial stores, using two genetic syndromes with opposite preserved abilities — “Wang and Bellugi (1994) presented a genetically based test that supports the functional and anatomical separation of Baddeley’s model with phonological and visuospatial storehouses. They compared two genetic syndromes (Williams and Down) with different brain morphology. Williams syndrome patients, despite having widespread mental handicaps, preserve their language skills, while Down syndrome patients preserve more partial capacities, but have very limited language skills. It was therefore assumed that the former would be better at verbal tasks related to operative memory, and that the latter would be better at visuospatial tasks related to operative memory. As expected, subjects with Williams syndrome performed better at phonological tasks, while subjects with Down syndrome, in turn, performed better at spatial tasks.” | claim_relations[4] |
| supports | priming as a memory type of its own, by its survival in severe amnesia — “Several authors ( Tulving et al., 1982 ) had already mentioned the idea of priming as a separate type of memory, but it was not until the 90’s that experiments were conducted to show it ( Hamann and Squire, 1997 ; Stark and Squire, 2000 ; Levy et al., 2004 ). These studies show that severely amnesic patients can exhibit completely intact priming while performing memory tests that include conventional recognition of the same test items” | claim_relations[5] |
| reconciles | the coexistence of declarative and non-declarative traces of one event, by having the systems run independently and in parallel — “In the 90’s, a classification of the types of memory emerged, but the way they act and their interrelation was still unclear. In order to clarify its operation, Packard and McGaugh (1996) proposed that memory systems operate independently and in parallel. For example, an adverse event in childhood (e.g., seeing your grandfather being run over by a combine) can, on the one hand, consolidate as a stable declarative memory for the event itself (the sound of a combine always makes you remember that moment-episodic memory) and, on the other hand, can crystallize in non-declarative memory and result in a phobia experienced as a personality trait rather than as a mere memory (being near a combine will always produce panic and induces a desire to escape that situation-associative memory).” | claim_relations[6] |
| sense | A DEFINING CRITERION THAT SURVIVED ITS OWN REFUTATION: the pre-categorical nature is one of the three characteristics that define iconic memory, and evidence has since shown the system is NOT entirely pre-categorical — “Finally, regarding its pre-categorical nature, Sperling considered the information contained in this storehouse as physical information that maintains the raw data that is not related to the meaning of stimuli. Subsequently, evidence has been obtained that this system is not entirely pre-categorical ( Loftus et al., 1992 ) since the task improves when the stimuli to remember are letters or numbers instead of meaningless forms.” | senses[0] |
| sense | with the three characteristics - large capacity, short duration, pre-categorical nature - still given as the definition — “Subsequent research on visual persistence from Coltheart ( Coltheart, 1983 ) and Sperling’s studies ( Sperling, 1960 ) on the persistence of information led to the definition of three characteristics pertaining to iconic memory: a large capacity, a short duration, and a pre-categorical nature.” | senses[1] |
| sense | A CAPACITY THAT WAS NEVER OBSERVED, ONLY EXTRAPOLATED: subjects recalled three or four letters in the full report and about 75% of a cued row, and the large capacity follows by EXTRAPOLATING the partial report to the total — “Sperling (1960) demonstrated this large capacity after presenting the results of his total and partial reports. The full report consisted in presenting a 3 × 3 or 3 × 4 matrix of alphanumeric characters for a short period of time to subjects and later asking them which characters they remembered. On the other hand, in the partial report, subjects were directed to remember the characters in a row specifically assigned to them in the instructions. The total report’s results showed that subjects were only able to recall between 3 or 4 letters of the total number. However, in the partial report, subjects remembered around 75% of those that were asked. In extrapolating the partial report’s data to the total, it follows that individuals could report 9 of the 12 letters contained in the instructions (80% of the total), thus demonstrating a large capacity.” | senses[2] |
| sense | THE CLASS IS characterizeD BY ITS BEST-STUDIED MEMBER: research focused on iconic memory, the other two sensory types are comparatively scarce, and iconic memory is therefore presented as the paradigm of the class — “Scientific research has focused mainly on iconic memory; information on echoic and haptic memory is comparatively scarce. Thus, taking into account the goals of this article and that it is aimed at a higher education audience, presenting iconic memory as a paradigm of sensory memory is sufficient for an introductory overview.” | senses[3] |
| sense | ONE REFERENT, TWO NAMES, WRITTEN AS A PARENTHESIS: declarative memory (explicit) and non-declarative memory (implicit/procedural) — “In the 1980s, the differences between declarative and non-declarative memories were consolidated and disseminated. This, together with contributions from Tulving and others, such as Di Lollo or Graf and Schacter, enabled a more precise classification of different types of memory. To date, Di Lollo’s model of iconic memory ( Di Lollo, 1980 ) has been the most widely accepted and studied of the three existing types of sensory memory. As discussed in the next section, Di Lollo considered iconic memory a storage unit consisting of two components: the persistence of vision and information. Graf and Schacter (1985) proposed a general difference between declarative memory (explicit) and non-declarative memory (implicit/procedural). This stems from the distinction that Tulving (1972) proposed between the aforementioned episodic memory and semantic memory (both, as we will see, are currently included in declarative memory).” | senses[4] |
| sense | and the same pair again in the glossary heading itself - Explicit/declarative memory - so the slash IS the synonymy — “Explicit/declarative memory : refers to conscious memories of previously stored experiences, facts and concepts that are verifiable through a verbal reporting of them” | senses[5] |
| sense | and a third - Conceptual short-term memory/episodic buffer - for a component named twice in twenty-six years — “Conceptual short-term memory/episodic buffer : This is a temporary storage system capable of integrating information from different sources that is probably controlled by the central executive. It is episodic in that it has episodes in which information is integrated through space and, potentially, extended through time.” | senses[6] |
| sense | A DISTINCTION RENAMED ACROSS A CENTURY: James in 1890 distinguished primary from secondary memory, THEREBY REFERRING TO short- and long-term memory — “As Squire (2004) points out, the first theoretical approaches relevant to current neuroscience come from the 19th century. These include Maine de Biran (1804/1929) ( Maine de Biran, 1929 ) who, at the beginning of the century, wrote of mechanical memory, sensitive memory, and representative memory. The philosopher James, and his book The Principles of Psychology ( James, 1890 ), is also especially worth highlighting. Therein, James distinguishes between primary and secondary memory, thereby referring to short- and long-term memory, respectively.” | senses[7] |
| sense | and a type named retroactively - Pavlov's studies are related to a type of memory that LATER WOULD BE CALLED associative memory — “The importance of Pavlov (1927) and Fitts and Posner (1967) are especially noteworthy during the first two thirds of the 20th century. Pavlov’s studies are related to a type of memory that later would be called associative memory. Meanwhile, Fitts and Posner’s studies are considered the first model to explain procedural memory.” | senses[8] |
| sense | THE FIELD'S FIRST RESPONSE TO A FALSIFYING CASE WAS TO QUARANTINE IT: the patient learned a skill without remembering the task, and discussions at the time SET ASIDE motor skills as a special case, keeping the rest of memory of one piece — “The experimental modern era arguably began when Milner (1962) demonstrated, with HM experiments, that a seriously ill patient could acquire a new skill (hand-eye coordination) without any memory of having encountered the task before. “While this finding showed that memory is not unitary, discussions at the time tended to set aside motor skills as a special case representing a less cognitive form of memory. The suggestion was that the rest of memory is of one piece and is dependent on medial temporal lobe structures” | senses[9] |
| sense | A GLOSSARY THAT DISCLAIMS ITSELF: the commentary is NOT INTENDED AS AN EXHAUSTIVE DEFINITION, only enough to situate the reader in a complex panorama — “Finally, the following glossary includes commentary about the terminology that, in our opinion, is essential for an introductory overview, enabling interested students and professionals to effectively approach the latest memory-related discoveries. This commentary is not intended as an exhaustive definition, but rather collects relevant information to situate the reader within a complex panorama.” | senses[10] |
| sense | and the model that dominated short-term memory was criticised by a specific prediction that failed - that longer residence makes transfer to long-term storage more likely — “Despite the explanatory power of Atkinson and Shiffrin’s model, there were a number of issues that this model could not resolve, causing criticism of it. For example, this model implies that the longer an item remains in memory, the more likely it is to be transferred to long-term storage. But studies like those of Tulving and Pearlstone (1966) and Craik and Watkins (1973) show that said relationship does not exist.” | senses[11] |
| sense | A DOUBLE DISSOCIATION BORROWED FROM TWO GENETIC SYNDROMES: Williams patients keep language and Down patients keep more spatial capacity, and each does better on the matching task — “Wang and Bellugi (1994) presented a genetically based test that supports the functional and anatomical separation of Baddeley’s model with phonological and visuospatial storehouses. They compared two genetic syndromes (Williams and Down) with different brain morphology. Williams syndrome patients, despite having widespread mental handicaps, preserve their language skills, while Down syndrome patients preserve more partial capacities, but have very limited language skills. It was therefore assumed that the former would be better at verbal tasks related to operative memory, and that the latter would be better at visuospatial tasks related to operative memory. As expected, subjects with Williams syndrome performed better at phonological tasks, while subjects with Down syndrome, in turn, performed better at spatial tasks.” | senses[12] |
| sense | and the dissociation that made priming a separate type - severely amnesic patients show COMPLETELY INTACT priming on the same test items they cannot recognise — “Several authors ( Tulving et al., 1982 ) had already mentioned the idea of priming as a separate type of memory, but it was not until the 90’s that experiments were conducted to show it ( Hamann and Squire, 1997 ; Stark and Squire, 2000 ; Levy et al., 2004 ). These studies show that severely amnesic patients can exhibit completely intact priming while performing memory tests that include conventional recognition of the same test items” | senses[13] |
| sense | ONE EVENT LAID DOWN TWICE: the same childhood accident consolidates as a declarative memory of the event and crystallises separately as a phobia — “In the 90’s, a classification of the types of memory emerged, but the way they act and their interrelation was still unclear. In order to clarify its operation, Packard and McGaugh (1996) proposed that memory systems operate independently and in parallel. For example, an adverse event in childhood (e.g., seeing your grandfather being run over by a combine) can, on the one hand, consolidate as a stable declarative memory for the event itself (the sound of a combine always makes you remember that moment-episodic memory) and, on the other hand, can crystallize in non-declarative memory and result in a phobia experienced as a personality trait rather than as a mere memory (being near a combine will always produce panic and induces a desire to escape that situation-associative memory).” | senses[14] |
| differs in | the modal model of short-term memory, whose prediction that longer residence favours transfer to long-term store was not borne out — THE AXIS IS A SPECIFIC PREDICTION THAT FAILED. 'this model implies that the longer an item remains in memory, the more likely it is to be transferred to long-term storage. But studies...' The multi-store model is not rejected wholesale - one entailment is isolated and tested, so what survives and what does not are different parts of the same model. — “Despite the explanatory power of Atkinson and Shiffrin’s model, there were a number of issues that this model could not resolve, causing criticism of it. For example, this model implies that the longer an item remains in memory, the more likely it is to be transferred to long-term storage. But studies like those of Tulving and Pearlstone (1966) and Craik and Watkins (1973) show that said relationship does not exist.” — “this model implies that the longer an item remains in memory, the more likely it is to be transferred to long-term storage” | claim_relations[1] |
| differs in | the pre-categorical characterisation of iconic memory, contradicted by better performance on letters and numbers than on meaningless forms — THE AXIS IS WHETHER THE STORE IS SENSITIVE TO MEANING. Sperling 'considered the information contained in this storehouse as physical information that maintains the raw data that is not related to the meaning of stimuli. Subsequently, evidence has been obtained that this...' The pre-categorical characterisation is qualified on the one property that defines it. — “Finally, regarding its pre-categorical nature, Sperling considered the information contained in this storehouse as physical information that maintains the raw data that is not related to the meaning of stimuli. Subsequently, evidence has been obtained that this system is not entirely pre-categorical ( Loftus et al., 1992 ) since the task improves when the stimuli to remember are letters or numbers instead of meaningless forms.” — “physical information that maintains the raw data that is not related to the meaning of stimuli” | claim_relations[2] |
| note | short-term memory —distinct-from→ long-term memory — kept as independent even by the account that emphasised processing over structure — “As an introduction, it can be argued that Craik and Lockhart (1972) understood memory not as a process through which information is deepened at higher levels until it becomes part of long-term memory, but rather as a system of storehouses. Despite an emphasis on information processing (instead of structure), they continued to accept the existence of short-term memory as independent from long-term memory. For their part, Baddeley and Hitch’s proposal ( Baddeley and Hitch, 1974 ) contemplated a multi-component working memory instead of a storage unit in the short term.” | concept_edges[38] |
| edge | Williams —contrasted-with→ Down — “Wang and Bellugi (1994) presented a genetically based test that supports the functional and anatomical separation of Baddeley’s model with phonological and visuospatial storehouses. They compared two genetic syndromes (Williams and Down) with different brain morphology. Williams syndrome patients, despite having widespread mental handicaps, preserve their language skills, while Down syndrome patients preserve more partial capacities, but have very limited language skills. It was therefore assumed that the former would be better at verbal tasks related to operative memory, and that the latter would be better at visuospatial tasks related to operative memory. As expected, subjects with Williams syndrome performed better at phonological tasks, while subjects with Down syndrome, in turn, performed better at spatial tasks.” | concept_edges[46] |
| note | episodic buffer —same-as→ short-term memory — the glossary entry is headed with both names at once - Conceptual short-term memory/episodic buffer — “Conceptual short-term memory/episodic buffer : This is a temporary storage system capable of integrating information from different sources that is probably controlled by the central executive. It is episodic in that it has episodes in which information is integrated through space and, potentially, extended through time.” | concept_edges[64] |
| for which use | limitation — the molecular level of the account: IN THIS ARTICLE WE CAN ONLY POINT OUT GENERAL TRAITS — “Although knowledge of molecular mechanisms is important for constructing a complete vision of memory models, in this article we can only point out general traits as summarized in this introduction” | limitations[0] |
| for which use | limitation — the treatment of sensory memory: PRESENTING ICONIC MEMORY AS A PARADIGM OF SENSORY MEMORY IS SUFFICIENT FOR AN INTRODUCTORY OVERVIEW, given the article's audience — “Thus, taking into account the goals of this article and that it is aimed at a higher education audience, presenting iconic memory as a paradigm of sensory memory is sufficient for an introductory overview.” | limitations[1] |
| for which use | limitation — the glossary definitions: THIS COMMENTARY IS NOT INTENDED AS AN EXHAUSTIVE DEFINITION, BUT RATHER COLLECTS RELEVANT INFORMATION TO SITUATE THE READER — “This commentary is not intended as an exhaustive definition, but rather collects relevant information to situate the reader within a complex panorama.” | limitations[2] |
| for which use | limitation — any claim about sensory memory as a whole: SCIENTIFIC RESEARCH HAS FOCUSED MAINLY ON ICONIC MEMORY; INFORMATION ON ECHOIC AND HAPTIC MEMORY IS COMPARATIVELY SCARCE — “Scientific research has focused mainly on iconic memory; information on echoic and haptic memory is comparatively scarce.” | limitations[3] |
| for which use | limitation — the definitions the glossary supplies: the commentary is what IS ESSENTIAL FOR AN INTRODUCTORY OVERVIEW, ENABLING INTERESTED STUDENTS AND PROFESSIONALS TO EFFECTIVELY APPROACH THE LATEST MEMORY-RELATED DISCOVERIES - not an exhaustive definition — “Finally, the following glossary includes commentary about the terminology that, in our opinion, is essential for an introductory overview, enabling interested students and professionals to effectively approach the latest memory-related discoveries. This commentary is not intended as an exhaustive definition, but rather collects relevant information to situate the reader within a complex panorama.” | limitations[4] |
