Neural correlates of consciousness: progress and problems — TEI-tagged view

Koch, Massimini, Boly, Tononi · 2016 · neuroscience · doi:10.1038/nrn.2016.22 · full text at the source · TEI xml · tagged edition · index · concepts · authors
Where this record's text came from. faceted 2026-08 by reading the locally held text (pdftext); every evidence string verified as an exact substring of that text before merging. Claim type is 'existence' because the headline contribution is a localisation claim (the NCC are in the posterior hot zone, not fronto-parietal cortex); the paper is simultaneously a sustained critique of two candidate markers, which is captured in claim relations instead. Replication status is 'contested' because the paper itself records live disagreement on its central territory — no-report and lesion evidence against the fronto-parietal view, but it also notes 'However, other findings contradict this interpretation' regarding fronto-parietal candidacy, and describes the thalamus's role as controversial. Note on claim relations: this journal cites by superscript number, so no prior work is named in running text; the two relations recorded are ones the paper explicitly frames as a proposal it then rejects, and the targets are described rather than named. Relations to the earlier NRN review ('since the subject was last reviewed in this journal3') were left out for the same reason — the target is identified only by a citation number. 2026-08-14 schema-0.3 pass: every quote verified as an exact substring of the staged text and anchored at merge time; concept terms verified present; every edge endpoint an existing node.
1 quote on this page breaks a word across a line. The PDF this text was extracted from hyphenated a word at the end of a printed line — adversar- ial, repre- sentations — and the extractor kept the hyphen and the space. The quotes keep them because a quote is reproduced exactly or it proves nothing: the break is the typesetter’s, not the author’s. A search of this page will not find the affected words.
This record’s own method is review, and the tags below follow from that. A review’s findings, quantities and statistics are things stated IN this paper, and some of them report results obtained elsewhere. No tag on this page names a different author. Measured across every review in this corpus, 81% of a review’s tags carry no citation at all — most of them are the review speaking. The corpus does not adjudicate the rest: read an unmarked tag as a claim this paper makes, not necessarily one it made first.
Other fields define these differently the same word, defined another way in another discipline
consciousness 10 fields
Tags on this paper every tag the record carries, whether or not the words occur in the text below — a number is how many papers in the corpus carry that tag; a tag with no number is unique to this paper
full NCC contentspecific NCC gamma activity2 P3b wave behavioural responses consciousness20 review319

Our tag layer for this paper

Cross-disciplinary analysis
content-tags & facets: phenomenon · claim-type · cross-domain-transfer · mechanism · claim-relation · replication-status · limitation — grounded in the full text
phenomenonneural correlates of consciousness— “The NCC are defined as the minimum neuronal mechanisms jointly sufficient for any one specific conscious percept21,22.”
claim-typeexistence— “In this Review, we describe recent findings showing that the anatomical neural correlates of consciousness are primarily localized to a posterior cortical hot zone that includes sensory areas, rather than to a fronto-parietal network involved in task monitoring and reporting.”
method — evidence— “We also discuss some candidate neurophysiological markers of consciousness that have proved illusory, and measures of differentiation and integration of neural activity that offer more promising quantitative indices of consciousness.”
mechanismDiffusely projecting brainstem, hypothalamic and basal forebrain populations depolarize thalamic and cortical neurons, and this depolarization enables consciousness indirectly by making effective interactions between cortical areas possible.— “Rather, it is likely that the activity of hetero geneous neuronal populations within the brainstem, hypothalamus and basal forebrain, which project diffusely to thalamic and cortical neurons and promote their depolarization, provides an important background condition for enabling consciousness by facilitating effective interactions among…mechanisms[0]
mechanismFronto-parietal activity co-varies with reported perception because report-based tasks recruit attention, expectation, self-monitoring, planning and reporting, which precede or follow the experience rather than constituting it.— “It has become clear, however, that at least part of the neural activity that co-varies with the perception of a particular conscious content reflects processes that precede or follow the experience — such as selective attention, expectation, self-monitoring, unconscious stimulus processing, task planning and reporting29–32 — rather than the…mechanisms[1]
mechanismBrainstem reticular formation, paramedian thalamus and postero-medial cortex act as activating influences and cortical hubs, thereby enabling the interactions among the cortical areas that supply conscious content.— “By serving as activating influences and cortical hubs, they enable effective interactions among the cortical areas that directly contribute conscious content.”mechanisms[2]
