Editing Consciousness (section)

==Scientific study==
For many decades, consciousness as a research topic was avoided by the majority of mainstream scientists, because of a general feeling that a phenomenon defined in subjective terms could not properly be studied using objective experimental methods.<ref>{{cite book|author=Horst Hendriks-Jansen|title=Catching ourselves in the act: situated activity, interactive emergence, evolution, and human thought|year=1996|publisher=Massachusetts Institute of Technology|page=114|isbn=978-0-262-08246-4}}</ref> In 1975 [[George Mandler]] published an influential psychological study which distinguished between slow, serial, and limited conscious processes and fast, parallel and extensive unconscious ones.<ref>Mandler, G. "Consciousness: Respectable, useful, and probably necessary". In R. Solso (Ed.) ''Information processing and cognition'': NJ: LEA.</ref> The Science and Religion Forum<ref>{{Cite web|date=2021|title=Science and Religion Forum|url=https://www.srforum.org/about|url-status=live |archive-url=https://web.archive.org/web/20161103075415/http://srforum.org/about/|archive-date=2016-11-03}}</ref> 1984 annual conference, '''From Artificial Intelligence to Human Consciousness''<nowiki/>' identified the nature of consciousness as a matter for investigation; [[Donald Michie]] was a keynote speaker. Starting in the 1980s, an expanding community of neuroscientists and psychologists have associated themselves with a field called ''Consciousness Studies'', giving rise to a stream of experimental work published in books,<ref>Mandler, G. Consciousness recovered: Psychological functions and origins of thought. Philadelphia: John Benjamins. 2002</ref> journals such as ''[[Consciousness and Cognition]]'', ''Frontiers in Consciousness Research'', ''[[Psyche (consciousness journal)|Psyche]]'', and the ''[[Journal of Consciousness Studies]]'', along with regular conferences organized by groups such as the [[Association for the Scientific Study of Consciousness]]<ref>{{cite book|title=Toward a Science of Consciousness III: The Third Tucson Discussions and Debates|author=Stuart Hameroff|author2=Alfred Kaszniak|author3-link=David Chalmers|author3=David Chalmers|chapter=Preface|isbn=978-0-262-58181-3|publisher=MIT Press|year=1999|pages=xix–xx|author-link=Stuart Hameroff}}</ref> and the [[Society for Consciousness Studies]].

Modern medical and psychological investigations into consciousness are based on psychological experiments (including, for example, the investigation of [[Priming (psychology)|priming]] effects using [[subliminal stimuli]]),<ref>Lucido, R. J. (2023). Testing the consciousness causing collapse interpretation of quantum mechanics using subliminal primes derived from random fluctuations in radioactive decay. Journal of Consciousness Exploration & Research, 14(3), 185-194. https://doi.org/10.13140/RG.2.2.20344.72969</ref> and on [[case studies]] of alterations in consciousness produced by trauma, illness, or drugs. Broadly viewed, scientific approaches are based on two core concepts. The first identifies the content of consciousness with the experiences that are reported by human subjects; the second makes use of the concept of consciousness that has been developed by neurologists and other medical professionals who deal with patients whose behavior is impaired. In either case, the ultimate goals are to develop techniques for assessing consciousness objectively in humans as well as other animals, and to understand the neural and psychological mechanisms that underlie it.<ref name=KochQuest/>

===Measurement via verbal report===
[[File:Necker cube.svg|thumb|upright|The [[Necker cube]], an ambiguous image]]

Experimental research on consciousness presents special difficulties, due to the lack of a universally accepted [[operational definition]]. In the majority of experiments that are specifically about consciousness, the subjects are human, and the criterion used is verbal report: in other words, subjects are asked to describe their experiences, and their descriptions are treated as observations of the contents of consciousness.<ref>{{cite book|author=Bernard Baars|title=A Cognitive Theory of Consciousness|year=1993|publisher=Cambridge University Press|isbn=978-0-521-42743-2| pages=15–18|author-link=Bernard Baars}}</ref>

