Consciousness and Anesthesia

Consciousness and Anesthesia Alkire Hudetz Tononi

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Consciousness and Anesthesia 2008 Science (New York, N.Y.) 10.1126/science.1149213 Alkire2008-consciousness-and-anesthesia Alkire2008-consciousness-and-anesthesia.txt, the project's staged copy 3bccdb69e35b075c259819c992430b855767734a not-redistributable neuroscience

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0 spans located by searching the stored text for the quote's exact words, allowing any whitespace between them how general anesthetics abolish consciousness, and whether the states they produce are unconsciousness or only unresponsiveness and amnesia Quotation withheld because this record is not cleared for redistribution. when we are anesthetized, does consciousness always vanish — and what neural change is the one that actually removes it Quotation withheld because this record is not cleared for redistribution. argues that anesthetics remove consciousness when they block the integration of information — either by disconnecting the posterior corticothalamic complex or by collapsing its repertoire of states — and that the field's behavioural test cannot tell unconsciousness from unresponsiveness Quotation withheld because this record is not cleared for redistribution. mechanism Quotation withheld because this record is not cleared for redistribution. anesthetic-induced unconsciousness Quotation withheld because this record is not cleared for redistribution. review review Quotation withheld because this record is not cleared for redistribution. mechanisms Anesthetics abolish consciousness by blocking the corticothalamic system's capacity to integrate information, not simply by silencing neurons Quotation withheld because this record is not cleared for redistribution. mechanisms Because the corticothalamic system is a small-world network, cutting only a few long-range connections fragments it into functionally disconnected components Quotation withheld because this record is not cleared for redistribution. mechanisms Deep anesthesia collapses the response repertoire into a stereotypic two-state burst-suppression regime, so activity carries almost no information even while remaining globally integrated Quotation withheld because this record is not cleared for redistribution. two independent routes to unconsciousness are proposed, so that a brain can fail either by disconnecting or by running out of things to say Quotation withheld because this record is not cleared for redistribution. burst-suppression is the crucial counterexample to activity-based accounts: the system is active, hyperexcitable and globally integrated, and still unconscious, because its repertoire has fallen to two states Quotation withheld because this record is not cleared for redistribution. a causal role for the thalamus is demoted to a readout by a timing argument: cortical EEG changes at the instant of loss of consciousness, thalamic EEG only ten minutes later Quotation withheld because this record is not cleared for redistribution. unresponsiveness is separated from unconsciousness by existence proofs rather than by measurement: dreaming and pharmacological paralysis are states with experience and without response Quotation withheld because this record is not cleared for redistribution. amnesia is separated from unconsciousness the same way: the isolated forearm technique buys a channel of report that survives paralysis, and patients use it and then deny having been awake Quotation withheld because this record is not cleared for redistribution. TMS is used as a perturbation probe: push the cortex and measure how far and how specifically the response travels, which turns integration into something measurable rather than inferred from correlation Quotation withheld because this record is not cleared for redistribution. convergence across two unrelated ways of losing consciousness — anesthesia and slow-wave sleep — is what carries the argument, since neither alone would isolate the common factor Quotation withheld because this record is not cleared for redistribution. network topology explains the disproportion between a small pharmacological insult and a total loss of consciousness: in a small-world graph a few long-range edges hold the whole thing together Quotation withheld because this record is not cleared for redistribution. lesion data and anesthesia data are used as mutual corroboration, on the argument that a drug and a knife reaching the same region should produce the same deficit Quotation withheld because this record is not cleared for redistribution. a theory is used to license a negative rule of inference, forbidding both directions of the usual behavioural reading Quotation withheld because this record is not cleared for redistribution. the die metaphor is doing real theoretical work, not decoration: it makes 'integration' and 'information' visibly separable — a die that disintegrates versus a die that is flattened Quotation withheld because this record is