| for which use | limitation — the mechanistic completeness of the account: ALTHOUGH KNOWLEDGE OF MOLECULAR MECHANISMS IS IMPORTANT FOR CONSTRUCTING A COMPLETE VISION OF MEMORY MODELS, IN THIS ARTICLE WE CAN ONLY POINT OUT GENERAL TRAITS — “Although knowledge of molecular mechanisms is important for constructing a complete vision of memory models, in this article we can only point out general traits as summarized in this introduction [for more information see ( Kandel et al., 2014 )]. In addition, knowledge gained from neuroimaging studies ( Binder and Desai, 2011 ), as well as knowledge of the neural markers associated with memory ( Meneses, 2015 ), will likely play a key role in future models of memory mechanisms, but in this review, as stated above, we focus mainly on neuroanatomical, neurophysiological, and psychological mechanisms.” | limitations[5] |
| for which use | limitation — any claim about sensory memory as a whole: SCIENTIFIC RESEARCH HAS FOCUSED MAINLY ON ICONIC MEMORY; INFORMATION ON ECHOIC AND HAPTIC MEMORY IS COMPARATIVELY SCARCE — “Scientific research has focused mainly on iconic memory; information on echoic and haptic memory is comparatively scarce. Thus, taking into account the goals of this article and that it is aimed at a higher education audience, presenting iconic memory as a paradigm of sensory memory is sufficient for an introductory overview.” | limitations[6] |
| for which use | limitation — the pre-categorical characteristic that partly defines the construct: Sperling treated it as PHYSICAL INFORMATION THAT MAINTAINS THE RAW DATA THAT IS NOT RELATED TO THE MEANING OF STIMULI, and SUBSEQUENTLY, EVIDENCE HAS BEEN OBTAINED THAT contradicts this — “Finally, regarding its pre-categorical nature, Sperling considered the information contained in this storehouse as physical information that maintains the raw data that is not related to the meaning of stimuli. Subsequently, evidence has been obtained that this system is not entirely pre-categorical ( Loftus et al., 1992 ) since the task improves when the stimuli to remember are letters or numbers instead of meaningless forms.” | limitations[7] |
| evidential status | mechanism — the paper's own words: is thought to be — “Thus, habituation is thought to be related to a decrease in the efficiency of synaptic transmission, a decrease that may be caused by a conductivity change in the membrane of the stimulated neuron’s iconic channels.” | mechanisms[2] |
| replication | untested | |
| limitation | Molecular mechanisms of memory are deliberately treated only in outline, so the account is not a complete picture of memory. — “Although knowledge of molecular mechanisms is important for constructing a complete vision of memory models, in this article we can only point out general traits as summarized in this introduction” | limitations[0] |
| limitation | Sensory memory is covered through iconic memory alone, which the authors justify by the article's introductory purpose rather than by evidential completeness. — “Thus, taking into account the goals of this article and that it is aimed at a higher education audience, presenting iconic memory as a paradigm of sensory memory is sufficient for an introductory overview.” | limitations[1] |
| limitation | The glossary definitions are explicitly non-exhaustive. — “This commentary is not intended as an exhaustive definition, but rather collects relevant information to situate the reader within a complex panorama.” | limitations[2] |
| limitation | Coverage of the other two sensory-memory types is constrained by how little research exists on them. — “Scientific research has focused mainly on iconic memory; information on echoic and haptic memory is comparatively scarce.” | limitations[3] |
| limitation | the glossary is explicitly not intended as an exhaustive definition, only as enough to situate a reader — “Finally, the following glossary includes commentary about the terminology that, in our opinion, is essential for an introductory overview, enabling interested students and professionals to effectively approach the latest memory-related discoveries. This commentary is not intended as an exhaustive definition, but rather collects relevant information to situate the reader within a complex panorama.” | limitations[4] |
| limitation | molecular mechanisms are acknowledged as necessary for a complete picture and only pointed at in general traits — “Although knowledge of molecular mechanisms is important for constructing a complete vision of memory models, in this article we can only point out general traits as summarized in this introduction [for more information see ( Kandel et al., 2014 )]. In addition, knowledge gained from neuroimaging studies ( Binder and Desai, 2011 ), as well as knowledge of the neural markers associated with memory ( Meneses, 2015 ), will likely play a key role in future models of memory mechanisms, but in this review, as stated above, we focus mainly on neuroanatomical, neurophysiological, and psychological mechanisms.” | limitations[5] |
| limitation | scientific research has focused mainly on iconic memory, information on echoic and haptic memory is comparatively scarce, and presenting iconic memory as a paradigm of sensory memory is treated as sufficient — “Scientific research has focused mainly on iconic memory; information on echoic and haptic memory is comparatively scarce. Thus, taking into account the goals of this article and that it is aimed at a higher education audience, presenting iconic memory as a paradigm of sensory memory is sufficient for an introductory overview.” | limitations[6] |
| limitation | and one of the three defining characteristics of that subtype has been contradicted by later evidence — “Finally, regarding its pre-categorical nature, Sperling considered the information contained in this storehouse as physical information that maintains the raw data that is not related to the meaning of stimuli. Subsequently, evidence has been obtained that this system is not entirely pre-categorical ( Loftus et al., 1992 ) since the task improves when the stimuli to remember are letters or numbers instead of meaningless forms.” | limitations[7] |
finding · quantity · variable · definition · key-term — grounded in the full text| finding | The review settles on a three-way top-level taxonomy of memory as the currently consensual classification. — “The three major classifications of memory that the scientific community deals with today are as follows: sensory memory, short-term memory, and long-term memory.” | content_tags.findings[0] |
| finding | Working memory is presented as a four-component system rather than a single short-term store. — “Working memory consists of four elements that process information: the central executive (attention control), the visuospatial sketchpad (creates and maintains a visuospatial representation), the phonological buffer (stores and consolidates new words), and the episodic buffer (stores and integrates information from different sources).” | content_tags.findings[1] |
| finding | Implicit memory is subdivided into exactly four kinds, with priming counted as one of them. — “There are four types of implicit memory, including procedural, associative, non-associative, and priming.” | content_tags.findings[2] |
| finding | Among competing short-term memory models the review judges Baddeley and Hitch's structural model to be the one most widely accepted today, and adopts it as its framework. — “Craik and Lockhart’s process model ( Craik and Lockhart, 1972 ) and Baddeley and Hitch’s structural model ( Baddeley and Hitch, 1974 ) were the most prominent; the latter is the most commonly accepted one today and thus we will focus on it in this article.” | content_tags.findings[3] |
| finding | For sensory memory the review identifies Di Lollo's two-component account as the dominant model of iconic memory. — “Di Lollo’s model ( Di Lollo, 1980 ) is the most widely accepted model of iconic memory.” | content_tags.findings[4] |
| finding | Research has concentrated on iconic memory, with comparatively little known about echoic and haptic memory. — “Scientific research has focused mainly on iconic memory; information on echoic and haptic memory is comparatively scarce.” | content_tags.findings[5] |
| finding | the review aims to classify and clarify different memory models that are currently widespread in the literature as well as to describe their origins — “This review aims to classify and clarify, from a neuroanatomical, neurophysiological, and psychological perspective, different memory models that are currently widespread in the literature as well as to describe their origins. We believe it is important to consider previous developments without which one cannot adequately understand the kinds of models that are now current in the scientific literature. This article intends to provide a comprehensive and rigorous overview for understanding and ordering the latest scientific advances related to this subject.” | content_tags.findings[6] |
| finding | three major classifications are current - sensory, short-term and long-term memory - with the last split by whether retrieval is conscious — “The three major classifications of memory that the scientific community deals with today are as follows: sensory memory, short-term memory, and long-term memory. Information from the world around us begins to be stored by sensory memory, making it possible for this information to be accessible in the future. Short-term memory refers to the information processed by the individual in a short period of time. Working memory performs this processing. Long-term memory allows us to store information for long periods of time. This information may be retrieved consciously (explicit memory) or unconsciously (implicit memory).” | content_tags.findings[7] |
| finding | with the scope narrowed twice and said so - molecular mechanisms only in general traits, neuroimaging left to future models — “Although knowledge of molecular mechanisms is important for constructing a complete vision of memory models, in this article we can only point out general traits as summarized in this introduction [for more information see ( Kandel et al., 2014 )]. In addition, knowledge gained from neuroimaging studies ( Binder and Desai, 2011 ), as well as knowledge of the neural markers associated with memory ( Meneses, 2015 ), will likely play a key role in future models of memory mechanisms, but in this review, as stated above, we focus mainly on neuroanatomical, neurophysiological, and psychological mechanisms.” | content_tags.findings[8] |
| finding | and the previous developments held to be necessary for understanding the current classification at all — “We believe it is important to consider previous developments without which one cannot adequately understand the classifications of memories and the kinds of memory models that are now current in the scientific literature.” | content_tags.findings[9] |
| finding | A DISTINCTION RENAMED ACROSS A CENTURY: James in 1890 wrote of primary and secondary memory, THEREBY REFERRING TO short- and long-term memory — “As Squire (2004) points out, the first theoretical approaches relevant to current neuroscience come from the 19th century. These include Maine de Biran (1804/1929) ( Maine de Biran, 1929 ) who, at the beginning of the century, wrote of mechanical memory, sensitive memory, and representative memory. The philosopher James, and his book The Principles of Psychology ( James, 1890 ), is also especially worth highlighting. Therein, James distinguishes between primary and secondary memory, thereby referring to short- and long-term memory, respectively.” | content_tags.findings[10] |
| finding | and a type named retroactively - Pavlov's studies relate to a type of memory that LATER WOULD BE CALLED associative — “The importance of Pavlov (1927) and Fitts and Posner (1967) are especially noteworthy during the first two thirds of the 20th century. Pavlov’s studies are related to a type of memory that later would be called associative memory. Meanwhile, Fitts and Posner’s studies are considered the first model to explain procedural memory.” | content_tags.findings[11] |
| finding | the pre-1960s systematisations already separated a mechanical skill-acquiring memory, on philosophical grounds — “Prior to the 60’s, most systematizations of memory distinguished a more mechanical type of memory related to the acquisition of skills, which is, in turn, related to activity of the intellect. Unlike what followed, debates in this period were mainly philosophical or based on psychological intuition” | content_tags.findings[12] |
| finding | after Milner's finding showed memory is not unitary, discussions set motor skills aside as a special case and treated the rest of memory as one piece — “The experimental modern era arguably began when Milner (1962) demonstrated, with HM experiments, that a seriously ill patient could acquire a new skill (hand-eye coordination) without any memory of having encountered the task before. “While this finding showed that memory is not unitary, discussions at the time tended to set aside motor skills as a special case representing a less cognitive form of memory. The suggestion was that the rest of memory is of one piece and is dependent on medial temporal lobe structures” [ATTRIBUTED TO A CITED AUTHOR, NOT THIS PAPER] the paper’s own words: “Milner (1962) demonstrated” | content_tags.findings[13] |
| finding | the episodic and semantic split arrives in 1972, and the fourth working memory component in 2000 — “In the seventies, Tulving, Baddeley, and Hitch and Kandel’s investigations are especially noteworthy. Tulving (1972) first proposed the distinction between episodic memory and semantic memory. Baddeley and Hitch (1974) conducted research on the components of working memory. Both authors considered working memory as a limited capacity system that allows temporary storage and manipulation of information necessary to perform complex tasks such as understanding, learning, and reasoning. As explained later on, at first (1974), they proposed the existence of three subsystems within the multi-storehouse model of short-term memory: the central executive, a phonological or articulatory loop and a visuospatial sketchpad. Later, Baddeley (2000) included a fourth subsystem, the episodic buffer, which combines information from the subsystems in a form of temporal representation.” | content_tags.findings[14] |
| finding | ONE REFERENT, TWO NAMES, WRITTEN AS A PARENTHESIS: declarative memory (explicit) and non-declarative memory (implicit/procedural) — “In the 1980s, the differences between declarative and non-declarative memories were consolidated and disseminated. This, together with contributions from Tulving and others, such as Di Lollo or Graf and Schacter, enabled a more precise classification of different types of memory. To date, Di Lollo’s model of iconic memory ( Di Lollo, 1980 ) has been the most widely accepted and studied of the three existing types of sensory memory. As discussed in the next section, Di Lollo considered iconic memory a storage unit consisting of two components: the persistence of vision and information. Graf and Schacter (1985) proposed a general difference between declarative memory (explicit) and non-declarative memory (implicit/procedural). This stems from the distinction that Tulving (1972) proposed between the aforementioned episodic memory and semantic memory (both, as we will see, are currently included in declarative memory).” | content_tags.findings[15] |
| finding | ONE EVENT LAID DOWN TWICE: the same childhood accident becomes a declarative memory and a phobia, on systems that run independently and in parallel — “In the 90’s, a classification of the types of memory emerged, but the way they act and their interrelation was still unclear. In order to clarify its operation, Packard and McGaugh (1996) proposed that memory systems operate independently and in parallel. For example, an adverse event in childhood (e.g., seeing your grandfather being run over by a combine) can, on the one hand, consolidate as a stable declarative memory for the event itself (the sound of a combine always makes you remember that moment-episodic memory) and, on the other hand, can crystallize in non-declarative memory and result in a phobia experienced as a personality trait rather than as a mere memory (being near a combine will always produce panic and induces a desire to escape that situation-associative memory).” [ATTRIBUTED TO A CITED AUTHOR, NOT THIS PAPER] the paper’s own words: “Packard and McGaugh (1996) proposed” | content_tags.findings[16] |
| finding | THE DISSOCIATION THAT MADE PRIMING A TYPE: severely amnesic patients show completely intact priming on the same items they cannot recognise — “Several authors ( Tulving et al., 1982 ) had already mentioned the idea of priming as a separate type of memory, but it was not until the 90’s that experiments were conducted to show it ( Hamann and Squire, 1997 ; Stark and Squire, 2000 ; Levy et al., 2004 ). These studies show that severely amnesic patients can exhibit completely intact priming while performing memory tests that include conventional recognition of the same test items” [ATTRIBUTED TO AN INDEFINITE CITED STUDY, NOT THIS PAPER] the paper’s own words: “studies show” | content_tags.findings[17] |
| finding | three sensory types are named - iconic, echoic and haptic - one per modality — ““Sensory memory is the capacity for briefly retaining the large amounts of information that people encounter daily” ( Siegler and Alibali, 2005 ). There are three types of sensory memory: echoic memory, iconic memory, and haptic memory. Iconic memory retains information that is gathered through sight, echoic memory retains information gathered through auditory stimuli and haptic memory retains data acquired through touch.” | content_tags.findings[18] |
| finding | THE CLASS IS characterizeD BY ITS BEST-STUDIED MEMBER: the other two are comparatively scarce, so iconic memory stands in as the paradigm — “Scientific research has focused mainly on iconic memory; information on echoic and haptic memory is comparatively scarce. Thus, taking into account the goals of this article and that it is aimed at a higher education audience, presenting iconic memory as a paradigm of sensory memory is sufficient for an introductory overview.” | content_tags.findings[19] |
| finding | and the accepted model of it has two components, the persistence of vision and of information — “Di Lollo’s model ( Di Lollo, 1980 ) is the most widely accepted model of iconic memory. Therein, he considered iconic memory a storehouse constituted by two components: the persistence of vision and information.” | content_tags.findings[20] |