contradicts the proposal that the P3b/global ignition of fronto-parietal cortex is a signature of consciousness (REF. 142)— “However, this interpretation has been contradicted by several experimental results.”claim_relations[0]
contradicts earlier proposals that gamma activity or synchrony, and the P3b event-related potential, are signatures of consciousness— “Regarding the neurophysiological markers of consciousness, hopes that gamma activity or synchrony, or the ERP P3b, could be signatures of consciousness have proved illusory (FIG. 3).”claim_relations[1]
sensethe NCC - ONE DEFINITION, TWO READINGS, FLAGGED BY ITS AUTHORS: the minimum neuronal mechanisms jointly sufficient for any one specific conscious percept, with the review stating there are two possible interpretations depending on whether the specific content or the state is meant; the definition does not determine its own referent— “The NCC are defined as the minimum neuronal mechanisms jointly sufficient for any one specific conscious percept21,22. There are two possible interpretations of this definition”senses[0]
sensethe full NCC - A UNION OVER A SET STILL BEING ENUMERATED: it is constituted by the union of all content-specific NCC, so the whole is complete exactly when the enumeration is, and the enumeration is the research programme itself— “The union of all such contentspecific NCC constitutes the full NCC”senses[1]
sensegamma activity and the P3b wave - CANDIDATE MARKERS WITHDRAWN: both were popular and neither has shown predictive power, so two named quantities that circulated as indices of consciousness are reported as failing the role— “We discuss how two popular candidate physiological markers of consciousness — gamma activity and the P3b wave — have not shown any predictive power”senses[2]
edgecontentspecific NCC —part-of→ full NCC— “The union of all such contentspecific NCC constitutes the full NCC”concept_edges[0]
effect directiongamma activity —causes→ consciousness — no-change— “We discuss how two popular candidate physiological markers of consciousness — gamma activity and the P3b wave — have not shown any predictive power”— “have not shown any predictive power”concept_edges[1]
effect directionP3b wave —causes→ consciousness — no-change— “We discuss how two popular candidate physiological markers of consciousness — gamma activity and the P3b wave — have not shown any predictive power”— “have not shown any predictive power”concept_edges[2]
for which uselimitation — the modality coverage of the review: THIS REVIEW FOCUSES ON VISUAL AND AUDITORY STUDIES; FOR ACCOUNTS OF THE NCC FOR METACOGNITION, BODY, TACTILE AND OLFACTORY EXPERIENCES, SEE REFS— “This Review focuses on visual and auditory studies; for accounts of the NCC for metacognition, body, tactile and olfactory experiences, see REFS 4–7.”limitations[0]
for which uselimitation — the empirical programme as a route to the question: WE OUTLINE THE INHERENT LIMITS OF SUCH AN EMPIRICAL RESEARCH PROGRAMME— “We outline the inherent limits of such an empirical research programme.”limitations[1]
for which uselimitation — every clinical, developmental, comparative and machine application: THE NCC BY THEMSELVES CAN PROVIDE LITTLE INFORMATION ABOUT CONSCIOUSNESS IN PATIENTS WITH SEVERE BRAIN DAMAGE, INFANTS, FETUSES, NON-HUMAN SPECIES OR INTELLIGENT MACHINES— “The NCC by themselves can provide little information about consciousness in patients with severe brain damage, infants, fetuses, non-human species or intelligent machines (BOX 1).”limitations[2]
for which uselimitation — the conclusion that V1 is outside the content-specific NCC: IT IS NOT KNOWN WHETHER THIS CONCLUSION APPLIES TO OTHER VISUAL ATTRIBUTES, SUCH AS PRECISE SPATIAL TOPOGRAPHY, LUMINOSITY AND DETAILED CONTOURS— “It is not known whether this conclusion applies to other visual attributes, such as precise spatial topography, lumin osity and detailed contours94–96.”limitations[3]
for which uselimitation — any use of the NCC as a single construct: the authors define it as the minimum neuronal mechanisms jointly sufficient for any one specific conscious percept, and state that there are two possible interpretations of that definition— “The NCC are defined as the minimum neuronal mechanisms jointly sufficient for any one specific conscious percept21,22. There are two possible interpretations of this definition”limitations[4]
for which uselimitation — any use of gamma activity or the P3b wave as a marker of consciousness: the authors state these two popular candidates have not shown any predictive power— “We discuss how two popular candidate physiological markers of consciousness — gamma activity and the P3b wave — have not shown any predictive power”limitations[5]
for which uselimitation — any inference from absent behaviour to absent consciousness: the authors state consciousness can be present even without reliable behavioural responses, and that minimally conscious patients can be misclassified as vegetative— “However, consciousness can be present even in the absence of reliable behavioural responses. For example, minimally conscious patients can be misclassified as being in a non-conscious, vegetative state, with significant clinical, practical and emotional consequences”limitations[6]
replicationcontested