not cleared for redistribution. The integrated-information measure the paper's framework rests on cannot at present be computed for real brains, only for small simulated systems. what this limits: every quantitative use of the integrated-information framework: IN PRACTICE, PHI CAN ONLY BE MEASURED RIGOROUSLY FOR SMALL, SIMULATED SYSTEMS - not for the brains the theory is about Quotation withheld because this record is not cleared for redistribution. The paper cannot settle which component of the posterior complex matters most, nor the role of anterior cortex. what this limits: any anatomical localisation drawn from the review: WHETHER THE MEDIAL OR LATERAL COMPONENT IS MORE IMPORTANT, AND WHETHER ANTERIOR CORTICAL REGIONS ARE CRITICAL ... RE[mains open] Quotation withheld because this record is not cleared for redistribution. the measure the theory rests on cannot be computed for a brain duplicate of: limitations[0] · what this limits: the same scope as limitations[0] - the measure the framework rests on cannot be computed for a brain Quotation withheld because this record is not cleared for redistribution. the paper opens by conceding that the thing it is explaining the loss of is itself unexplained what this limits: everything the review explains: HOW CONSCIOUSNESS ARISES IN THE BRAIN REMAINS UNKNOWN, so the loss is described without the thing being lost being understood Quotation withheld because this record is not cleared for redistribution. which part of the posterior complex matters is left open what this limits: the same scope as limitations[1] - which part of the posterior complex matters is left open Quotation withheld because this record is not cleared for redistribution. the existing monitors fail exactly where they are needed, at the transition what this limits: the clinical monitors: THEY REMAIN LIMITED AT DIRECTLY INDICATING THE PRESENCE OR ABSENCE OF CONSCIOUSNESS, ESPECIALLY AROUND THE TRANSITION POINT - which is where they are needed Quotation withheld because this record is not cleared for redistribution. a disjunction the paper cannot resolve: the signal may be wrong, or the interpretation may be what this limits: any EEG-based correlate: EITHER THE EEG IS NOT SENSITIVE ENOUGH TO THE NEURAL PROCESSES UNDERLYING CONSCIOUSNESS, OR WE STILL DO NOT YET FULLY UNDERSTAND WHAT TO LOOK FOR Quotation withheld because this record is not cleared for redistribution. the candidate region is deactivated in REM sleep, when experience is vivid — the paper states the counterexample to its own anatomy without resolving it what this limits: the deactivation-equals-unconsciousness account: MESIAL CORTICAL AREAS ARE DEACTIVATED IN REM SLEEP, WHEN SUBJECTS EXPERIENCE VIVID DREAMS Quotation withheld because this record is not cleared for redistribution. selective deactivation of the candidate posterior region produces altered experience, not absent experience what this limits: the same scope as limitations[7], from the clinical side: WHEN THESE AREAS START TO TURN OFF, SUBJECTS REPORT DREAMLIKE FEELINGS WITH DEPERSONALIZATION AND OUT OF BODY EXPERIENCES, RATHER THAN UNCONSCIOUSNESS Quotation withheld because this record is not cleared for redistribution. the classical measurement of information as reduction of uncertainty in bits, applied to brain states and conscious experience Quotation withheld because this record is not cleared for redistribution. the bit and the reduction of uncertainty among alternatives, imported wholesale as the measure of how much experience a brain state constitutes Quotation withheld because this record is not cleared for redistribution. small-world topology, used to explain why a small pharmacological insult to a few long-range connections can fragment the whole system Quotation withheld because this record is not cleared for redistribution. transfer entropy, borrowed as a directional measure so that feedforward and feedback interactions can be scored separately Quotation withheld because this record is not cleared for redistribution. the die as a model of a state repertoire, extended so that losing integration shatters it into many dice and losing information flattens it to two faces Quotation withheld because this record is not cleared for redistribution. integration integration Quotation withheld because this record is not cleared for redistribution. information information Quotation withheld because this record is not cleared for redistribution. burst-suppression burst-suppression Quotation withheld because this record is not cleared for redistribution. unconsciousness — behavioural sense: failing to move on command, the 160-year-old clinical criterion Quotation withheld because this record is not cleared for redistribution. unconsciousness — experiential sense: absence of experience, which the behavioural criterion does not track Quotation withheld because this record is not cleared for redistribution. information — classical sense: reduction of uncertainty among alternatives, measured in bits Quotation withheld because this record is not cleared for