| finding | three characteristics are given AS the definition - large capacity, short duration, pre-categorical nature — “Subsequent research on visual persistence from Coltheart ( Coltheart, 1983 ) and Sperling’s studies ( Sperling, 1960 ) on the persistence of information led to the definition of three characteristics pertaining to iconic memory: a large capacity, a short duration, and a pre-categorical nature.” | content_tags.findings[21] |
| finding | the large capacity was inferred by extrapolation: subjects recalled 3 or 4 letters in the full report, and scaling up the partial report implies about 9 of 12 — “Sperling (1960) demonstrated this large capacity after presenting the results of his total and partial reports. The full report consisted in presenting a 3 × 3 or 3 × 4 matrix of alphanumeric characters for a short period of time to subjects and later asking them which characters they remembered. On the other hand, in the partial report, subjects were directed to remember the characters in a row specifically assigned to them in the instructions. The total report’s results showed that subjects were only able to recall between 3 or 4 letters of the total number. However, in the partial report, subjects remembered around 75% of those that were asked. In extrapolating the partial report’s data to the total, it follows that individuals could report 9 of the 12 letters contained in the instructions (80% of the total), thus demonstrating a large capacity.” [ATTRIBUTED TO A CITED AUTHOR, NOT THIS PAPER] the paper’s own words: “Sperling (1960) demonstrated” | content_tags.findings[22] |
| finding | with a second laboratory corroborating the short duration by delaying the cue — “Averbach and Coriell’s experiments ( Averbach and Coriell, 1961 ) corroborated Sperling’s conclusion; they presented a variety of letters for a certain period of time to the subject. After each letter, and in the same position, they showed a particular visual sign. The participant’s task was to name the letter that occupied the position of the visual sign. When the visual sign appeared immediately after the letters, participants could correctly name the letter that occupied the position of the sign, however, as the presentation of the sign became more delayed, participant performance worsened. These results also show the rapid decline of visual information.” | content_tags.findings[23] |
| finding | later evidence showed the store is not entirely pre-categorical, since performance improves for letters and numbers over meaningless forms — “Finally, regarding its pre-categorical nature, Sperling considered the information contained in this storehouse as physical information that maintains the raw data that is not related to the meaning of stimuli. Subsequently, evidence has been obtained that this system is not entirely pre-categorical ( Loftus et al., 1992 ) since the task improves when the stimuli to remember are letters or numbers instead of meaningless forms.” | content_tags.findings[24] |
| finding | one criticised implication of the modal model - that longer residence makes transfer to long-term storage more likely - is contradicted by two studies — “Despite the explanatory power of Atkinson and Shiffrin’s model, there were a number of issues that this model could not resolve, causing criticism of it. For example, this model implies that the longer an item remains in memory, the more likely it is to be transferred to long-term storage. But studies like those of Tulving and Pearlstone (1966) and Craik and Watkins (1973) show that said relationship does not exist.” [ATTRIBUTED TO A CITED AUTHOR, NOT THIS PAPER] the paper’s own words: “Craik and Watkins (1973) show” | content_tags.findings[25] |
| finding | with several successor models listed and one chosen as the most commonly accepted today — “Given these criticisms, new models began to appear to explain memory, such as those from Cowan (1988 , 1995 , 1999 ) and Goldman-Rakic (1995) . Among them, Craik and Lockhart’s process model ( Craik and Lockhart, 1972 ) and Baddeley and Hitch’s structural model ( Baddeley and Hitch, 1974 ) were the most prominent; the latter is the most commonly accepted one today and thus we will focus on it in this article.” | content_tags.findings[26] |
| finding | the short-term store is kept independent of the long-term one even by the account that emphasised processing over structure — “As an introduction, it can be argued that Craik and Lockhart (1972) understood memory not as a process through which information is deepened at higher levels until it becomes part of long-term memory, but rather as a system of storehouses. Despite an emphasis on information processing (instead of structure), they continued to accept the existence of short-term memory as independent from long-term memory. For their part, Baddeley and Hitch’s proposal ( Baddeley and Hitch, 1974 ) contemplated a multi-component working memory instead of a storage unit in the short term.” | content_tags.findings[27] |
| finding | working memory is defined as temporary storage AND manipulation, for comprehension, learning and reasoning — ““The term working memory refers to a brain system that provides temporary storage and manipulation of the information necessary for such complex cognitive tasks as language comprehension, learning and reasoning” ( Baddeley, 1992 ). At first (1974), they proposed the existence of three subsystems within the multi-storehouse model of short-term memory: the central executive, a phonological or articulatory loop and a visuospatial sketchpad.” | content_tags.findings[28] |
| finding | and its two stores are declared equivalent to the verbal and visual short-term memory systems — “In general, we can say that the central executive controls attention, “the phonological loop ensures retention of verbal information and the visuospatial sketchpad is responsible for storage visual and spatial information” ( Grigorenko et al., 2012 ). The latter two sub-memory systems are equivalent to verbal and visual short-term memory systems, respectively.” | content_tags.findings[29] |
| finding | A DOUBLE DISSOCIATION BORROWED FROM MEDICAL GENETICS, with the expectation stated in advance and then met — “Wang and Bellugi (1994) presented a genetically based test that supports the functional and anatomical separation of Baddeley’s model with phonological and visuospatial storehouses. They compared two genetic syndromes (Williams and Down) with different brain morphology. Williams syndrome patients, despite having widespread mental handicaps, preserve their language skills, while Down syndrome patients preserve more partial capacities, but have very limited language skills. It was therefore assumed that the former would be better at verbal tasks related to operative memory, and that the latter would be better at visuospatial tasks related to operative memory. As expected, subjects with Williams syndrome performed better at phonological tasks, while subjects with Down syndrome, in turn, performed better at spatial tasks.” | content_tags.findings[30] |
| finding | priming is defined as exposure to a stimulus influencing the response to a later one, surviving the loss of conscious recollection — “Priming, the fourth modality of non-declarative or implicit memory, is an effect whereby exposure to certain stimuli influences the response given to stimuli presented later. An example is in order. If you present a list of words to a person that contains the word ‘ball,’ and then the person is asked to participate in a task to complete words, they are more likely to respond with the word ball to the presentation of the word bowl than if they had not previously seen that word in the original list. Thus, the priming capacity can affect the choice of a particular word on a test to complete words, even long after conscious recollection of the primed words has been forgotten.” | content_tags.findings[31] |
| finding | with a second worked example in picture identification from fragments — “Another context where this can be seen is in asking a participant to identify an image from a small fragment. The participant is shown a larger portion of the image over time, giving them the ability to identify the image at the end. The participant will take longer to identify the image if it is the first time he/she sees it. But if he/she already saw it in a previous trial, he/she takes less time” | content_tags.findings[32] |
| finding | long-term potentiation is described from the start as a cellular MODEL of experience-dependent plasticity — “The research of the cellular and molecular substrates of memory has received much attention since Lomo (1966) described in the 60’s “a cellular model of experience-dependent plasticity—long-term potentiation (LTP)” ( Kandel et al., 2014 ). According to Lisman et al. (2012) : “LTP is a process whereby brief periods of synaptic activity can produce a long-lasting increase in the strength of a synapse, as shown by an increase in the size of the excitatory postsynaptic current.” | content_tags.findings[33] |
| finding | and the asymmetry disclosed - the processes that establish it are well characterized, its decay is poorly understood — “Many of these questions have to do with molecular processes of memory consolidation, retrieval, and decay. Take, for instance, the processes underlying the LTP of synaptic strength among neurons of the hippocampus ( Dong et al., 2015 ). In their review, Hardt et al. (2013) point out that while the “molecular processes involved in establishing LTP have been characterized well, the decay of early and late LTP is poorly understood.” One possibility that has recently been suggested is that LTP decay is mediated by AMPAR endocytosis, which in turn implies that inhibition of this process could preserve LTP and help to prevent memory loss” | content_tags.findings[34] |
| finding | retrieval DESTABILISES what it recovers, so the same protein synthesis is needed again — “Also requiring further investigation are the molecular processes involved in the regulation of protein synthesis related to memory. It is now thought that protein synthesis is not only involved in the consolidation of new memories, but must also be used to re-consolidate memories that have been degraded or “destabilized” as a result of retrieval.” | content_tags.findings[35] |
| finding | Hebbian strengthening is judged important but not sufficient, with anti-Hebbian mechanisms found alongside it — “Another set of important questions relates to the long-standing hypothesis of “Hebbian learning”—the strengthening of synapses between neurons with correlated activity—and its role in memory. At the same time that we are learning more about the mechanisms involved in Hebbian plasticity, we are also learning about how these mechanisms are complemented by synaptogenesis and neuromodulatory processes. Recent research has shown that synaptogenesis is not only important during development, but also plays a central role in associative learning and memory. Synaptogenesis can be triggered by neuron–astrocyte or neuron–neuron contact, and mediated by cell-adhesion proteins including neurexin/neuroligin, Eph receptors, and cadherins, which activate intracellular signaling pathways involving cofilin, GTPases, and other proteins (for a review see Nelson and Alkon, 2015 ). Others have proposed that Hebbian processes, while important, are not sufficient for memory formation, and must be supported by the activation of neuromodulatory processes, especially in the case of associative aversive learning ( Johansen et al., 2014 ). Another study found evidence for both Hebbian and anti-Hebbian mechanisms of synaptic plasticity, indicating that the mechanisms of learning are highly adaptable” | content_tags.findings[36] |
| finding | and previously inconsequential information can be strengthened RETROACTIVELY by a later emotional experience — “Finally, other questions relate to the special role of the amygdala in the emotional enhancement of memory consolidation. It has long been known that emotional arousal contributes to the selection and consolidation of memory. It has also been shown that previously weak or inconsequential information can be strengthened retroactively through an emotional learning experience ( Dunsmoor et al., 2015 ). Evidence suggests that it is the amygdala that is most responsible for the enhancement of memory ( de Voogd et al., 2016 ). As suggested by a review, these developments “will likely lead to an updated view of the amygdala as a critical nexus within large-scale networks supporting different aspects of memory processing for emotionally arousing experiences” | content_tags.findings[37] |
| finding | the whole classification is restated in one paragraph at the end, four implicit types and two explicit ones — “There are three main forms of memory: sensory memory, short-term memory, and long-term memory ( Figure 3 ). Sensory memory refers to the retention of information coming from the senses. Short-term memory refers to information processed in a short period of time. Working memory performs this processing. Working memory consists of four elements that process information: the central executive (attention control), the visuospatial sketchpad (creates and maintains a visuospatial representation), the phonological buffer (stores and consolidates new words), and the episodic buffer (stores and integrates information from different sources). Long-term memory allows us to store information for long periods of time. This information may be retrieved consciously (explicit memory) or unconsciously (implicit memory). Explicit memory consists of episodic memory (time-related events) and semantic memory (concepts and meanings). Implicit memory has, in turn, procedural memory (motor and executive skills), associative memory (classical and operant conditioning), non-associative memory (sensitization and habituation), and priming (a primary stimulus influencing a secondary one).” | content_tags.findings[38] |
| finding | A GLOSSARY THAT DISCLAIMS ITSELF: not intended as an exhaustive definition, only enough to situate a reader in a complex panorama — “Finally, the following glossary includes commentary about the terminology that, in our opinion, is essential for an introductory overview, enabling interested students and professionals to effectively approach the latest memory-related discoveries. This commentary is not intended as an exhaustive definition, but rather collects relevant information to situate the reader within a complex panorama.” | content_tags.findings[39] |
| finding | with associative memory defined through its two conditioning procedures rather than its content — “Associative memory : refers to the storage and retrieval of information resulting from an association (i.e., resulting from an association with other information). Two types of conditioning are involved in its acquisition: classical conditioning and operant conditioning. Classical conditioning is a kind of associative learning between stimuli and behavior, and operant conditioning is a form of learning in which new behaviors develop in terms of their consequences.” | content_tags.findings[40] |
| finding | episodic memory defined by what it includes - time, place and detail of a unique personal experience — “Episodic memory : “involves the ability to learn, store, and retrieve information about unique personal experiences that occur in daily life. These memories typically include information about the time and place of an event, as well as detailed information about the event itself” | content_tags.findings[41] |
| finding | AND THE TEST IS INSIDE THE DEFINITION: explicit memories are those verifiable through a verbal reporting of them — “Explicit/declarative memory : refers to conscious memories of previously stored experiences, facts and concepts that are verifiable through a verbal reporting of them” | content_tags.findings[42] |
| finding | and one glossary entry is headed with both of its names at once — “Conceptual short-term memory/episodic buffer : This is a temporary storage system capable of integrating information from different sources that is probably controlled by the central executive. It is episodic in that it has episodes in which information is integrated through space and, potentially, extended through time.” | content_tags.findings[43] |
| quantity | 100 and 300 ms — duration of the pre-categorical visual representation (persistence of vision component of iconic memory) — “Iconic memory corresponds to the pre-categorical representation image/visual that remains between 100 and 300 ms.” | content_tags.quantities[0] |
| quantity | 800 ms — duration of the post-categorical persistence-of-information component of iconic memory — “Iconic memory is a storehouse of information that lasts 800 ms and that represents a codified and already categorized version of the visual image.” | content_tags.quantities[1] |
| quantity | 1 s — approximate overall retention time of iconic memory — “Iconic memory retains information from the sense of sight with an approximate duration of 1 s.” | content_tags.quantities[2] |
| quantity | 3 or 4 letters — number of characters recalled in Sperling's full-report condition — “The total report’s results showed that subjects were only able to recall between 3 or 4 letters of the total number.” | content_tags.quantities[3] |
| quantity | 75% — proportion of the cued row recalled in Sperling's partial-report condition — “However, in the partial report, subjects remembered around 75% of those that were asked.” | content_tags.quantities[4] |
| quantity | 9 of the 12 letters (80% of the total) — capacity of iconic memory extrapolated from the partial-report result — “In extrapolating the partial report’s data to the total, it follows that individuals could report 9 of the 12 letters contained in the instructions (80% of the total), thus demonstrating a large capacity.” | content_tags.quantities[5] |
| quantity | 150–200 ms — latency of motor-region activation after each word during text processing, used to argue activation is not a post-comprehension image — “the activation of motor regions during the processing of a text appears to be rapid, about 150–200 ms after each word” | content_tags.quantities[6] |