limitationThe review restricts itself to visual and auditory studies and does not cover other modalities or metacognition.— “This Review focuses on visual and auditory studies; for accounts of the NCC for metacognition, body, tactile and olfactory experiences, see REFS 4–7.”limitations[0]
limitationThe authors state that the empirical NCC research programme has inherent limits.— “We outline the inherent limits of such an empirical research programme.”limitations[1]
limitationNCC evidence cannot settle whether consciousness is present in brain-damaged patients, infants, animals or machines.— “The NCC by themselves can provide little information about consciousness in patients with severe brain damage, infants, fetuses, non-human species or intelligent machines (BOX 1).”limitations[2]
limitationThe conclusion that V1 is not part of the content-specific NCC may not generalise to untested visual attributes.— “It is not known whether this conclusion applies to other visual attributes, such as precise spatial topography, lumin osity and detailed contours94–96.”limitations[3]
limitationThe field's central definition is stated by its own authors to admit two interpretations.— “The NCC are defined as the minimum neuronal mechanisms jointly sufficient for any one specific conscious percept21,22. There are two possible interpretations of this definition”limitations[4]
limitationTwo popular candidate markers are reported to have no predictive power.— “We discuss how two popular candidate physiological markers of consciousness — gamma activity and the P3b wave — have not shown any predictive power”limitations[5]
limitationConsciousness is stated to be possible without reliable behavioural responses, with the misclassification named.— “However, consciousness can be present even in the absence of reliable behavioural responses. For example, minimally conscious patients can be misclassified as being in a non-conscious, vegetative state, with significant clinical, practical and emotional consequences”limitations[6]
Content tags
content-observations: finding · quantity · variable · definition · key-term — grounded in the full text
findingBoth the full and the content-specific NCC sit in a restricted temporo-parieto-occipital posterior hot zone rather than in the wide fronto-parietal network that earlier work emphasised.— “The anatomical basis of the full NCC and contentspecific NCC do not comprise the wide fronto-parietal network emphasized in past studies, but are primarily localized to a more restricted temporo- parietal-occipital hot zone with additional contributions from some anterior regions (FIG. 2).”content_tags.findings[0]
findingParadigms in which participants make no overt report yield a narrower content-specific NCC that contains posterior cortical areas but excludes prefrontal cortex.— “Such no-report paradigms identify a more restricted content-specific NCC, which typically includes posterior cortical areas but not the prefrontal cortex.”content_tags.findings[1]
findingGamma synchrony survives or grows during early NREM sleep, anaesthesia and seizures and accompanies unconscious emotional stimuli, so it occurs without consciousness.— “Gamma synchrony can persist or even increase during early NREM sleep, during anaesthesia171,172 or during seizures173, and can be present during exposure to stimuli that induce unconscious emotional responses174, suggesting that gamma synchrony can occur in the absence of consciousness.”content_tags.findings[2]
findingThe P3b is missing in most clearly conscious brain-damaged patients and detects minimally conscious patients very poorly, so it fails as a signature of consciousness.— “In fact, the P3b is absent in the majority of patients with brain damage who remain clearly conscious182–184 and has minimal sensitivity (0.14) in identifying minimally conscious patients185.”content_tags.findings[3]
findingPrimary visual cortex V1 is not part of the content-specific NCC for any visual attribute tested so far.— “Taken together, the evidence discussed here supports the hypothesis that V1 is not part of the content-specific NCC for the attributes that have been tested so far.”content_tags.findings[4]
findingConsciousness survives removal of prefrontal cortex: complete bilateral frontal lobectomy and large bilateral prefrontal resections leave it intact.— “For example, complete bilateral frontal lobectomy123 and large bilateral prefrontal resections do not impair consciousness124.”content_tags.findings[5]
findingCerebellar lesions have little effect on consciousness and its contents.— “Lesions of the cerebellum have little effect on consciousness and its contents, however47.”content_tags.findings[6]
findingLocal rather than global EEG activation, especially over the posterior hot zone, may be what matters for consciousness.— “Thus, it may be that local, rather than global, EEG activation is important for consciousness, especially over the posterior cortical hot zone.”content_tags.findings[7]
findingThe perturbational complexity index is the first measure that tracks the level of consciousness across sleep stages, anaesthetics and disorders of consciousness and does so for individual participants.— “PCI is the first metric that successfully assesses the level of consciousness under different conditions (for example, during different sleep stages, during exposure to anaesthetics and in disorders of consciousness) and at the level of single participants (FIG. 4).”content_tags.findings[8]