redistribution. information — the paper's working sense: the number of discriminable activity patterns a neural system can produce Quotation withheld because this record is not cleared for redistribution. integration — the ability of different cortical regions to interact effectively, explicitly flagged as a loose definition Quotation withheld because this record is not cleared for redistribution. consciousness — graded, increasing with the repertoire of discriminable states, not all-or-none Quotation withheld because this record is not cleared for redistribution. thalamus — as a switch that gates consciousness, versus as a readout of cortical state; the paper names both and argues for the second Quotation withheld because this record is not cleared for redistribution. down-state — local, induced under one TMS site, versus global, induced across the connectional core; the same term at two scales in one paragraph Quotation withheld because this record is not cleared for redistribution. anesthetics — two classes by clinical role: intravenous agents to induce, volatile agents to maintain Quotation withheld because this record is not cleared for redistribution. loss of consciousness — as an abrupt threshold crossing, versus as a shrinking or dimming; the paper says the evidence shows both Quotation withheld because this record is not cleared for redistribution. claim_type: mechanism a second reading reaching the same value. Recorded: mechanism — note: a second reading reaching the same value from a different sentence. Not applied - a person decides. Quotation withheld because this record is not cleared for redistribution. method: narrative review — pharmacological, neuroimaging, lesion, EEG and TMS evidence read together and against a theory, with no new data a second reading DIFFERING from the recorded value. Recorded: review — note: a second reading, verbatim-verified, disagreeing with the value on the record. Not applied - a person decides. Quotation withheld because this record is not cleared for redistribution. phenomenon: loss of consciousness under general anesthesia a second reading DIFFERING from the recorded value. Recorded: anesthetic-induced unconsciousness — note: a second reading, verbatim-verified, disagreeing with the value on the record. Not applied - a person decides. Quotation withheld because this record is not cleared for redistribution. critiques → the behavioural definition of unconsciousness that anesthesia has used since its introduction Quotation withheld because this record is not cleared for redistribution. critiques → the thalamic switch hypothesis (ref 2), that the thalamus gates consciousness differs in: READOUT AGAINST SWITCH - the axis is what role the thalamus plays, not whether it is involved. 'the effects of anesthetics on the thalamus effect Quotation withheld, and thalamic activity may not be a sufficient basis for consciousness.' The thalamic-switch hypothesis is not denied its data; it is denied its causal direction. Quotation withheld because this record is not cleared for redistribution. supports → the integrated information theory of consciousness (ref 52) Quotation withheld because this record is not cleared for redistribution. contradicts → the clinical inference from absent motor response to absent consciousness Quotation withheld because this record is not cleared for redistribution. extends → existing depth-of-anesthesia monitoring, by proposing monitors that measure integration and information separately Quotation withheld because this record is not cleared for redistribution. supports → rival frameworks — global workspace and coalitions of neurons — which the paper declines to argue against Quotation withheld because this record is not cleared for redistribution. unresponsiveness —distinct-from→ unconsciousness unresponsiveness unconsciousness strength of the relation: 0.95 Quotation withheld because this record is not cleared for redistribution. EVIDENCE CORRECTED (RE-GROUNDED) · amnesia —distinct-from→ unconsciousness amnesia unconsciousness EVIDENCE CORRECTED: RE-GROUNDED. The old span named only unconsciousness. This sentence names both and distinguishes them ON THE EVIDENCE AVAILABLE FOR EACH - anaesthesia 'undoubtedly induces ... amnesia' while the extent to which it causes unconsciousness 'is harder to establish'. — strength of the relation: 0.95 Audit 2026-09-28: DOUBTFUL - read against its full span and kept, but the span says anesthesia induces amnesia while its extent of causing unconsciousness is harder to establish; distinct-from is implied, not stated. Quotation withheld because this record is not cleared for redistribution. integrated information —operationalised-as→ phi integrated information phi strength of the relation: 0.95 Quotation withheld because this record is not cleared for redistribution. integration —operationalised-as→ transfer entropy integration transfer entropy strength of the relation: 0.85 Audit 2026-09-28: DOUBTFUL - read against its span and kept, but the span names transfer entropy as a measure of directional interactions; operationalising integration is a loose reading. Quotation withheld because this record is not cleared for redistribution. thalamus —distinct-from→ consciousness switch thalamus consciousness switch differs in: THE AXIS IS CAUSAL DIRECTION. 