| quantity | 9 of the 12 letters — the iconic memory capacity - reached by extrapolating a cued-row result to the whole array, and never observed directly — “Sperling (1960) demonstrated this large capacity after presenting the results of his total and partial reports. The full report consisted in presenting a 3 × 3 or 3 × 4 matrix of alphanumeric characters for a short period of time to subjects and later asking them which characters they remembered. On the other hand, in the partial report, subjects were directed to remember the characters in a row specifically assigned to them in the instructions. The total report’s results showed that subjects were only able to recall between 3 or 4 letters of the total number. However, in the partial report, subjects remembered around 75% of those that were asked. In extrapolating the partial report’s data to the total, it follows that individuals could report 9 of the 12 letters contained in the instructions (80% of the total), thus demonstrating a large capacity.” [ATTRIBUTED TO A CITED AUTHOR, NOT THIS PAPER] the paper’s own words: “Sperling (1960) demonstrated” | content_tags.quantities[7] |
| quantity | three characteristics — the definition of iconic memory - large capacity, short duration and a pre-categorical nature, the last of which was later contradicted — “Subsequent research on visual persistence from Coltheart ( Coltheart, 1983 ) and Sperling’s studies ( Sperling, 1960 ) on the persistence of information led to the definition of three characteristics pertaining to iconic memory: a large capacity, a short duration, and a pre-categorical nature.” | content_tags.quantities[8] |
| variable | capacity — “Subsequent research on visual persistence from Coltheart ( Coltheart, 1983 ) and Sperling’s studies ( Sperling, 1960 ) on the persistence of information led to the definition of three characteristics pertaining to iconic memory: a large capacity, a short duration, and a pre-categorical nature.” | content_tags.variables[0] |
| variable | duration — “Subsequent research on visual persistence from Coltheart ( Coltheart, 1983 ) and Sperling’s studies ( Sperling, 1960 ) on the persistence of information led to the definition of three characteristics pertaining to iconic memory: a large capacity, a short duration, and a pre-categorical nature.” | content_tags.variables[1] |
| variable | attention — “In general, we can say that the central executive controls attention, “the phonological loop ensures retention of verbal information and the visuospatial sketchpad is responsible for storage visual and spatial information” ( Grigorenko et al., 2012 ). The latter two sub-memory systems are equivalent to verbal and visual short-term memory systems, respectively.” | content_tags.variables[2] |
| definition | sensory memory — “Memory “Sensory memory is the capacity for briefly retaining the large amounts of information that people encounter daily” ( Siegler and Alibali, 2005 ).” | content_tags.definitions[0] |
| definition | short-term memory — “Short-term memory is the ability to keep a small amount of information available for a short period of time.” | content_tags.definitions[1] |
| definition | working memory — “Memory “The term working memory refers to a brain system that provides temporary storage and manipulation of the information necessary for such complex cognitive tasks as language comprehension, learning and reasoning” ( Baddeley, 1992 ).” | content_tags.definitions[2] |
| definition | long-term memory — “Long-term memory refers to unlimited storage information to be maintained for long periods, even for life.” | content_tags.definitions[3] |
| definition | iconic memory — “Iconic memory retains information from the sense of sight with an approximate duration of 1 s.” | content_tags.definitions[4] |
| definition | explicit memory — “Explicit memory refers to information that can be consciously evoked.” | content_tags.definitions[5] |
| definition | procedural memory — “Procedural memory is the part of memory that participates in recalling motor and executive skills that are necessary to perform a task.” | content_tags.definitions[6] |
| definition | associative memory — “Associative memory refers to the storage and retrieval of information through association with other information.” | content_tags.definitions[7] |
| definition | non-associative memory — “Non-associative memory is one of three types of non-declarative or implicit memory and refers to newly learned behavior through repeated exposure to an isolated stimulus.” | content_tags.definitions[8] |
| definition | priming — “Priming, the fourth modality of non-declarative or implicit memory, is an effect whereby exposure to certain stimuli influences the response given to stimuli presented later.” | content_tags.definitions[9] |
| definition | central executive — “The central executive is a system of attention control with limited processing capacity.” | content_tags.definitions[11] |
| definition | perceptual memory — “Perceptual memory : memory acquired through the senses. It includes a lot of individual experience; it ranges from the simplest forms of sensory memory to the most abstract knowledge.” | content_tags.definitions[12] |
| definition | long-term potentiation (LTP) — ““LTP is a process whereby brief periods of synaptic activity can produce a long-lasting increase in the strength of a synapse, as shown by an increase in the size of the excitatory postsynaptic current.” | content_tags.definitions[13] |
| definition | sensory memory — ““Sensory memory is the capacity for briefly retaining the large amounts of information that people encounter daily” ( Siegler and Alibali, 2005 ). There are three types of sensory memory: echoic memory, iconic memory, and haptic memory. Iconic memory retains information that is gathered through sight, echoic memory retains information gathered through auditory stimuli and haptic memory retains data acquired through touch.” | content_tags.definitions[14] |
| definition | working memory — ““The term working memory refers to a brain system that provides temporary storage and manipulation of the information necessary for such complex cognitive tasks as language comprehension, learning and reasoning” ( Baddeley, 1992 ). At first (1974), they proposed the existence of three subsystems within the multi-storehouse model of short-term memory: the central executive, a phonological or articulatory loop and a visuospatial sketchpad.” | content_tags.definitions[15] |
| definition | priming — “Priming, the fourth modality of non-declarative or implicit memory, is an effect whereby exposure to certain stimuli influences the response given to stimuli presented later. An example is in order. If you present a list of words to a person that contains the word ‘ball,’ and then the person is asked to participate in a task to complete words, they are more likely to respond with the word ball to the presentation of the word bowl than if they had not previously seen that word in the original list. Thus, the priming capacity can affect the choice of a particular word on a test to complete words, even long after conscious recollection of the primed words has been forgotten.” | content_tags.definitions[16] |
| definition | episodic — “Episodic memory : “involves the ability to learn, store, and retrieve information about unique personal experiences that occur in daily life. These memories typically include information about the time and place of an event, as well as detailed information about the event itself” | content_tags.definitions[17] |
| definition | explicit — “Explicit/declarative memory : refers to conscious memories of previously stored experiences, facts and concepts that are verifiable through a verbal reporting of them” | content_tags.definitions[18] |
| definition | associative — “Associative memory : refers to the storage and retrieval of information resulting from an association (i.e., resulting from an association with other information). Two types of conditioning are involved in its acquisition: classical conditioning and operant conditioning. Classical conditioning is a kind of associative learning between stimuli and behavior, and operant conditioning is a form of learning in which new behaviors develop in terms of their consequences.” | content_tags.definitions[19] |
| definition | LTP — “The research of the cellular and molecular substrates of memory has received much attention since Lomo (1966) described in the 60’s “a cellular model of experience-dependent plasticity—long-term potentiation (LTP)” ( Kandel et al., 2014 ). According to Lisman et al. (2012) : “LTP is a process whereby brief periods of synaptic activity can produce a long-lasting increase in the strength of a synapse, as shown by an increase in the size of the excitatory postsynaptic current.” | content_tags.definitions[20] |
| definition | episodic buffer — “Conceptual short-term memory/episodic buffer : This is a temporary storage system capable of integrating information from different sources that is probably controlled by the central executive. It is episodic in that it has episodes in which information is integrated through space and, potentially, extended through time.” | content_tags.definitions[21] |
| key-terms | memory, classification, model, definition, glossary, terminology, sensory memory, short-term memory, long-term memory, working memory, explicit, implicit, declarative, non-declarative, episodic, semantic, procedural, associative, priming, iconic, echoic, haptic, storehouse, storage, capacity, duration, pre-categorical, Sperling, partial report, central executive, phonological, visuospatial, sketchpad, episodic buffer, subsystem, attention, conscious, unconscious, unitary, HM, skill, amnesic, syndrome, Williams, Down, conditioning, learning, LTP, consolidation, retrieval, amygdala |
| concept | sensory memory — not defined in this paper's own words; the first of the three main forms — “The three major classifications of memory that the scientific community deals with today are as follows: sensory memory, short-term memory, and long-term memory. Information from the world around us begins to be stored by sensory memory, making it possible for this information to be accessible in the future. Short-term memory refers to the information processed by the individual in a short period of time. Working memory performs this processing. Long-term memory allows us to store information for long periods of time. This information may be retrieved consciously (explicit memory) or unconsciously (implicit memory).” | concepts[6] |
| concept | short-term memory — not defined in this paper's own words; the second — “The three major classifications of memory that the scientific community deals with today are as follows: sensory memory, short-term memory, and long-term memory. Information from the world around us begins to be stored by sensory memory, making it possible for this information to be accessible in the future. Short-term memory refers to the information processed by the individual in a short period of time. Working memory performs this processing. Long-term memory allows us to store information for long periods of time. This information may be retrieved consciously (explicit memory) or unconsciously (implicit memory).” | concepts[7] |
| concept | episodic — not defined in this paper's own words; memory for events, with time and place — “Explicit memory consists of episodic memory (time-related events) and semantic memory (concepts and meanings).” | concepts[14] |
| concept | semantic — not defined in this paper's own words; memory for meanings and concepts — “Explicit memory consists of episodic memory (time-related events) and semantic memory (concepts and meanings).” | concepts[15] |
| concept | procedural — not defined in this paper's own words; memory for motor and executive skills — “Procedural memory is the part of memory that participates in recalling motor and executive skills that are necessary to perform a task.” | concepts[16] |
| concept | central executive — not defined in this paper's own words; the attention controller of working memory — “Working memory consists of four elements that process information: the central executive (attention control), the visuospatial sketchpad (creates and maintains a visuospatial representation), the phonological buffer (stores and consolidates new words), and the episodic buffer (stores and integrates information from different sources).” | concepts[29] |
| concept | attention — not defined in this paper's own words; what the central executive controls — “The central executive is a system of attention control with limited processing capacity.” | concepts[35] |
| concept | unconscious — not defined in this paper's own words; its other side — “It is an executive system that guides activity and usually works at an unconscious level.” | concepts[37] |
| concept | skill — not defined in this paper's own words; what he acquired, and what the field then set aside — “A skill is thought to be acquired when behavior changes as a result of experience or practice.” | concepts[40] |
| concept | amnesic — not defined in this paper's own words; the patients in whom priming survives — “These studies show that severely amnesic patients can exhibit completely intact priming while performing memory tests that include conventional recognition” | concepts[41] |
| concept | conditioning — not defined in this paper's own words; how associative memory is acquired — “Two types of conditioning are involved in its acquisition: classical conditioning and operant conditioning.” | concepts[45] |
| concept | consolidation — not defined in this paper's own words; the fixing of a memory — “Furthermore, in human beings, this process of consolidation is thought to contribute to the development of procedural knowledge” | concepts[48] |
| concept | retrieval — not defined in this paper's own words; its recovery, which destabilises it again — “Finally the hippocampus is responsible for the formation and retrieval of memories.” | concepts[49] |
| concept | amygdala — not defined in this paper's own words; the proposed nexus for emotional enhancement — “Evidence suggests that it is the amygdala that is most responsible for the enhancement of memory” | concepts[50] |
| concept | hippocampus — not defined in this paper's own words; ONE OF 24 RECORDS CARRYING THIS TERM AND, UNTIL NOW, THE ONLY QUOTE FOR ANY OF THEM. 'the hippocampus is responsible for the formation and retrieval of memories' - two jobs, and the corpus's most-shared ungrounded term finally has a sentence behind it on one record — “Finally the hippocampus is responsible for the formation and retrieval of memories.” | concepts[51] |
| partial report | — “Sperling (1960) demonstrated this large capacity after presenting the results of his total and partial reports. The full report consisted in presenting a 3 × 3 or 3 × 4 matrix of alphanumeric characters for a short period of time to subjects and later asking them which characters they remembered. On the other hand, in the partial report, subjects were directed to remember the characters in a row specifically assigned to them in the instructions. The total report’s results showed that subjects were only able to recall between 3 or 4 letters of the total number. However, in the partial report, subjects remembered around 75% of those that were asked. In extrapolating the partial report’s data to the total, it follows that individuals could report 9 of the 12 letters contained in the instructions (80% of the total), thus demonstrating a large capacity.” [ATTRIBUTED TO A CITED AUTHOR, NOT THIS PAPER] the paper’s own words: “Sperling (1960) demonstrated” | content_tags.statistics[0] |
| claim type | critique — a second reading DIFFERING from the recorded value; recorded: existence — “This review aims to classify and clarify, from a neuroanatomical, neurophysiological, and psychological perspective, different memory models that are currently widespread in the literature as well as to describe their origins. We believe it is important to consider previous developments without which one cannot adequately understand the kinds of models that are now current in the scientific literature. This article intends to provide a comprehensive and rigorous overview for understanding and ordering the latest scientific advances related to this subject.” | alternatives.claim_type |
| method | historical review, organised by the author and year that introduced each distinction, ending in a glossary offered as partial — a second reading DIFFERING from the recorded value; recorded: review — “Finally, the following glossary includes commentary about the terminology that, in our opinion, is essential for an introductory overview, enabling interested students and professionals to effectively approach the latest memory-related discoveries. This commentary is not intended as an exhaustive definition, but rather collects relevant information to situate the reader within a complex panorama.” | alternatives.method |
| phenomenon | memory as a set of separable systems rather than one faculty, and the terminology that separates them — a second reading DIFFERING from the recorded value; recorded: human memory systems — “The three major classifications of memory that the scientific community deals with today are as follows: sensory memory, short-term memory, and long-term memory. Information from the world around us begins to be stored by sensory memory, making it possible for this information to be accessible in the future. Short-term memory refers to the information processed by the individual in a short period of time. Working memory performs this processing. Long-term memory allows us to store information for long periods of time. This information may be retrieved consciously (explicit memory) or unconsciously (implicit memory).” | alternatives.phenomenon |
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The Neuroanatomical, Neurophysiological and Psychological Basis of Memoryterm·dom: Current Modelsterm and Their Origins Eduardo CaminapersName Eduardo CaminapersName 1 Mind-Brain Group: Biology and Subjectivity in Philosophy and Contemporary Neuroscience, Institute for Culture and Society, University of Navarra, Pamplona, Spain 2 Department of Learningterm·dom and Curriculum, Faculty of Education and Psychology, University of Navarra, Pamplona, Spain 1, 2 , Francisco GüellpersName Francisco GüellpersName 1 Mind-Brain Group: Biology and Subjectivity in Philosophy and Contemporary Neuroscience, Institute for Culture and Society, University of Navarra, Pamplona, Spain 1, * 1 Mind-Brain Group: Biology and Subjectivity in Philosophy and Contemporary Neuroscience, Institute for Culture and Society, University of Navarra, Pamplona, Spain 2 Department of Learningterm·dom and Curriculum, Faculty of Education and Psychology, University of Navarra, Pamplona, Spain Edited by: Antonella Gasbarri, University of L’Aquila, Italy Reviewed by: Alfredo Meneses, Center for Research and Advanced Studies of the National Polytechnic Institute (CINVESTAV), Mexico; Carlos Alberto Blanco, Comillas Pontifical University, Spain; Elif Engin, McLean Hospital, United States; Francis Bambico, Centre for Addiction and Mental Health, Canada ✉ *Correspondence: Francisco GüellpersName, fguell@unav.es This article was submitted to Neuropharmacology, a section of the journal Frontiers in Pharmacology Received 2017 Feb 13; Accepted 2017 Jun 19; Collection date 2017.