For example, subjects who stare continuously at a [[Necker cube]] usually report that they experience it "flipping" between two 3D configurations, even though the stimulus itself remains the same.<ref>{{cite book|title=Perception: Theory, Development, and Organization|author=Paul Rooks|author2=Jane Wilson|year=2000|publisher=Psychology Press|isbn=978-0-415-19094-7|pages=25–26}}</ref> The objective is to understand the relationship between the conscious awareness of stimuli (as indicated by verbal report) and the effects the stimuli have on brain activity and behavior. In several paradigms, such as the technique of [[response priming]], the behavior of subjects is clearly influenced by stimuli for which they report no awareness, and suitable experimental manipulations can lead to increasing priming effects despite decreasing prime identification (double dissociation).<ref name="Schmidt">{{cite journal|author=Thomas Schmidt|author2=Dirk Vorberg|title=Criteria for unconscious cognition: Three types of dissociation|journal=Perception and Psychophysics|volume=68|year=2006|pages=489–504|doi=10.3758/bf03193692|pmid=16900839|issue=3|doi-access=free}}</ref>

Verbal report is widely considered to be the most reliable indicator of consciousness, but it raises a number of issues.<ref name="Destrebecqz" /> For one thing, if verbal reports are treated as observations, akin to observations in other branches of science, then the possibility arises that they may contain errors—but it is difficult to make sense of the idea that subjects could be wrong about their own experiences, and even more difficult to see how such an error could be detected.<ref>{{cite book|chapter=Quining qualia|author=Daniel Dennett|title=Consciousness in Modern Science|editor=A. Marcel|editor2=E. Bisiach|publisher=Oxford University Press|year=1992|chapter-url=http://cogprints.org/254/|access-date=2011-10-31|isbn=978-0-19-852237-9|author-link=Daniel Dennett|archive-date=2011-10-28|archive-url=https://web.archive.org/web/20111028195212/http://cogprints.org/254/|url-status=live}}</ref> Daniel Dennett has argued for an approach he calls [[heterophenomenology]], which means treating verbal reports as stories that may or may not be true, but his ideas about how to do this have not been widely adopted.<ref>{{cite journal|author=Daniel Dennett|year=2003|title=Who's on first? Heterophenomenology explained|journal=Journal of Consciousness Studies|volume=10|pages=19–30|author-link=Daniel Dennett}}</ref> Another issue with verbal report as a criterion is that it restricts the field of study to humans who have language: this approach cannot be used to study consciousness in other species, pre-linguistic children, or people with types of brain damage that impair language. As a third issue, philosophers who dispute the validity of the [[Turing test]] may feel that it is possible, at least in principle, for verbal report to be dissociated from consciousness entirely: a philosophical zombie may give detailed verbal reports of awareness in the absence of any genuine awareness.<ref>{{cite book|author=David Chalmers|title=The Conscious Mind|chapter-url=https://archive.org/details/consciousmindins00chal|chapter-url-access=registration|year=1996|chapter=Ch. 3: Can consciousness be reductively explained?|publisher=Oxford University Press|isbn=978-0-19-511789-9|author-link=David Chalmers}}</ref>