'the effects of anesthetics on the thalamus effect Quotation withheld, and thalamic activity may not be a sufficient basis for consciousness.' The thalamic data are not disputed; what is disputed is whether the thalamus DRIVES the state or REPORTS it. · strength of the relation: 0.75 Audit 2026-09-28: DOUBTFUL - read against its full span and kept, but the thalamic effect 'MAY represent' a readout rather than a consciousness switch; distinct-from is hedged. Quotation withheld because this record is not cleared for redistribution. burst-suppression —causes→ information burst-suppression information direction on the measure: reduces · the relation itself is separately evidenced · strength of the relation: 0.8 · the relation stated: the collapse to burst-suppression carries a LOSS OF information - two states where there were many Audit 2026-09-28: DOUBTFUL - read against its span and kept, but the span is a fragment ('with a corresponding loss of information'); the cause is not in it. Quotation withheld because this record is not cleared for redistribution. up-state —distinct-from→ down-state up-state down-state strength of the relation: 0.95 Quotation withheld because this record is not cleared for redistribution. corticothalamic system —is-a→ small-world corticothalamic system small-world strength of the relation: 0.85 Quotation withheld because this record is not cleared for redistribution. cerebellum —contrasted-with→ corticothalamic system cerebellum corticothalamic system strength of the relation: 0.9 Audit 2026-09-28: DOUBTFUL - read against its full span and kept, but endpoint by anaphora: 'By contrast' = the corticothalamic complex (previous sentence). Quotation withheld because this record is not cleared for redistribution. depth of anesthesia —operationalised-as→ bispectral index depth of anesthesia bispectral index strength of the relation: 0.85 Quotation withheld because this record is not cleared for redistribution. global workspace —distinct-from→ integrated information global workspace integrated information strength of the relation: 0.7 Audit 2026-09-28: DOUBTFUL - read against its full span and kept, but the span says other frameworks such as the global workspace are ALSO CONSISTENT with the findings; distinct-from is loose. Quotation withheld because this record is not cleared for redistribution. propofol —contrasted-with→ thiopental propofol thiopental strength of the relation: 0.8 Quotation withheld because this record is not cleared for redistribution. slow wave sleep —contrasted-with→ anesthesia slow wave sleep anesthesia strength of the relation: 0.8 Audit 2026-09-28: DOUBTFUL - read against its span and kept, but the span says anesthesia is not the same as natural sleep; the endpoint 'slow wave sleep' is narrower. Quotation withheld because this record is not cleared for redistribution. mesial cortical areas —part-of→ default network mesial cortical areas default network strength of the relation: 0.75 Quotation withheld because this record is not cleared for redistribution. Most anesthetic agents appear to cause unconsciousness by acting, directly or indirectly, on a posterior lateral corticothalamic complex around the inferior parietal lobe, and perhaps a medial cortical core. Quotation withheld because this record is not cleared for redistribution. The thalamic effects of anesthetics may be a readout of global cortical activity rather than a consciousness switch. Quotation withheld because this record is not cleared for redistribution. Behavioural unresponsiveness under anesthesia does not reliably indicate that the patient is unconscious. Quotation withheld because this record is not cleared for redistribution. Post-operative amnesia is likewise not evidence that the patient was unconscious during surgery. Quotation withheld because this record is not cleared for redistribution. Evidence from both anesthesia and sleep converges on two routes to unconsciousness: loss of cortical integration or collapse of the repertoire of cortical activity patterns. Quotation withheld because this record is not cleared for redistribution. On the integrated-information account, consciousness is graded rather than all-or-none, scaling with the size of a system's repertoire of discriminable states. Quotation withheld because this record is not cleared for redistribution. intraoperative awareness occurs about once in every 1000–2000 operations Quotation withheld because this record is not cleared for redistribution. sevoflurane sedation cuts relative thalamic metabolism by 23% while subjects are still awake and responsive Quotation withheld because this record is not cleared for redistribution. cortical EEG changed at the instant of loss of consciousness while thalamic EEG did not change for another ten minutes Quotation withheld