Copyright © 2017 CaminapersName and GüellpersName.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
PMCID: PMC5491610 PMID: 28713278 Abstract This reviewterm·mth aims to classify and clarify, from a neuroanatomical, neurophysiological, and psychological perspective, different memoryterm·dom modelsterm that are currently widespread in the literature as well as to describe their origins. We believe it is important to consider previous developments without which one cannot adequately understand the kinds of modelsterm that are now current in the scientific literature. This article intends to provide a comprehensive and rigorous overview for understanding and ordering the latest scientific advances related to this subject. The main forms of memoryterm·dom presented include sensory memoryterm·dom, short-term memoryterm·dom, and long-term memoryterm·dom. Information from the world around us is first stored by sensory memoryterm·dom, thus enabling the storageterm and future use of such information. Short-term memoryterm·dom (or memoryterm·dom) refers to information processed in a short period of time. Long-term memoryterm·dom allows us to store information for long periods of time, including information that can be retrieved consciously (explicit memoryterm·def) or unconsciously (implicitterm memoryterm·dom).
Keywords: explicit memoryterm·def, sensory memoryterm·dom, implicitterm memoryterm·dom, long-term memoryterm·dom, short-term memoryterm·dom Introduction A life full of unconnected events, of errors that do not lead to any lessons and of emotions without the ability to remember them is no life at all. Memoryterm·dom is precisely the capacityterm that allows us to connect experiences, learn and make sense of our lives. In short, it allows us to build our story. The full range of this complex capacityterm’s neuroanatomical, neurobiological, neurophysiological, and psychological mechanism remain unknown and it presents a challenge for psychologists and neuroscientists who try to explain it. This reviewterm·mth attempts to provide a rigorous overview that permits anyone who wants to approach the latest scientific findings on memoryterm·dom to do so, as well as to understand them and properly order them. We will focus on neuroanatomical, neurophysiological, and psychological mechanisms of the different types of memoryterm·dom.
Although knowledge of molecular mechanisms is important for constructing a complete vision of memoryterm·dom modelsterm, in this article we can only point out general traits as summarized in this introduction [for more information see ( Kandel et al., 2014 )]. In addition, knowledge gained from neuroimaging studies ( Binder and Desai, 2011 ), as well as knowledge of the neural markers associated with memoryterm·dom ( Meneses, 2015 ), will likely play a key role in future modelsterm of memoryterm·dom mechanisms, but in this reviewterm·mth, as stated above, we focus mainly on neuroanatomical, neurophysiological, and psychological mechanisms.
We believe it is important to consider previous developments without which one cannot adequately understand the classificationsterm of memories and the kinds of memoryterm·dom modelsterm that are now current in the scientific literature.
The three major classificationsterm of memoryterm·dom that the scientific community deals with today are as follows: sensory memoryterm·dom, short-term memoryterm·dom, and long-term memoryterm·dom. Information from the world around us begins to be stored by sensory memoryterm·dom, making it possible for this information to be accessible in the future. Short-term memoryterm·dom refers to the information processed by the individual in a short period of time. Working memoryterm·dom performs this processing. Long-term memoryterm·dom allows us to store information for long periods of time. This information may be retrieved consciously (explicit memoryterm·def) or unconsciously (implicitterm memoryterm·dom).
As Squire (2004) points out, the first theoretical approaches relevant to current neuroscience come from the 19th century. These include Maine de Biran (1804/1929) ( Maine de Biran, 1929 ) who, at the beginning of the century, wrote of mechanical memoryterm·dom, sensitive memoryterm·dom, and representative memoryterm·dom. The philosopher James, and his book The Principles of Psychology ( James, 1890 ), is also especially worth highlighting. Therein, James distinguishes between primary and secondary memoryterm·dom, thereby referring to short- and long-term memoryterm·dom, respectively.
The importance of Pavlov (1927) and Fitts and Posner (1967) are especially noteworthy during the first two thirds of the 20th century. Pavlov’s studies are related to a type of memoryterm·dom that later would be called associative memoryterm·def. Meanwhile, Fitts and Posner’s studies are considered the first modelterm to explain procedural memoryterm·def.
Prior to the 60’s, most systematizations of memoryterm·dom distinguished a more mechanical type of memoryterm·dom related to the acquisition of skillsterm, which is, in turn, related to activity of the intellect. Unlike what followed, debates in this period were mainly philosophical or based on psychological intuition ( Ribot, 1881 ; Korsafoff, 1890 ).
Beginning in the 1960s, a series of experimental studies on how the brain stores information emerged, using animals and amnesicterm patients. Within this decade, Milner, Atkinson, and Shiffrin were especially important researchers.
The experimental modern era arguably began when Milner (1962) demonstrated, with HMterm experiments, that a seriously ill patient could acquire a new skillterm (hand-eye coordination) without any memoryterm·dom of having encountered the task before. “While this finding showed that memoryterm·dom is not unitaryterm, discussions at the time tended to set aside motor skillsterm as a special case representing a less cognitive form of memoryterm·dom. The suggestion was that the rest of memoryterm·dom is of one piece and is dependent on medial temporal lobe structures” ( Squire and Wixted, 2016 ).
A few years later, Atkinson and Shiffrin (1968) proposed a modal modelterm of memoryterm·dom that constitutes one of the most influential explanations for the existence of different components in the memoryterm·dom system. The importance of this modelterm is such that it must be explained in the next section, but for now it should simply be mentioned that the modal modelterm establishes the existence of short-term storageterm (ACP), which receives sensory information that is processed by sensory and data storehousesterm within long-term memoryterm·dom. This storageterm system can generate reasoning and new deductions from existing ones.
In the seventies, Tulving, Baddeley, and Hitch and Kandel’s investigations are especially noteworthy. Tulving (1972) first proposed the distinction between episodicterm·dom memoryterm·dom and semanticterm·dom memoryterm·dom. Baddeley and Hitch (1974) conducted research on the components of working memoryterm·dom. Both authors considered working memoryterm·dom as a limited capacityterm system that allows temporary storageterm and manipulation of information necessary to perform complex tasks such as understanding, learningterm·dom, and reasoning. As explained later on, at first (1974), they proposed the existence of three subsystemsterm within the multi-storehouse modelterm of short-term memoryterm·dom: the central executiveterm, a phonologicalterm or articulatory loop and a visuospatialterm sketchpadterm. Later, Baddeley (2000) included a fourth subsystemterm, the episodic bufferterm, which combines information from the subsystemsterm in a form of temporal representation. Kandel (1976) proposed a modelterm to explain the mechanism of operation in habituation and sensitization. To do this, he used the notion of non-associative memoryterm·def, which, as we shall see, is one of the four types of non-declarativeterm or implicitterm memoryterm·dom, like that which refers to new behaviors learned through repeated exposure to a single stimulus. According to Kandel, new behaviors can be classified into two processes: sensitization and habituation. On the one hand, for habituation, acetylcholine is progressively consumed, decreasing the effectiveness of the stimulus and thereby the motor response. On the other hand, the presence of serotonin in sensitization, secreted by another sensory nerve terminal, causes an excess of acetylcholine. An enhanced motor response thus emerges.
In the 1980s, the differences between declarativeterm and non-declarativeterm memories were consolidated and disseminated. This, together with contributions from Tulving and others, such as Di Lollo or Graf and Schacter, enabled a more precise classificationterm of different types of memoryterm·dom. To date, Di Lollo’s modelterm of iconic memoryterm·def ( Di Lollo, 1980 ) has been the most widely accepted and studied of the three existing types of sensory memoryterm·dom. As discussed in the next section, Di Lollo considered iconic memoryterm·def a storageterm unit consisting of two components: the persistence of vision and information. Graf and Schacter (1985) proposed a general difference between declarativeterm memoryterm·dom (explicitterm) and non-declarativeterm memoryterm·dom (implicitterm/proceduralterm·dom). This stems from the distinction that Tulving (1972) proposed between the aforementioned episodicterm·dom memoryterm·dom and semanticterm·dom memoryterm·dom (both, as we will see, are currently included in declarativeterm memoryterm·dom).
In the 90’s, a classificationterm of the types of memoryterm·dom emerged, but the way they act and their interrelation was still unclear. In order to clarify its operation, Packard and McGaugh (1996) proposed that memoryterm·dom systems operate independently and in parallel. For example, an adverse event in childhood (e.g., seeing your grandfather being run over by a combine) can, on the one hand, consolidate as a stable declarativeterm memoryterm·dom for the event itself (the sound of a combine always makes you remember that moment-episodic memoryterm·dom) and, on the other hand, can crystallize in non-declarativeterm memoryterm·dom and result in a phobia experienced as a personality trait rather than as a mere memoryterm·dom (being near a combine will always produce panic and induces a desire to escape that situation-associative memoryterm·dom). Several authors ( Tulving et al., 1982 ) had already mentioned the idea of primingterm·dom as a separate type of memoryterm·dom, but it was not until the 90’s that experiments were conducted to show it ( Hamann and Squire, 1997 ; Stark and Squire, 2000 ; Levy et al., 2004 ). These studies show that severely amnesicterm patients can exhibit completely intact primingterm·dom while performing memoryterm·dom tests that include conventional recognition of the same test items ( Squire, 2004 ).
Thanks to the development of new 21st century technologies, researchers have been able to more accurately locate brain areas that are associated with different types of memoryterm·dom. Although this pertains to topics to be addressed in detail in the next section, there are two examples that we consider significant to the application of these new techniques and the significant progress made in understanding memoryterm·dom storageterm. On the one hand, Ergorul and Eichenbaum’s experiment ( Ergorul and Eichenbaum, 2004 ) shows that animals are able to remember the “context in which they experienced specific stimuli, and that this capacityterm also depends on the hippocampusterm·dom” ( Dickerson and Eichenbaum, 2010 ). This process is closely related to the formation of episodicterm·dom memoryterm·dom. On the other hand, neuroimaging studies that Binder and Desai (2011) conducted show “two striking results: the participation of modality-specific sensory, motor, and emotion systems in language comprehension, and the existence of large brain regions that participate in comprehension tasks but are not modality-specific.” With this in mind, Binder and Desai (2011) claims that semanticterm·dom memoryterm·dom consists of two representations, including a specific mode and a supramodal mode. Again, this will be explained in more detail in what follows.
The research of the cellular and molecular substrates of memoryterm·dom has received much attentionterm since Lomo (1966) described in the 60’s “a cellular modelterm of experience-dependent plasticity—long-term potentiation (LTP)term·def” ( Kandel et al., 2014 ). According to Lisman et al. (2012) : “LTPterm is a process whereby brief periods of synaptic activity can produce a long-lasting increase in the strength of a synapse, as shown by an increase in the size of the excitatory postsynaptic current.” NMDA receptors are double-gated, as their activation requires both postsynaptic membrane depolarization as well as presynaptic release of glutamate. Once activated by these conditions, NMDA receptors trigger a strong postsynaptic influx of Ca2+ that induce LTPterm through a variety of pathways including CaMKII, PKC, PKA, and MAPK ( Kandel et al., 2014 ).
With this brief historical and conceptual introduction laid out, we intend to delve into different types of memoryterm·dom in order to present the modelsterm that the scientific community has most accepted thus far. In the last section, and before the glossaryterm, we identify the likely directions for future research. Now we turn on to our main task, presenting an overview of the latest scientific findings on memoryterm·dom, classified according to different types and mechanisms.
Sensory Memoryterm·dom: Iconic Memoryterm·def “Sensory memoryterm·dom is the capacityterm for briefly retaining the large amounts of information that people encounter daily” ( Siegler and Alibali, 2005 ). There are three types of sensory memoryterm·dom: echoicterm·dom memoryterm·dom, iconic memoryterm·def, and hapticterm·dom memoryterm·dom. Iconic memoryterm·def retains information that is gathered through sight, echoicterm·dom memoryterm·dom retains information gathered through auditory stimuli and hapticterm·dom memoryterm·dom retains data acquired through touch.
Scientific research has focused mainly on iconic memoryterm·def; information on echoicterm·dom and hapticterm·dom memoryterm·dom is comparatively scarce. Thus, taking into account the goals of this article and that it is aimed at a higher education audience, presenting iconic memoryterm·def as a paradigm of sensory memoryterm·dom is sufficient for an introductory overview.
Iconic memoryterm·def retains information from the sense of sight with an approximate durationterm of 1 s. This reservoir of information then passes to short-term vision memoryterm·dom (which is analogous, as we shall see shortly, to the visuospatialterm sketchpadterm with which working memoryterm·dom operates).
Di Lollo’s modelterm ( Di Lollo, 1980 ) is the most widely accepted modelterm of iconic memoryterm·def. Therein, he considered iconic memoryterm·def a storehouseterm constituted by two components: the persistence of vision and information.
(a) Persistence of vision. Iconic memoryterm·def corresponds to the pre-categoricalterm representation image/visual that remains between 100 and 300 ms. It is sensitive to physical parameters, such that it depends on retinal photoreceptors (rods and cones). It also depends on various cells in the visual system and on retinal ganglion cells M (transition cells) and P (sustained cells). It concludes its representation in the primary visual cortex (V1) of the occipital lobes. “The occipital lobe is responsible for processing visual information” ( Kamel and Malik, 2014 ).
(b) Persistence of information. Iconic memoryterm·def is a storehouseterm of information that lasts 800 ms and that represents a codified and already categorized version of the visual image. It plays the role of storehouseterm for post-categorical memoryterm·dom, which provides visual short-term memoryterm·dom with information to be consolidated. For this, it travels through the ventral route (V) (V1 → V2 → V5 → inferior temporal cortex).
Subsequent research on visual persistence from Coltheart ( Coltheart, 1983 ) and Sperlingterm’s studies ( Sperlingterm, 1960 ) on the persistence of information led to the definitionterm of three characteristics pertaining to iconic memoryterm·def: a large capacityterm, a short durationterm, and a pre-categoricalterm nature.
Sperlingterm (1960) demonstrated this large capacityterm after presenting the results of his total and partial reportsterm·mth. The full report consisted in presenting a 3 × 3 or 3 × 4 matrix of alphanumeric characters for a short period of time to subjects and later asking them which characters they remembered. On the other hand, in the partial reportterm·mth, subjects were directed to remember the characters in a row specifically assigned to them in the instructions. The total report’s results showed that subjects were only able to recall between 3 or 4 letters of the total number. However, in the partial reportterm·mth, subjects remembered around 75% of those that were asked. In extrapolating the partial reportterm·mth’s data to the total, it follows that individuals could report 9 of the 12 letters contained in the instructions (80% of the total), thus demonstrating a large capacityterm.