findingNo single brain area turns out to be necessary for being conscious, though areas of the posterior cortical hot zone are the best candidates for both full and content-specific NCC.— “In short, no single brain area seems to be necessary for being conscious, but a few areas, especially in the posterior cortical hot zone, are good candidates for both full and content-specific NCC.”content_tags.findings[9]
quantity0.14 — sensitivity of the P3b for identifying minimally conscious patients— “In fact, the P3b is absent in the majority of patients with brain damage who remain clearly conscious182–184 and has minimal sensitivity (0.14) in identifying minimally conscious patients185.”content_tags.quantities[0]
quantity40% — proportion of unresponsive, sedated and hypothermic coma patients in whom multivariate decoding still finds a P3b-like component— “When this kind of analysis is applied, however, it is possible to find a P3b-like component in 40% of coma patients who are unresponsive, sedated and hypothermic187.”content_tags.quantities[1]
quantity143 — number of severely brain-injured patients with disorders of consciousness in the structural imaging study of thalamic atrophy— “In addition, structural imaging of 143 patients with severe brain injury and disorders of consciousness revealed no correlation between the level of arousal and thalamic atrophy, but did find a correlation between decreased motor function and/or the ability to communicate and thalamic atrophy57.”content_tags.quantities[2]
quantitymore than one-third — share of awakenings from NREM sleep after which participants report having been conscious, despite reduced neuromodulatory activity— “Indeed, when awakened from NREM sleep, when the activity of most neuromodulatory systems is reduced53, participants report having been conscious before being woken in more than one-third of instances54.”content_tags.quantities[3]
quantity>75 μV — amplitude threshold for the repeated EEG slow waves used to assess loss of consciousness in humans— “Detecting repeated high-amplitude slow waves (>75 μV) in the EEG is an effective way to assess the loss of consciousness in humans and is better than most available alternatives172,195.”content_tags.quantities[4]
quantity120– 140 ms — latency of cortical responses to visual stimuli attributed to a feedforward sweep from V1 to extrastriate and inferior temporal cortex— “Cortical neural responses to visual stimuli, such as natural scenes and faces, can occur quickly (within 120– 140 ms) and presumably are mediated by a feed forward volley through the V1 into the extrastriate cortex and inferior temporal cortex129–131.”content_tags.quantities[5]
quantityclose to 1 million — number of nerve cells in a bee brain, cited when asking whether insects can be conscious— “For example, bee brains contain close to 1 million nerve cells packed up to ten times more densely than in the neocortex and assembled in non-linear feedback circuits238.”content_tags.quantities[6]
definitionneural correlates of consciousness (NCC)— “The NCC are defined as the minimum neuronal mechanisms jointly sufficient for any one specific conscious percept21,22.”content_tags.definitions[0]
definitioncontent-specific NCC— “The content‑specific NCC are the neurons (or, more generally, neuronal mechanisms), the activity of which determines a particular phenomenal distinction within an experience.”content_tags.definitions[1]
definitionfull NCC— “The full NCC, as defined here, are the neural substrates supporting conscious experiences in their entirety, irrespective of their specific contents.”content_tags.definitions[2]
definitionbackground conditions for consciousness— “These are factors that enable consciousness without contributing directly to its content, such as appropriate glucose and oxygen levels, an appropriate neuromodulatory milieu and afferent inputs that ensure adequate cortical excitability.”content_tags.definitions[3]
definitionposterior cortical hot zone— “Because of this converging evidence, the posterior cortical region can be considered as a hot zone for the NCC.”content_tags.definitions[4]
definitionno-report paradigm— “This can be achieved by matching performance33, manipulating task relevance34 or using a no-report paradigm33,35 during which participants do not make any overt report, such as speaking or pushing a button (FIG. 1b).”content_tags.definitions[5]
definitionperturbational complexity index (PCI)— “The perturbational complexity index (PCI), obtained using a combination of TMS and EEG recordings219, assesses the level of consciousness based on the notion that being conscious requires both the differentiation and integration of cortical activity1,38.”content_tags.definitions[6]
definitionneuronal avalanches— “Neuronal avalanches — spatiotemporal patterns of spontaneous activity that reflect a critical state of network excitability favourable to information integration — only occur in supragranular layers155.”content_tags.definitions[7]
definitionP3b— “Another well-studied electrophysiological candidate marker of consciousness is a late (>300 ms after the onset of…content_tags.definitions[8]
Concepts
terms this paper carries, each with the sentence it was cut from — the layer that joins one paper to another. Terms with no quote yet are on CONCEPTS.html.
conceptfull NCCconcepts[0]
conceptcontentspecific NCCconcepts[1]
conceptgamma activityconcepts[2]
conceptP3b waveconcepts[3]
conceptbehavioural responsesconcepts[4]
conceptconsciousnessconcepts[5]

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