Although verbal report is in practice the "gold standard" for ascribing consciousness, it is not the only possible criterion.<ref name="Destrebecqz">{{cite book|title=The Boundaries of Consciousness: Neurobiology and Neuropathology|chapter=Methods for studying unconscious learning|author=Arnaud Destrebecqz|author2=Philippe Peigneux|editor=Steven Laureys|year=2006|publisher=Elsevier|isbn=978-0-444-52876-6|pages=69–80}}</ref> In medicine, consciousness is assessed as a combination of verbal behavior, arousal, brain activity, and purposeful movement. The last three of these can be used as indicators of consciousness when verbal behavior is absent.<ref name="Giacino" /><ref>{{cite journal|title=How to Make a Consciousness Meter|date=October 2017|journal=Scientific American|volume=317|issue=5|pages=28–33|doi=10.1038/scientificamerican1117-28|author=Christof Koch|pmid=29565878|bibcode=2017SciAm.317e..28K}}</ref> The [[scientific literature]] regarding the neural bases of arousal and purposeful movement is very extensive. Their reliability as indicators of consciousness is disputed, however, due to numerous studies showing that alert human subjects can be induced to behave purposefully in a variety of ways in spite of reporting a complete lack of awareness.<ref name="Schmidt" /> Studies related to the [[neuroscience of free will]] have also shown that the influence consciousness has on decision-making is not always straightforward.<ref>{{cite journal|title=Human volition: towards a neuroscience of will|author=Patrick Haggard|journal=Nature Reviews Neuroscience|year=2008|volume=9|pages=934–946|pmid=19020512|doi=10.1038/nrn2497|issue=12|s2cid=1495720}}</ref>

==== Mirror test and contingency awareness ====
{{Also see|Mirror test}}

[[File:Mirror Test on Octopus vulgaris.jpg|thumb|[[Mirror test]] subjected on a [[common octopus]]]]

Another approach applies specifically to the study of [[self-awareness]], that is, the ability to distinguish oneself from others. In the 1970s [[Gordon G. Gallup|Gordon Gallup]] developed an operational test for self-awareness, known as the [[mirror test]]. The test examines whether animals are able to differentiate between seeing themselves in a mirror versus seeing other animals. The classic example involves placing a spot of coloring on the skin or fur near the individual's forehead and seeing if they attempt to remove it or at least touch the spot, thus indicating that they recognize that the individual they are seeing in the mirror is themselves.<ref>{{cite journal|author=Gordon Gallup|title=Chimpanzees: Self recognition|journal=Science|volume=167|pages=86–87|year=1970|doi=10.1126/science.167.3914.86|pmid=4982211|issue=3914|bibcode=1970Sci...167...86G|s2cid=145295899|author-link=Gordon G. Gallup}}</ref> Humans (older than 18 months) and other [[Hominidae|great apes]], [[bottlenose dolphin]]s, [[orca]]s, [[Columbidae|pigeons]], [[Eurasian magpie|European magpies]] and [[elephants]] have all been observed to pass this test.<ref>{{cite journal |author=David Edelman |author2=Anil Seth |year=2009 |title=Animal consciousness: a synthetic approach |journal=Trends in Neurosciences |volume=32 |issue=9 |pages=476–484 |doi=10.1016/j.tins.2009.05.008 |pmid=19716185 |s2cid=13323524}}</ref> While some other animals like [[pig]]s have been shown to find food by looking into the mirror.<ref>{{Cite journal |last1=Broom |first1=Donald M. |last2=Sena |first2=Hilana |last3=Moynihan |first3=Kiera L. |date= 2009|title=Pigs learn what a mirror image represents and use it to obtain information |url=https://linkinghub.elsevier.com/retrieve/pii/S0003347209003571 |journal=Animal Behaviour |language=en |volume=78 |issue=5 |pages=1037–1041 |doi=10.1016/j.anbehav.2009.07.027}}</ref>