Regarding short-term, Sperlingterm interpreted the results of the partial reportterm·mth as due to the rapid decline of the visual sign and reaffirmed this short durationterm by obtaining a decrease in the number of letters reported by the subject in delaying the audio signal for choosing a row to remember in the presentation. Averbach and Coriell’s experiments ( Averbach and Coriell, 1961 ) corroborated Sperlingterm’s conclusion; they presented a variety of letters for a certain period of time to the subject. After each letter, and in the same position, they showed a particular visual sign. The participant’s task was to name the letter that occupied the position of the visual sign. When the visual sign appeared immediately after the letters, participants could correctly name the letter that occupied the position of the sign, however, as the presentation of the sign became more delayed, participant performance worsened. These results also show the rapid decline of visual information.
Finally, regarding its pre-categoricalterm nature, Sperlingterm considered the information contained in this storehouseterm as physical information that maintains the raw data that is not related to the meaning of stimuli. Subsequently, evidence has been obtained that this system is not entirely pre-categoricalterm ( Loftus et al., 1992 ) since the task improves when the stimuli to remember are letters or numbers instead of meaningless forms.
Short-Term Memoryterm·dom Short-term memoryterm·dom is the ability to keep a small amount of information available for a short period of time. Atkinson and Shiffrin’s modal modelterm ( Atkinson and Shiffrin, 1968 ) is one of the most influential explanations for the existence of different components in the memoryterm·dom system ( Figure 1 ). This modelterm has some similarities with Broadbent’s previous modelterm ( Broadbent, 1958 ). The modal modelterm establishes the existence of a short-term storehouseterm with limited capacityterm. The short-term storehouseterm receives sensory information processed by sensory storehousesterm and data in long-term memoryterm·dom. In addition, the short-term storehouseterm can also send information to the structures involved in long-term memoryterm·dom. This storehouseterm can generate reasoning and new deductions from existing ones. This modelterm implies that the short-term storehouseterm functions as a kind of working memoryterm·dom, a system to retain and manipulate information temporarily as part of a wide range of essential cognitive tasks such as learningterm·dom, reasoning, and understanding. They, in turn, give short-term storageterm central importance in the overall processing of information by attributing to it the role of controlling the executive system, responsible for the coordination and control of many complex subroutines in charge of acquiring new material and recovering old material in long-term storageterm.
FIGURE 1.
Atkinson and Shiffrin’s modal modelterm.
Despite the explanatory power of Atkinson and Shiffrin’s modelterm, there were a number of issues that this modelterm could not resolve, causing criticism of it. For example, this modelterm implies that the longer an item remains in memoryterm·dom, the more likely it is to be transferred to long-term storageterm. But studies like those of Tulving and Pearlstone (1966) and Craik and Watkins (1973) show that said relationship does not exist.
Given these criticisms, new modelsterm began to appear to explain memoryterm·dom, such as those from Cowan (1988 , 1995 , 1999 ) and Goldman-Rakic (1995) . Among them, Craik and Lockhart’s process modelterm ( Craik and Lockhart, 1972 ) and Baddeley and Hitch’s structural modelterm ( Baddeley and Hitch, 1974 ) were the most prominent; the latter is the most commonly accepted one today and thus we will focus on it in this article.
As an introduction, it can be argued that Craik and Lockhart (1972) understood memoryterm·dom not as a process through which information is deepened at higher levels until it becomes part of long-term memoryterm·dom, but rather as a system of storehousesterm. Despite an emphasis on information processing (instead of structure), they continued to accept the existence of short-term memoryterm·dom as independent from long-term memoryterm·dom. For their part, Baddeley and Hitch’s proposal ( Baddeley and Hitch, 1974 ) contemplated a multi-component working memoryterm·dom instead of a storageterm unit in the short term.
Working Memoryterm·dom “The term working memoryterm·dom refers to a brain system that provides temporary storageterm and manipulation of the information necessary for such complex cognitive tasks as language comprehension, learningterm·dom and reasoning” ( Baddeley, 1992 ). At first (1974), they proposed the existence of three subsystemsterm within the multi-storehouse modelterm of short-term memoryterm·dom: the central executiveterm, a phonologicalterm or articulatory loop and a visuospatialterm sketchpadterm.
In general, we can say that the central executiveterm controls attentionterm, “the phonologicalterm loop ensures retention of verbal information and the visuospatialterm sketchpadterm is responsible for storageterm visual and spatial information” ( Grigorenko et al., 2012 ). The latter two sub-memory systems are equivalent to verbal and visual short-term memoryterm·dom systems, respectively.
Wang and Bellugi (1994) presented a genetically based test that supports the functional and anatomical separation of Baddeley’s modelterm with phonologicalterm and visuospatialterm storehousesterm. They compared two genetic syndromesterm (Williamsterm and Downterm) with different brain morphology. Williamsterm syndrometerm patients, despite having widespread mental handicaps, preserve their language skillsterm, while Downterm syndrometerm patients preserve more partial capacities, but have very limited language skillsterm. It was therefore assumed that the former would be better at verbal tasks related to operative memoryterm·dom, and that the latter would be better at visuospatialterm tasks related to operative memoryterm·dom. As expected, subjects with Williamsterm syndrometerm performed better at phonologicalterm tasks, while subjects with Downterm syndrometerm, in turn, performed better at spatial tasks.
Later, Baddeley (2000) included a fourth subsystemterm, the episodic bufferterm ( Figure 2 ), which combines information from the different subsystemsterm in a kind of temporal representation.
FIGURE 2.
Baddeley’s modelterm.
Here we will focus on the different subsystemsterm that make up Baddeley’s multi-storehouse modelterm (2000), i.e., the central executiveterm, the phonologicalterm or articulatory loop, the visuospatialterm sketchpadterm and the episodic bufferterm.
The Central Executiveterm The central executiveterm is a system of attentionterm control with limited processing capacityterm. Baddeley (1986) adopted a modelterm originally proposed by Norman and Shallice (1986) , in which actions are controlled in two ways. “Behavior that is routine and habitual is controlled automatically by a range of schemas, well-learned processes that allow us to respond appropriately to the environment” ( Baddeley and Hitch, 2010 ). Processes that are not recognized as habitual are controlled by a second system, the supervisory attentionterm system. This system uses long-term knowledge to propose novel behavioral solutions and to weigh options before deciding on a response.
In its original version, the central executiveterm was considered an overall system capable of processing and storing. However, Baddeley and Logie (1999) proposed that it only has attentionterm capacityterm.
Subsequent studies have proposed to complement the executive system with the episodic bufferterm as other separate storageterm system: “the episodic bufferterm clearly does represent a change within the working memoryterm·dom framework, whether conceived as a new component, or as a fractionation of the older version of the central executiveterm”( Baddeley, 2000 ).
Baddeley and Logie understand the central executiveterm as the result of the integration of several processes: the ability to focus attentionterm, the ability to divide attentionterm between two or more tasks, and the ability to control long-term memoryterm·dom access ( Baddeley et al., 1991 ; Logie et al., 2004 ; Baddeley, 2007 ). The way to accomplish this may be with one or more types of inhibition ( Engle et al., 1999 ; Miyake et al., 2000 ). This approach accepts that the frontal lobes play an important role in executive control, although there are differing opinions on the functions’ precise location ( Duncan and Owen, 2000 ; Shallice, 2002 ).
Visuospatialterm Sketchpadterm It has been suggested that the sketchpadterm’s main function is to create and maintain a visuospatialterm representation that persists through the irregular form found in eye movement and that characterizes our exploration of the visual world ( Luck, 2007 ).
It has been shown that spatial tasks such as driving a car can interfere with spatial skillsterm, while exclusively visual tasks, such as watching a series of images or colored shapes, can interfere with the recall of objects or shapes ( Logie, 1986 ; Klauer and Zhao, 2004 ). These patterns of interference, together with cases of brain-damaged patients that show a deficit in one kind of task but not the other ( Della Sala and Logie, 2002 ), suggest that spatial information and visual characteristics can be stored separately.
The visuospatialterm sketchpadterm seems to involve a number of areas, predominantly in the brain’s right hemisphere. On the one hand, it contains a visual component that reflects the processing and storageterm of objects and their visual features. On the other hand, it contains a second parietal area, presumably involved in spatial aspects.
Phonologicalterm Buffer It can be argued that the phonologicalterm buffer supports language acquisition by providing the ability to store new words, while they are consolidated into long-term memoryterm·dom ( Baddeley et al., 1998 ). Within this phonologicalterm loop, two basic sub-processes emerge: a short-term acoustic storehouseterm and a subvocal articulatory rehearsal process. The existence of the former is indicated by the effect of phonologicalterm similarity, where speech is less accurate when repeating “similar-sounding words such as MAN CAP CAT MAT CAN, than dissimilar words such as PIT DAY COW PEN TOP. Similarity of meaning (HUGE LARGE BIG WIDE TALL) has little effect on immediate recall. On the other hand if several trials are given to learn a longer list of say 10 words, meaning becomes all-important and sound loses it power, consistent with different systems for short-term and long-term storageterm ( Baddeley, 1966a , b ). Evidence for the importance of rehearsal comes from the word length effect, whereby immediate recall of long words (e.g., REFRIGERATOR UNIVERSITY TUBERCULOSIS OPPORTUNITY HIPPOPOTAMUS) is much more error-prone than for short words ( Baddeley et al., 1975 )” ( Baddeley and Hitch, 2010 ). Baddeley and Hitch (1974) proposed that retention of items in the short-term storehouseterm quickly fade, but can be maintained by repeating them.
With respect to cerebral location, the phonologicalterm loop is found in the brain’s left hemisphere “The loop is assumed to hold verbal and acoustic information using a temporary store and an articulatory rehearsal system, which clinical lesion studies, and subsequently neuroradiological studies, suggested are principally associated with Brodmann areas, 40 and 44, respectively” ( Baddeley, 2000 ).
Episodic Bufferterm The verbal and visual systems within the conventional modelterm of working memoryterm·dom may explain many aspects, but Baddeley (2000) points out that evidence from patients with short-term memoryterm·dom deficits— who resist memorizing prose (with a verbal span much higher than that of isolated words) and resist serial memoryterm·dom of articulatory suppression— leads to supposing that a storehouseterm of additional support exists. This is seen in the existence of a new mechanism that combines information from multiple subsystemsterm into a form of temporal representation. Baddeley (2000) proposed the term episodic bufferterm for this new kind of representation.
The episodic bufferterm is thus a temporary storageterm system capable of integrating information from different sources, likely controlled by the central executiveterm. “The buffer is episodicterm·dom in the sense that it holds episodes whereby information is integrated across space and potentially extended across time” ( Baddeley, 2000 ). It can be preserved in patients with advanced amnesia and severe impairment of long-term episodicterm·dom memoryterm·dom.
With that said, it is possible to consider the episodic bufferterm as conceptual short-term memoryterm·dom. Studies to date do not specify activity in a specific area. As Potter (1999) said: “The conceptual short-term memoryterm·dom hypothesis proposes that when a stimulus is identified, its meaning is rapidly activated and maintained briefly in conceptual short-term memoryterm·dom.”
Long-Term Memoryterm·dom Long-term memoryterm·dom refers to unlimited storageterm information to be maintained for long periods, even for life. There are two types of long-term memoryterm·dom: declarativeterm or explicit memoryterm·def and non-declarativeterm or implicitterm memoryterm·dom.
Explicit memoryterm·def refers to information that can be consciously evoked. There are two types of declarativeterm memoryterm·dom: episodicterm·dom memoryterm·dom and semanticterm·dom memoryterm·dom. For its part, implicitterm memoryterm·dom encompasses all unconsciousterm memories, such as certain abilities or skillsterm. There are four types of implicitterm memoryterm·dom, including proceduralterm·dom, associativeterm·dom, non-associative, and primingterm·dom.
Declarativeterm/Explicit Memoryterm·def Explicit memoryterm·def refers to information that can be evoked consciously. There are two types of declarativeterm memoryterm·dom: episodicterm·dom memoryterm·dom and semanticterm·dom memoryterm·dom. As shown below, episodicterm·dom memoryterm·dom stores personal experiences and semanticterm·dom memoryterm·dom stores information about facts.
Episodicterm·dom Memoryterm·dom “Episodicterm·dom memoryterm·dom involves the ability to learn, store, and retrieve information about unique personal experiences that occur in daily life. These memories typically include information about the time and place of an event, as well as detailed information about the event itself.” ( Dickerson and Eichenbaum, 2010 ).
There are a number of neural components that are closely related to the proper functioning of episodicterm·dom memoryterm·dom, which include the following: the cortex near the hippocampusterm·dom [as discussed below, the perirhinal cortex (PRC), the entorhinal cortex, and the parahippocampal cortex (PHC)], cortical and subcortical structures, and the circuits within the medial temporal lobe and hippocampusterm·dom.
The cortices near the hippocampusterm·dom extensively interact with a number of cortical and subcortical structures; cortical components have key roles in various aspects of perception and cognition, while the medial temporal lobe structures mediate the organization and the persistence of the memoryterm·dom network, whose data is stored in these cortical areas ( Dickerson and Eichenbaum, 2010 ).
The structures directly related to the hippocampusterm·dom include the entorhinal, the parahippocampal, and the perirhinal cortices. Each one is discussed in detail below.
The entorhinal cortex is the main interface between the hippocampusterm·dom and neocortex, thus it is associated with the distribution of information to and from the hippocampusterm·dom. The surface layers (II and III) of the entorhinal cortex project out toward the dentate gyrus and hippocampusterm·dom. While layer II mainly projects out toward the dentate gyrus and the CA3 region of the hippocampusterm·dom, layer III mainly projects out toward the hippocampal CA1 region and the subiculum. These layers receive input signals from other cortical areas, particularly the association cortices, the PRC and the parahippocampal gyrus, as well as the prefrontal cortex. Layers II and III receive highly processed inputs from each sensory modality, and inputs related to ongoing cognitive processes. Deep layers, particularly layer V, receive one of the three output signals from the hippocampusterm·dom and, in turn, exchange connections with other cortical areas that project out toward the superficial entorhinal cortex.
The PRC has a role in visual object recognition, while the PHC is involved in the perception of the local environment and processing information related to that place. Thus, fMRI studies indicate that the PHC becomes very active when human subjects receive topographical stimuli such as landscapes or rooms. Epstein and Kanwisher (1998) first described the PHC and Aguirre et al. (1996 , 1998 ) and Ishai et al. (1999) later backed up that description.
Finally the hippocampusterm·dom is responsible for the formation and retrievalterm of memories. That is, the information that the three cortices described above process reach the hippocampusterm·dom where new memories are generated and from which they can later be retrieved. Episodicterm·dom memoryterm·dom recall involves a spatial and temporal context of specific experiences. For further reviewterm·mth of the mechanisms of memoryterm·dom formation see Craver (2003) .