because this record is not cleared for redistribution. in REM sleep the two dissociate the other way: cortical EEG activated as if awake, thalamic EEG showing slow waves as if asleep Quotation withheld because this record is not cleared for redistribution. after thalamic ablation the cortex still produces an activated EEG Quotation withheld because this record is not cleared for redistribution. the thalamic effects of anesthetics in animals disappear when the cortex is removed Quotation withheld because this record is not cleared for redistribution. ketamine raises global metabolism, especially in the thalamus Quotation withheld because this record is not cleared for redistribution. at equivalent hypnotic doses propofol and thiopental both deactivate posterior areas, but only propofol deactivates frontal cortex Quotation withheld because this record is not cleared for redistribution. large frontal lesions do not by themselves produce unconsciousness Quotation withheld because this record is not cleared for redistribution. a clinically unresponsive woman with large frontal lesions produced cortical activation patterns indistinguishable from healthy subjects when asked to imagine playing tennis Quotation withheld because this record is not cleared for redistribution. as consciousness fades, EEG coherence in the gamma range drops between the two frontal cortices and between frontal and occipital regions Quotation withheld because this record is not cleared for redistribution. the coherence loss is far stronger for long-range than for local connections Quotation withheld because this record is not cleared for redistribution. in rats losing responsiveness, information transfer falls in the feedback direction first Quotation withheld because this record is not cleared for redistribution. anesthesia suppresses the late component of visual responses but not the early feedforward one, and abolishes contextual and attentional modulation Quotation withheld because this record is not cleared for redistribution. in early non-REM sleep a TMS pulse produces only a short (<150 ms) local response, suggesting a loss of integration Quotation withheld because this record is not cleared for redistribution. TMS to mesial parietal cortex, over the main connectional hub, triggers a stereotypic high-amplitude slow wave closely resembling a spontaneous one Quotation withheld because this record is not cleared for redistribution. nitrous oxide at intermediate doses selectively deactivates posterior mesial cortex, yet subjects report dreamlike experience rather than none Quotation withheld because this record is not cleared for redistribution. generalized convulsive seizures abolish consciousness even though neural activity is high and hypersynchronous, because that activity is stereotypic Quotation withheld because this record is not cleared for redistribution. GABA agonists injected into the intralaminar nuclei make rats fall asleep, and a nicotine injection there awakens rats under sevoflurane Quotation withheld because this record is not cleared for redistribution. computer simulations show a rapid state transition at a critical anesthetic dose, consistent with a breakdown of network integration Quotation withheld because this record is not cleared for redistribution. patients can be aware and responsive during surgery while the bispectral index says otherwise Quotation withheld because this record is not cleared for redistribution. integrated information integrated information Quotation withheld because this record is not cleared for redistribution. large-scale integration large-scale integration Quotation withheld because this record is not cleared for redistribution. hyperkinetic mutism hyperkinetic mutism Quotation withheld because this record is not cleared for redistribution. small-world networks small-world networks Quotation withheld because this record is not cleared for redistribution. burst-suppression pattern burst-suppression pattern Quotation withheld because this record is not cleared for redistribution. integration integration Quotation withheld because this record is not cleared for redistribution. information information Quotation withheld because this record is not cleared for redistribution. phi phi Quotation withheld because this record is not cleared for redistribution. burst-suppression burst-suppression Quotation withheld because this record is not cleared for redistribution. Small-world networks Small-world networks Quotation withheld because this record is not cleared for redistribution. transfer entropy transfer entropy Quotation withheld because this record is not cleared for redistribution. isolated forearm technique isolated forearm technique Quotation withheld because this record is not cleared for redistribution. hyperkinetic mutism hyperkinetic mutism Quotation withheld because this record is not cleared for redistribution. electroencephalogram (EEG) electroencephalogram (EEG) Quotation withheld because this record is not cleared for redistribution. down-state down-state Quotation withheld because this record is not cleared for redistribution. flat EEG flat EEG Quotation withheld because this record is not cleared for redistribution. information information Quotation withheld because this record is not cleared for redistribution. once in every 1000–2000 operations — rate at which a surgical patient regains or retains consciousness under general anesthesia (intraoperative awareness) Quotation withheld because this record is not cleared for redistribution. 