Contingency awareness is another such approach, which is basically the conscious understanding of one's actions and its effects on one's environment.<ref>{{Cite web |title=Contingency Awareness - TalkSense |url=https://talksense.weebly.com/contingency-awareness.html#:~:text=Contingency%20Awareness%20(often%20referred%20to,actions%20elicit%20in%20the%20environment. |access-date=8 October 2024 |website=Weebly}}</ref> It is recognized as a factor in self-recognition. The brain processes during contingency awareness and learning is believed to rely on an intact [[medial temporal lobe]] and age. A study done in 2020 involving [[Transcranial direct-current stimulation|transcranial direct current stimulation]], [[Magnetic resonance imaging]] (MRI) and eyeblink classical conditioning supported the idea that the [[Parietal lobe|parietal cortex]] serves as a substrate for contingency awareness and that age-related disruption of this region is sufficient to impair awareness.<ref>{{Cite journal |last1=Cheng |first1=Dominic T. |last2=Katzenelson |first2=Alyssa M. |last3=Faulkner |first3=Monica L. |last4=Disterhoft |first4=John F. |last5=Power |first5=John M. |last6=Desmond |first6=John E. |date=4 March 2020 |title=Contingency awareness, aging, and the parietal lobe |journal=Neurobiology of Aging |language=en |volume=91 |pages=125–135 |doi=10.1016/j.neurobiolaging.2020.02.024 |pmc=7953809 |pmid=32241582}}</ref>

===Neural correlates===
[[File:Neural Correlates Of Consciousness.jpg|thumb|upright=1.6|{{center|Schema of the neural processes underlying consciousness, from [[Christof Koch]]}}]]

A major part of the scientific literature on consciousness consists of studies that examine the relationship between the experiences reported by subjects and the activity that simultaneously takes place in their brains—that is, studies of the [[neural correlates of consciousness]]. The hope is to find that activity in a particular part of the brain, or a particular pattern of global brain activity, which will be strongly predictive of conscious awareness. Several brain imaging techniques, such as [[EEG]] and [[fMRI]], have been used for physical measures of brain activity in these studies.<ref>{{cite book|author=Christof Koch|year=2004|title=The Quest for Consciousness|location=Englewood, CO|publisher=Roberts & Company|isbn=978-0-9747077-0-9|pages=16–19|author-link=Christof Koch}}</ref>

Another idea that has drawn attention for several decades is that consciousness is associated with high-frequency (gamma band) [[neural oscillations|oscillations in brain activity]]. This idea arose from proposals in the 1980s, by Christof von der Malsburg and Wolf Singer, that gamma oscillations could solve the so-called [[binding problem]], by linking information represented in different parts of the brain into a unified experience.<ref>{{cite journal|title=Binding by synchrony|author=Wolf Singer|journal=[[Scholarpedia]]|volume=2|issue=12|pages=1657|doi=10.4249/scholarpedia.1657|year=2007|bibcode=2007SchpJ...2.1657S|doi-access=free|s2cid=34682132}}</ref> [[Rodolfo Llinás]], for example, proposed that consciousness results from [[recurrent thalamo-cortical resonance]] where the specific thalamocortical systems (content) and the non-specific (centromedial thalamus) thalamocortical systems (context) interact in the [[gamma wave|gamma]] band frequency via synchronous oscillations.<ref>{{cite book|author=Rodolfo Llinás|year=2002|title=I of the vortex: from neurons to self|publisher=MIT Press|isbn=978-0-262-62163-2|author-link=Rodolfo Llinás|title-link=I of the vortex: from neurons to self}}</ref>