As Dickerson and Eichenbaum (2010) point out in their reviewterm·mth, “several investigators have argued that animals are indeed capable of remembering the context in which they experienced specific stimuli, and that this capacityterm also depends on the hippocampusterm·dom.” Ergorul and Eichenbaum (2004) published a significant study to this effect in which they developed a series of tasks for rats to assess their memoryterm·dom of events, which combined an odor (what), the place of the experience (where), and the relation to other experiences (when). The rats were presented with a sample of an odor in one specific place along the edge of a large open field. Subsequently, as a way of testing their memoryterm·dom, they were presented with a choice between two arbitrarily selected odors in their original locations. The results of the test showed that normal rats use a combination of where and what information to judge the timing of the events, while rats with a damaged hippocampusterm·dom cannot manage to effectively combine what, when, and where information in order to form a recovered memoryterm·dom.
Three years later Eichenbaum et al. (2007) proposed a functional organization of memoryterm·dom’s medial temporal lobe system: “Neocortical input regarding the object features (“what”) converges in the PRC and lateral entorhinal area (LEA), whereas details about the location (“where”) of objects converge in the PHC and medial entorhinal area (MEA). These streams converge in the hippocampusterm·dom, which represents items in the context in which they were experienced. Reverse projections follow the same pathways back to the parahippocampal and neocortical regions”( Eichenbaum et al., 2007 ).
It should be noted that memoryterm·dom of faces is typically associated with activity in the perirhinal and hippocampusterm·dom rostral regions, while memoryterm·dom of objects is typically associated with wider-ranging activity ( Preston et al., 2010 ).
Both results concerning functional an anatomic and characterizations in animal modelsterm are consistent with the hypothesis that is guided by anatomic criteria about the functional organization of the hippocampal system ( Dickerson and Eichenbaum, 2010 ).
“The ventral temporal cortex, including fusiform gyrus, is commonly engaged when pictures of visual objects are presented, and the lateral temporal cortex including superior temporal gyrus is typically engaged during the encoding of auditory information” ( Dickerson and Eichenbaum, 2010 ).
Semanticterm·dom Memoryterm·dom As noted, in the context of long-term memoryterm·dom, there were two types of memoryterm·dom, corresponding to declarativeterm and non-declarativeterm memoryterm·dom. Within declarativeterm memoryterm·dom, we find both episodicterm·dom memoryterm·dom, as discussed above, and semanticterm·dom memoryterm·dom, as discussed below.
Human beings have the ability to represent concepts in language. This ability allows us not only to disseminate conceptual knowledge to others, but also to manipulate, associate, and combine these concepts. Therefore, as Binder and Desai shows, “humans use conceptual knowledge for much more than merely interacting with objects. All of human culture, including science, literature, social institutions, religion, and art, is constructed from conceptual knowledge” ( Binder and Desai, 2011 ). Activities such as reasoning, planning for the future or reminiscing about the past depend on the activation of concepts stored in semanticterm·dom memoryterm·dom ( Mahon and Caramazza, 2008 ).
Binder and Desai showed two striking results related to neuroimaging research: on the one hand, the participation of the specific sensory, motor and emotional modality in understanding language and, on the other hand, the existence of large regions of the brain (the inferior parietal lobe and a large part of the temporal lobe) involved in tasks related to understanding. These latter regions converge on the many currents involved in perception processing, and these convergences allow supramodal representations of perceptual experience that support a variety of conceptual functions, including language, social cognition, object recognition, and the extraordinary human ability to remember the past and imagine the future ( Binder and Desai, 2011 ). Therefore, accepting their argument, semanticterm·dom memoryterm·dom consists of two representations: a specific modality and supramodal modality.
In this regard, Binder and Desai found several objections. A not inconsiderable one is that activations observed in imaging experiments could be an epiphenomenon rather than causally related to understanding. Therefore, the involvement of the motor system for processing a text would contribute to understanding and is not a mere product. Another critical point is the possibility of interpreting that collected activations represent images after understanding takes place. However, and as they showed in their reviewterm·mth ( Binder and Desai, 2011 ), in studies of neuroimaging with high temporal resolution, the activation of motor regions during the processing of a text appears to be rapid, about 150–200 ms after each word ( Pulvermüller et al., 2005 ; Boulenger et al., 2006 ; Hoenig et al., 2008 ; Revill et al., 2008 ).
“These converging results provide compelling evidence that sensory-motor cortices play an essential role in conceptual representation. Although it is often overlooked in reviewsterm·mth of embodied cognition, emotion is as much a modality of experience as sensory and motor processing ( Vigliocco et al., 2009 ). Words and concepts vary in the magnitude and specific type of emotional response they evoke, and these emotional responses are a large part of the meaning of many concepts” ( Binder and Desai, 2011 ).
Following Binder and Desai, brain appears to use supramodal abstract representations for conceptual tasks. In this regard, it can be convincingly argued that the human brain has large areas of cortex that are between the sensory systems and motor modalities and, therefore, Damasio’s idea convergence zones seems plausible ( Damasio, 1989 ). “These heteromodal areas include the inferior parietal cortex (angular and supramarginal gyri), large parts of the middle and inferior temporal gyri, and anterior portions of the fusiform gyrus ( Mesulam, 1985 )” ( Binder and Desai, 2011 ).
A second argument supporting the hypothesis that the brain appears to use supramodal abstract representations during conceptual work comes from patients with damage to the lower and lateral temporal lobe. The clinical profile of semanticterm·dom dementia is marked by progressive atrophy in the temporal lobe and loss of multimodal semanticterm·dom memoryterm·dom ( Hodges et al., 1992 ; Mummery et al., 2000 ). Patients with semanticterm·dom dementia is characterized by a loss of conceptual knowledge, and this loss may reflect the disruption of a central semanticterm·dom hub or the degeneration of a temporosylvian language network for verbal concepts ( Irish et al., 2014 ). These patients manifesting in striking alterations in naming and comprehension ( Irish et al., 2016 ). These patients are “characterized by a clear dissociation between marked single-word comprehension” ( Agosta et al., 2010 ), unable to retrieve the names of objects, irregular word reading deficits, identify the color the correct objects, and sparing of fluency, phonology, syntax and working memoryterm·dom ( Binder and Desai, 2011 ).
Basically, these deficits do not seem to be categorical, constituting further evidence that semanticterm·dom impairment does not imply strongly modal representations and, therefore, the modular and supramodal systems are presented as an interactive continuum of hierarchically ordered neuronal combinations, supporting representations that are progressively more idealized and combined ( Binder and Desai, 2011 ). These systems correspond to Damasio’s idea of areas of local convergence and with Barsalou’s idea of systems of unimodal perceptual symbols ( Lambon Ralph et al., 2007 ). In addition to bottom-up input within their associated modality, each system receives top-down input from other modal and attentionterm systems. These systems are modal in the sense that their output is a analogic or isomorphic representation of the information that they receive bottom-up within their associated modality ( Barsalou, 1999a ).
As observed by Binder and Desai: “These modal convergence zones then converge with each other in higher-level cortices located in the inferior parietal lobe and much of the ventral and lateral temporal lobe (…). One function of these high-level convergences is to bind representations from two or more modalities, such as the sound and visual appearance of an animal, or the visual representation and action knowledge associated with a hand tool ( Wernicke, 1974 ; Damasio, 1989 ; Barsalou, 1999b ; Patterson et al., 2007 ). Such supramodal representations capture similarity structures that define categories, such as the collection of attributes that place ‘pear’ and ‘light bulb’ in different categories despite a superficial similarity of appearance, and ‘pear’ and ‘pine-apple’ in the same category despite very different appearances ( Rogers and McClelland, 2004 ). More generally, supramodal representations allow the efficient manipulation of abstract, schematic conceptual knowledge that characterizes natural language, social cognition, and other forms of highly creative thinking ( Dove, 2011 ; Diefenbach et al., 2013 )” ( Binder and Desai, 2011 ).
Non-declarativeterm/Implied Memoryterm·dom As noted, long-term memoryterm·dom refers to unlimited information storageterm that can be maintained for long periods, even for life. There are two types of long-term memoryterm·dom: declarativeterm or explicit memoryterm·def and non-declarativeterm or implied memoryterm·dom.
Implicitterm memoryterm·dom encompasses all unconsciousterm memories, as well as certain abilities or skillsterm. There are four types of implicitterm memoryterm·dom: proceduralterm·dom, associativeterm·dom, non-associative, and primingterm·dom. Each one is detailed below.
Procedural Memoryterm·def: Habits and Skillterm Procedural memoryterm·def is the part of memoryterm·dom that participates in recalling motor and executive skillsterm that are necessary to perform a task. It is an executive system that guides activity and usually works at an unconsciousterm level. When necessary, proceduralterm·dom memories are retrieved automatically for use in the implementation of complex procedures related to motor and intellectual skillsterm.
Development of these rote capacities occurs through proceduralterm·dom learningterm·dom, that is, by systematically repeating a complex activity until acquiring and automatizing the capacityterm of all neural systems involved in performing the task to work together.
The acquisition of skillsterm requires practice. However, the simple repetition of a task does not ensure skillterm acquisition. A skillterm is thought to be acquired when behavior changes as a result of experience or practice. This is known as learningterm·dom and it is not a directly observable phenomenon. Here we will discuss two modelsterm for acquiring skillsterm.
The first modelterm comes from Fitts’s team ( Fitts, 1954 ; Fitts and Posner, 1967 ). These scientists propose an explanatory modelterm of skillterm acquisition, based on the idea of learningterm·dom as a process in three phases: simple (a) Cognitive phase: The process begins with the acquisition of knowledge about the factors that make up a particular observed behavior. At this point, the psychological process of attentionterm is important. The skillterm to be acquired must be broken downterm into its basic components and one must understand how these components are combined to form a whole in the correct execution of the task ( Fitts, 1954 ; Fitts and Posner, 1967 ).
simple (b) Associativeterm·dom phase: Individual repeated practice takes place until there is an automatic response pattern. As one progresses through this point, the actions that are important for the implementation of a skillterm are learned and become automated, just as any superfluous or ineffective actions disappears. The individual sensory system acquires the exact symbolic and spatial data required for the appropriate execution of the skillterm ( Fitts, 1954 ; Fitts and Posner, 1967 ).
simple (c) Autonomous/proceduralterm·dom phase: This is the final phase and it consists in perfecting acquired skillsterm. The ability to judge which stimuli are important and unimportant improves and a lower level of consciousterm thought is required because the skillterm becomes automated ( Fitts, 1954 ; Fitts and Posner, 1967 ).
The other modelterm corresponds to ( Tadlock, 2005 ) and is called Predictive Cycle. This modelterm proposes that learningterm·dom only requires consciousterm maintenance of the desired end result. The modelterm consists of the following phases: Trial, error, implicitterm result analysis, and decision-making at the implicitterm level of the way in which execution of the next test must be changed for successful implementation. These steps are repeated again and again until the subject builds or remodels his/her neural network so that it can guide the activity without the need for consciousterm thought.
A number of factors are involved when acquiring and implementing skillsterm, including attentionterm and pressure. For the acquisition of a new skillterm one must pay attentionterm to the steps to be undertaken. This process involves using working memoryterm·dom to allow for connecting the different steps involved. Procedural memoryterm·def acquires the habit with the help of the attentionterm span, but it implies a lesser performance. However, with practice, proceduralterm·dom knowledge is developed. Proceduralterm·dom knowledge operates away from working memoryterm·dom, which allows for the implementation of the most automated skillsterm ( Anderson, 1993 ). Meanwhile, pressure can affect the performance of a task in two ways: choking or clutchness. The choking phenomenon occurs when experienced and skilled performers fail under stress. Auto-focus theories suggest that pressure causes an increase in anxiety and self-consciousness concerning correct execution. This ends up causing increased attentionterm directed toward processes directly involved in the execution of the skillterm ( Beilock and Carr, 2001 ). On the other hand, the attentionterm span allows the habit to be acquired in refers to giving a top performance on a given task when pressure is highest.
Because they are especially relevant, we will briefly outline brain components involved in the acquisition of new skillsterm and habits, including the basal ganglia, cerebellum and limbic system.
As Christos and Emmanuel explain ( Constantinidis and Procyk, 2004 ), “basal ganglia are formed by several sub-structures: the striatum, the globus pallidus, the substantia nigra, and the subthalamic nucleus.” The basal ganglia are a collection of nuclei found on both sides of the thalamus, outside of and around the limbic system, but below the cingulate gyrus and within the temporal lobes. The striatum or striate nucleus is the main gateway for information to the basal ganglia. In turn, the striatum receives information from the cerebral cortex. Essentially, there are two parallel processing paths that depart from the striatum, each of which acts in opposition to each other in the control of movement and enables associations with other relevant functional structures ( Beilock and Carr, 2001 ). Both work together as a neuronal feedback loop. There are many circuits that reach the striatum from other brain areas, including the limbic cortex (associated with emotional processing); the ventral striatum (related to the processing of rewards), and other important motor regions involved in movement ( Alexander and Crutcher, 1990 ). Currently, striatal neuronal plasticity enables basal ganglia circuits to interact with other structures and thereby contribute to the processing of procedural memoryterm·def ( Haber et al., 2000 ).
The cerebellum is involved in the execution of movements and the perfection of motor agility needed proceduralterm·dom skillsterm. Damage to this area can impede one from relearning motor skillsterm and recent studies have linked it to the process of automating unconsciousterm skillsterm during the learningterm·dom phase ( Kreitzer, 2009 ).
The limbic system shares anatomical structures with a component of the neostriatum, which assumes primary responsibility for the control of procedural memoryterm·def. There is a special protein membrane associated with the limbic system that runs through the nucleus basalis. Thus, activation of brain regions that work together during the operation of procedural memoryterm·def can be followed through the protein membrane associated with the limbic system.
As a final note on procedural memoryterm·def, whereas earlier theories proposed a passive role whereby memories were shielded from interfering stimuli during sleep ( Vertes and Eastman, 2000 ; Vertes, 2004 ), current theories suggest a more active role in which memories undergo a process of consolidationterm during sleep ( Ellenbogen et al., 2006 ). Furthermore, in human beings, this process of consolidationterm is thought to contribute to the development of proceduralterm·dom knowledge, especially when it occurs right after the initial phase of memoryterm·dom acquisition ( Karni et al., 1994 ; Gais et al., 2000 ; Stickgold et al., 2000a , b ; Saywell and Taylor, 2008 ). Within the scope of motor skillsterm related to procedural memoryterm·def, there is evidence to show that there is no improvement in skillsterm if followed by short NREM sleep (stages 2–4 sleep), such as a short nap ( Walker et al., 2002 ). However, REM sleep (a sleep phase with an increased frequency and intensity of the so-called dream state) followed by a period of slow wave sleep has proven to be the most effective combination for procedural memoryterm·def consolidationterm, especially immediately following skillterm acquisition ( Siegel, 2001 ).