23% — reduction of relative thalamic metabolism under sevoflurane sedation in subjects who are still awake and responsive, showing thalamic suppression is not sufficient for unconsciousness Quotation withheld because this record is not cleared for redistribution. once in every 1000–2000 operations — rate of intraoperative awareness Quotation withheld because this record is not cleared for redistribution. over 160 years — age of the behavioural definition of unconsciousness Quotation withheld because this record is not cleared for redistribution. 23% — reduction of relative thalamic metabolism under sevoflurane sedation in awake responsive subjects Quotation withheld because this record is not cleared for redistribution. 10 minutes — lag between the cortical EEG change at loss of consciousness and any thalamic change Quotation withheld because this record is not cleared for redistribution. 20 to 80 Hz — gamma range in which coherence drops as consciousness fades Quotation withheld because this record is not cleared for redistribution. 20 to 60 Hz — gamma range of the flash-evoked response in rat occipital cortex Quotation withheld because this record is not cleared for redistribution. 300 ms — duration of the sequential TMS-evoked response during wakefulness Quotation withheld because this record is not cleared for redistribution. <150 ms — duration of the local TMS-evoked response in early non-REM sleep Quotation withheld because this record is not cleared for redistribution. >100 ms — the late visual response component that anesthesia suppresses Quotation withheld because this record is not cleared for redistribution. 1 Hz or less — frequency of the slow oscillation between up- and down-states in slow wave sleep Quotation withheld because this record is not cleared for redistribution. roughly once a second — rate of up/down oscillation at intermediate anesthetic concentrations Quotation withheld because this record is not cleared for redistribution. a tenth of a second or more — duration of the synaptic silence in the down-state Quotation withheld because this record is not cleared for redistribution. 1.1% isoflurane — anesthetic concentration in the rat flash-response experiment Quotation withheld because this record is not cleared for redistribution. 0.2 Hz — rate of the flashing light stimulus Quotation withheld because this record is not cleared for redistribution. 1 bit — information from a two-sided outcome, the coin and the flattened die Quotation withheld because this record is not cleared for redistribution. ~2.6 bits — information from a six-faced die Quotation withheld because this record is not cleared for redistribution. a trillion faces — the scale of the experiential repertoire in the paper's metaphor Quotation withheld because this record is not cleared for redistribution. transfer entropy transfer entropy Quotation withheld because this record is not cleared for redistribution. phi (Φ) phi (Φ) Quotation withheld because this record is not cleared for redistribution. EEG coherence EEG coherence Quotation withheld because this record is not cleared for redistribution. bits bits Quotation withheld because this record is not cleared for redistribution. current density current density Quotation withheld because this record is not cleared for redistribution. bispectral index bispectral index Quotation withheld because this record is not cleared for redistribution. thalamic metabolism thalamic metabolism Quotation withheld because this record is not cleared for redistribution. EEG coherence EEG coherence Quotation withheld because this record is not cleared for redistribution. transfer entropy transfer entropy Quotation withheld because this record is not cleared for redistribution. depth of anesthesia depth of anesthesia Quotation withheld because this record is not cleared for redistribution. anesthetic dose anesthetic dose Quotation withheld because this record is not cleared for redistribution. repertoire of discriminable states repertoire of discriminable states Quotation withheld because this record is not cleared for redistribution. field potentials field potentials Quotation withheld because this record is not cleared for redistribution. functional connectivity functional connectivity Quotation withheld because this record is not cleared for redistribution.

The full text of this article is not redistributable, so it is not included here. The evidence sentences are withheld with it; the tag layer and its grounding status remain. The article itself is at https://doi.org/10.1126/science.1149213.