A number of studies have shown that activity in primary sensory areas of the brain is not sufficient to produce consciousness: it is possible for subjects to report a lack of awareness even when areas such as the [[primary visual cortex|primary visual cortex (V1)]] show clear electrical responses to a stimulus.<ref>Koch, ''The Quest for Consciousness'', pp. 105–116</ref> Higher brain areas are seen as more promising, especially the [[prefrontal cortex]], which is involved in a range of higher cognitive functions collectively known as [[executive functions]].<ref>{{Cite journal|last1=Baldauf|first1=D.|last2=Desimone|first2=R.|date=2014-04-25|title=Neural Mechanisms of Object-Based Attention|journal=Science|language=en|volume=344|issue=6182|pages=424–427|doi=10.1126/science.1247003|pmid=24763592|bibcode=2014Sci...344..424B|s2cid=34728448|issn=0036-8075|doi-access=free}}</ref> There is substantial evidence that a "top-down" flow of neural activity (i.e., activity propagating from the frontal cortex to sensory areas) is more predictive of conscious awareness than a "bottom-up" flow of activity.<ref>{{cite journal|title=A framework for consciousness|author=Francis Crick|author2=Christof Koch|year=2003|journal=Nature Neuroscience|volume=6|pages=119–126|pmid=12555104|url=http://papers.klab.caltech.edu/29/1/438.pdf|doi=10.1038/nn0203-119|issue=2|s2cid=13960489|url-status=dead|archive-url=https://web.archive.org/web/20120522054447/http://papers.klab.caltech.edu/29/1/438.pdf|archive-date=2012-05-22|author2-link=Christof Koch|author-link=Francis Crick}}</ref> The prefrontal cortex is not the only candidate area, however: studies by [[Nikos Logothetis]] and his colleagues have shown, for example, that visually responsive neurons in parts of the [[temporal lobe]] reflect the visual perception in the situation when conflicting visual images are presented to different eyes (i.e., bistable percepts during binocular rivalry).<ref>Koch, ''The Quest for Consciousness'', pp. 269–286</ref> Furthermore, top-down feedback from higher to lower visual brain areas may be weaker or absent in the peripheral visual field, as suggested by some experimental data and theoretical arguments;<ref name="Zhaoping-2019">{{Cite journal|last=Zhaoping|first=Li|date=2019-10-01|title=A new framework for understanding vision from the perspective of the primary visual cortex|url=https://psyarxiv.com/ds34j/download|journal=Current Opinion in Neurobiology|series=Computational Neuroscience|volume=58|pages=1–10|doi=10.1016/j.conb.2019.06.001|pmid=31271931|s2cid=195806018|issn=0959-4388|access-date=2022-03-02}}</ref> nevertheless humans can perceive visual inputs in the peripheral visual field arising from bottom-up V1 neural activities.<ref name="Zhaoping-2019" /><ref name="Zhaoping-2020">{{Cite journal|last=Zhaoping|first=Li|date=2020-07-30|title=The Flip Tilt Illusion: Visible in Peripheral Vision as Predicted by the Central-Peripheral Dichotomy|journal=i-Perception|volume=11|issue=4|pages=2041669520938408|doi=10.1177/2041669520938408|issn=2041-6695|pmc=7401056|pmid=32782769}}</ref> Meanwhile, bottom-up V1 activities for the central visual fields can be vetoed, and thus made invisible to perception, by the top-down feedback, when these bottom-up signals are inconsistent with the brain's internal model of the visual world.<ref name="Zhaoping-2019" /><ref name="Zhaoping-2020" />

Modulation of neural responses may correlate with phenomenal experiences. In contrast to the raw electrical responses that do not correlate with consciousness, the modulation of these responses by other stimuli correlates surprisingly well with an important aspect of consciousness: namely with the phenomenal experience of stimulus intensity (brightness, contrast). In the research group of Danko Nikolić it has been shown that some of the changes in the subjectively perceived brightness correlated with the modulation of firing rates while others correlated with the modulation of neural synchrony.<ref>{{cite journal|author1=Biederlack J.|author2=Castelo-Branco M.|author3=Neuenschwander S.|author4=Wheeler D.W.|author5=Singer W.|author6=Nikolić D.|year = 2006|title = Brightness induction: Rate enhancement and neuronal synchronization as complementary codes|journal = Neuron|volume = 52|issue = 6| pages = 1073–1083|doi=10.1016/j.neuron.2006.11.012|pmid=17178409|s2cid=16732916|doi-access=free}}</ref> An fMRI investigation suggested that these findings were strictly limited to the primary visual areas.<ref>{{cite journal|author1=Williams Adrian L.|author2=Singh Krishna D.|author3=Smith Andrew T.|year = 2003|title = Surround modulation measured with functional MRI in the human visual cortex|journal = Journal of Neurophysiology|volume = 89|issue = 1| pages = 525–533|doi=10.1152/jn.00048.2002|pmid=12522199|citeseerx=10.1.1.137.1066}}</ref> This indicates that, in the primary visual areas, changes in firing rates and synchrony can be considered as neural correlates of qualia—at least for some type of qualia.