Associative Memoryterm·def: Classical and Operant Conditioningterm·mth Associative memoryterm·def refers to the storageterm and retrievalterm of information through association with other information. The acquisition of associative memoryterm·def is carried out with two types of conditioningterm·mth: classical conditioningterm·mth and operant conditioningterm·mth. Classical conditioningterm·mth is associativeterm·dom learningterm·dom between stimuli and behavior. Meanwhile, operant conditioningterm·mth is a form of learningterm·dom in which new behaviors develop in terms of their consequences. Associationist philosophers have also worked with the latter modelterm ( Hartley, 1749 ; Mill, 1829 ). We will look more closely at both.
The close association between two stimuli over time causes classical conditioningterm·mth: first a conditioned stimulus and then an unconditioned stimulus. While a conditioned stimulus does not automatically trigger a response, an unconditioned stimulus does just that. By repeating a conditioned stimulus over time before an unconditioned stimulus, a conditioned stimulus acquires characteristics that simulate being necessary for an unconditioned stimulus. Pavlov’s Dog ( Pavlov, 1927 ) is a clear example. The dog produces saliva when it detects the presence of food (unconditioned stimulus). If the sound of a bell goes off (conditioned stimulus) during the act of giving the dog food, the dog will associate the sound of the bell with the presence of food. In successively repeating this, the dog will associate the unconditioned stimulus with the conditioned stimulus, thus producing saliva when just hearing the bell.
Although Skinner is considered to be the originator of operant conditioningterm·mth, his research drew upon Thorndike’s law of effect. For operant conditioningterm·mth, as has already been mentioned, positive consequences following a behavior promote its repetition. Conversely, if the behavior involves negative consequences, the behavior will be repeated less. Thorndike (1932) called this conditioningterm·mth instrumental because it suggests that the behavior serves as a means to an end and emerges from trial and error. Skinner later coined the term that is now widely associated with this law of effect – reinforcement ( Skinner, 1938 ).
Non-associative Memoryterm·def: Habituation and Sensitization Non-associative memoryterm·def is one of three types of non-declarativeterm or implicitterm memoryterm·dom and refers to newly learned behavior through repeated exposure to an isolated stimulus.
New behavior can be classified into two processes: sensitization and habituation ( Alonso, 2008 ). Before delving into each process, it is worth noting that the simplicity in acquiring this type of memoryterm·dom has advanced knowledge of the learningterm·dom process. This is due to the fact that both animals and human beings have these two processes, such that it is very likely that, in this regard, they share a molecular biological basis. Kandel (1976) proposed a modelterm to explain habituation and sensitization’s operation mechanism. On one hand, for habituation, acetylcholine is progressively consumed, decreasing the effectiveness of the stimulus and thus the motor response. Furthermore, for sensitization, the presence of serotonin, secreted by another sensory nerve terminal, causes an excess of acetylcholine. Thus an enhanced motor response emerges. Let’s look at the two processes that take place in the acquisition of new behaviors— processes that are part of non-associative memoryterm·def, habituation and sensitization.
Habituation, in this context, is linked to repetition. The repetition of a stimulus leads to a decrease in its response, which is known as habituation. Repeated exposure to a stimulus serves to stop responding to potentially important, but situationally irrelevant stimuli. Habituation could be due to a process of synaptic depression as a result of repeated activation. Thus, habituation is thought to be related to a decrease in the efficiency of synaptic transmission, a decrease that may be caused by a conductivity change in the membrane of the stimulated neuron’s iconicterm·dom channels.
Unlike habituation, sensitization consists in an increase in response to a stimulus due to the repeated introduction thereof. Although the processes that produce sensitization are the same as those that produce habituation, sensitization’s effects are the opposite since it results in an increase of the original response. The process of sensitization may be due to a provision in transmission, whether it be presynaptic or postsynaptic.
Primingterm·dom Primingterm·dom, the fourth modality of non-declarativeterm or implicitterm memoryterm·dom, is an effect whereby exposure to certain stimuli influences the response given to stimuli presented later.
An example is in order. If you present a list of words to a person that contains the word ‘ball,’ and then the person is asked to participate in a task to complete words, they are more likely to respond with the word ball to the presentation of the word bowl than if they had not previously seen that word in the original list. Thus, the primingterm·dom capacityterm can affect the choice of a particular word on a test to complete words, even long after consciousterm recollection of the primed words has been forgotten.
Another context where this can be seen is in asking a participant to identify an image from a small fragment. The participant is shown a larger portion of the image over time, giving them the ability to identify the image at the end. The participant will take longer to identify the image if it is the first time he/she sees it. But if he/she already saw it in a previous trial, he/she takes less time ( Kolb and Whishaw, 2003 ).
Future Directions In spite of recent progress, a number of important questions remain to be tackled.
Many of these questions have to do with molecular processes of memoryterm·dom consolidationterm, retrievalterm, and decay. Take, for instance, the processes underlying the LTPterm of synaptic strength among neurons of the hippocampusterm·dom ( Dong et al., 2015 ). In their reviewterm·mth, Hardt et al. (2013) point out that while the “molecular processes involved in establishing LTPterm have been characterized well, the decay of early and late LTPterm is poorly understood.” One possibility that has recently been suggested is that LTPterm decay is mediated by AMPAR endocytosis, which in turn implies that inhibition of this process could preserve LTPterm and help to prevent memoryterm·dom loss ( Dong et al., 2015 ).
Other recent work shows the critical role of dopamine as a signal that promotes the stable incorporation of novel information into long-term hippocampal memoryterm·dom ( Otmakhova et al., 2013 ). Indeed, dopamine neurons can be activated by novelty in the absence of reward and it is thought that this activation occurs via a polysynaptic pathway that runs from the hippocampusterm·dom to the dopamine cells of the VTA. However, many aspects of this process remain unclear (see Otmakhova et al., 2013 ).
Also requiring further investigation are the molecular processes involved in the regulation of protein synthesis related to memoryterm·dom. It is now thought that protein synthesis is not only involved in the consolidationterm of new memories, but must also be used to re-consolidate memories that have been degraded or “destabilized” as a result of retrievalterm. In a recent article, Jarome et al. (2016) indicate that CaMKII controls the re-consolidation process through the regulation of proteasome activity. Another mechanism for the regulation of protein synthesis involves MicroRNAs (miRNAs), a class of short, non-coding RNAs. By regulating components of pathways required for learningterm·dom and memoryterm·dom, miRNAs modulate the influence of epigenetics on cognition in the normal and diseased brain ( Saab and Mansuy, 2014 ).
Another set of important questions relates to the long-standing hypothesis of “Hebbian learningterm·dom”—the strengthening of synapses between neurons with correlated activity—and its role in memoryterm·dom. At the same time that we are learningterm·dom more about the mechanisms involved in Hebbian plasticity, we are also learningterm·dom about how these mechanisms are complemented by synaptogenesis and neuromodulatory processes. Recent research has shown that synaptogenesis is not only important during development, but also plays a central role in associativeterm·dom learningterm·dom and memoryterm·dom. Synaptogenesis can be triggered by neuron–astrocyte or neuron–neuron contact, and mediated by cell-adhesion proteins including neurexin/neuroligin, Eph receptors, and cadherins, which activate intracellular signaling pathways involving cofilin, GTPases, and other proteins (for a reviewterm·mth see Nelson and Alkon, 2015 ). Others have proposed that Hebbian processes, while important, are not sufficient for memoryterm·dom formation, and must be supported by the activation of neuromodulatory processes, especially in the case of associativeterm·dom aversive learningterm·dom ( Johansen et al., 2014 ). Another study found evidence for both Hebbian and anti-Hebbian mechanisms of synaptic plasticity, indicating that the mechanisms of learningterm·dom are highly adaptable ( Koch et al., 2013 ).
Finally, other questions relate to the special role of the amygdalaterm in the emotional enhancement of memoryterm·dom consolidationterm. It has long been known that emotional arousal contributes to the selection and consolidationterm of memoryterm·dom. It has also been shown that previously weak or inconsequential information can be strengthened retroactively through an emotional learningterm·dom experience ( Dunsmoor et al., 2015 ). Evidence suggests that it is the amygdalaterm that is most responsible for the enhancement of memoryterm·dom ( de Voogd et al., 2016 ). As suggested by a reviewterm·mth, these developments “will likely lead to an updated view of the amygdalaterm as a critical nexus within large-scale networks supporting different aspects of memoryterm·dom processing for emotionally arousing experiences” ( Hermans et al., 2014 ). Moreover, this research is likely to have important implications for the treatment of psychological disorders ( Beckers and Kindt, 2017 ).
Conclusion and Glossaryterm There are three main forms of memoryterm·dom: sensory memoryterm·dom, short-term memoryterm·dom, and long-term memoryterm·dom ( Figure 3 ). Sensory memoryterm·dom refers to the retention of information coming from the senses. Short-term memoryterm·dom refers to information processed in a short period of time. Working memoryterm·dom performs this processing. Working memoryterm·dom consists of four elements that process information: the central executiveterm (attentionterm control), the visuospatialterm sketchpadterm (creates and maintains a visuospatialterm representation), the phonologicalterm buffer (stores and consolidates new words), and the episodic bufferterm (stores and integrates information from different sources). Long-term memoryterm·dom allows us to store information for long periods of time. This information may be retrieved consciously (explicit memoryterm·def) or unconsciously (implicitterm memoryterm·dom). Explicit memoryterm·def consists of episodicterm·dom memoryterm·dom (time-related events) and semanticterm·dom memoryterm·dom (concepts and meanings). Implicitterm memoryterm·dom has, in turn, procedural memoryterm·def (motor and executive skillsterm), associative memoryterm·def (classical and operant conditioningterm·mth), non-associative memoryterm·def (sensitization and habituation), and primingterm·dom (a primary stimulus influencing a secondary one).
FIGURE 3.
Memoryterm·dom classificationterm.
Finally, the following glossaryterm includes commentary about the terminologyterm that, in our opinion, is essential for an introductory overview, enabling interested students and professionals to effectively approach the latest memory-related discoveries. This commentary is not intended as an exhaustive definitionterm, but rather collects relevant information to situate the reader within a complex panorama.
Associative memoryterm·def : refers to the storageterm and retrievalterm of information resulting from an association (i.e., resulting from an association with other information). Two types of conditioningterm·mth are involved in its acquisition: classical conditioningterm·mth and operant conditioningterm·mth. Classical conditioningterm·mth is a kind of associativeterm·dom learningterm·dom between stimuli and behavior, and operant conditioningterm·mth is a form of learningterm·dom in which new behaviors develop in terms of their consequences.
Conceptual short-term memoryterm·dom/episodic bufferterm : This is a temporary storageterm system capable of integrating information from different sources that is probably controlled by the central executiveterm. It is episodicterm·dom in that it has episodes in which information is integrated through space and, potentially, extended through time.
Echoicterm·dom memoryterm·dom : sensory memoryterm·dom that receives and processes auditory information.
Episodicterm·dom memoryterm·dom : “involves the ability to learn, store, and retrieve information about unique personal experiences that occur in daily life. These memories typically include information about the time and place of an event, as well as detailed information about the event itself” ( Dickerson and Eichenbaum, 2010 ).
Explicitterm/declarativeterm memoryterm·dom : refers to consciousterm memories of previously stored experiences, facts and concepts that are verifiable through a verbal reporting of them ( Tulving, 1972 ).
Hapticterm·dom memoryterm·dom : sensory memoryterm·dom that receives and processes information from the sense of touch.
Iconic memoryterm·def : visual-sensory memoryterm·dom that receives and processes visual stimuli.
Implicitterm/non-declarativeterm memoryterm·dom : this encompasses all unconsciousterm memories, as well as certain abilities or skillsterm. There are four types of implicitterm memoryterm·dom: proceduralterm·dom, associativeterm·dom, non-associative, and primingterm·dom memoryterm·dom.
Long-term memoryterm·dom : “refers to the unlimited, continuing memoryterm·dom store that can hold information over lengthy periods of time, even for an entire lifetime. Long-term memoryterm·dom is mainly preconscious and unconsciousterm. Information in long-term memoryterm·dom is to a great extent outside of our awareness, but can be called into working memoryterm·dom to be used when needed. Some of this information is easy to recall, but some is much more difficult to access” ( Brodziak et al., 2013 ).
Non-associative memoryterm·def : refers to newly learned behavior due to repeated exposure to a single stimulus. The new behavior can be classified into two processes: sensitization and habituation.
Perceptual memoryterm·def : memoryterm·dom acquired through the senses. It includes a lot of individual experience; it ranges from the simplest forms of sensory memoryterm·dom to the most abstract knowledge.
Primingterm·dom : an effect whereby exposure to certain stimuli influences the response to subsequently presented stimuli.
Procedural memoryterm·def : a memoryterm·dom area involved in remembering executive and motor skillsterm necessary to perform a task. It is an executive system that guides activity and usually works on an unconsciousterm level. When necessary, proceduralterm·dom memories are automatically retrieved for use in the implementation of integrated procedures related to motor and intellectual skillsterm.
Semanticterm·dom memoryterm·dom : refers to the memoryterm·dom of meanings, interpretations and concepts related to facts, information and general knowledge about the world. Semanticterm·dom memoryterm·dom gives meaning to words and phrases that would otherwise be meaningless and allows for learningterm·dom based on past experience ( Kolb and Whishaw, 2003 ).
Sensory memoryterm·dom : “Sensory memoryterm·dom is the capacityterm for briefly retaining the large amounts of information that people encounter daily” ( Siegler and Alibali, 2005 ).
Short-term memoryterm·dom: is the ability to keep a small amount of information available for a short period of time. “Short-term memoryterm·dom should be distinguished from working memoryterm·dom, which refers to structures and processes used for temporarily storing and manipulating information. The relationship between short-term memoryterm·dom and working memoryterm·dom is presented variously by different theories. The notion of working memoryterm·dom is broader and more general because it refers to structures and processes used for temporarily stored and manipulated information” ( Brodziak et al., 2013 ).
Working memoryterm·dom : “The term working memoryterm·dom refers to a brain system that provides temporary storageterm and manipulation of the information necessary for such complex cognitive tasks as language comprehension, learningterm·dom and reasoning” ( Baddeley, 1992 ).
Visual memoryterm·dom : constituted by iconic memoryterm·def, visual short-term and long-term memoryterm·dom.
Visual short-term memoryterm·dom/visuospatialterm sketchpadterm : sketchpadterm’s main function is to create and maintain a visuospatialterm representation that persists through the irregular form found in eye movement and that characterizes our exploration of the visual world ( Luck, 2007 ).
Author Contributions FG drafting of sensory and short-term memoryterm·dom; bibliographical reviewterm·mth; introduction and conclusion. Revising critically and final approval of the version to be published. EC drafting of long-term memoryterm·dom (declarativeterm and non-declarativeterm); bibliographical reviewterm·mth.
Conflict of Interest Statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Acknowledgments This work was supported by the Institute for Culture and Society (ICS) of the University of Navarra and by the “Programa de Ayudas de la Asociación de Amigos de la Universidad de Navarra.” We are grateful to Mind-Brain Group of ICS and, especially, to Nathaniel Barrett Ph.D., Gonzalo Arrondo Ph.D., and Javier Bernácer Ph.D. for their suggestions.