In 2013, the perturbational complexity index (PCI) was proposed, a measure of the algorithmic complexity of the electrophysiological response of the cortex to [[transcranial magnetic stimulation]]. This measure was shown to be higher in individuals that are awake, in REM sleep or in a locked-in state than in those who are in deep sleep or in a vegetative state,<ref>{{cite journal|author1=Adenauer G. Casali|author2=Olivia Gosseries|author3=Mario Rosanova|author4=Mélanie Boly|author5=Simone Sarasso|author6=Karina R. Casali|author7=Silvia Casarotto|author8=Marie-Aurélie Bruno|author9=Steven Laureys|author10-link=Giulio Tononi|author10=Giulio Tononi|author11=Marcello Massimini|title=A Theoretically based index of consciousness independent of sensory processing and behavior|journal=Science Translational Medicine|date=14 August 2013|volume=5|number=198|pages=198ra105|doi=10.1126/scitranslmed.3006294|pmid=23946194|hdl=2268/171542|s2cid=8686961|url=http://orbi.ulg.ac.be/jspui/handle/2268/171542|hdl-access=free}}{{Dead link|date=June 2023|bot=InternetArchiveBot|fix-attempted=yes}}</ref> making it potentially useful as a quantitative assessment of consciousness states.

Assuming that not only humans but even some non-mammalian species are conscious, a number of evolutionary approaches to the problem of neural correlates of consciousness open up. For example, assuming that birds are conscious—a common assumption among neuroscientists and ethologists due to the extensive cognitive repertoire of birds—there are comparative neuroanatomical ways to validate some of the principal, currently competing, mammalian consciousness–brain theories. The rationale for such a comparative study is that the avian brain deviates structurally from the mammalian brain. So how similar are they? What homologs can be identified? The general conclusion from the study by Butler, et al.<ref name=Butler2005>{{cite journal|author1=Ann B. Butler|author2=Paul R. Manger|author3=B.I.B Lindahl|author4=Peter Århem|year=2005|title=Evolution of the neural basis of consciousness: a bird-mammal comparison|journal=BioEssays|volume=27|issue=9|pages=923–936|doi=10.1002/bies.20280|pmid=16108067}}</ref> is that some of the major theories for the mammalian brain<ref name=Crick1995>{{cite journal|author=[[Francis Crick]] and [[Christof Koch]]|year=1995|title=Are we aware of neural activity in primary visual cortex?|journal=Nature|volume=375|pages=121–123|doi=10.1038/375121a0|pmid=7753166|issue=6527| bibcode=1995Natur.375..121C|s2cid=4262990}}</ref><ref name=Edelman2000>{{cite book| author=[[Gerald Edelman|Gerald M. Edelman]] and [[Giulio Tononi]]|year=2000|title=A Universe of Consciousness: How Matter Becomes Imagination|publisher=Basic Books|isbn=978-0-465-01376-0}}</ref><ref name=Cotterill2001>{{cite journal|author=Rodney M.J. Cotterill|title=Cooperation of the basal ganglia, cerebellum, sensory cerebrum and hippocampus: possible implications for cognition, consciousness, intelligence and creativity|journal=Progress in Neurobiology|year=2001|volume=64|issue=1|pages=1–33|doi=10.1016/s0301-0082(00)00058-7|pmid=11250060|s2cid=206054149}}</ref> also appear to be valid for the avian brain. The structures assumed to be critical for consciousness in mammalian brains have homologous counterparts in avian brains. Thus the main portions of the theories of [[Francis Crick|Crick]] and [[Christof Koch|Koch]],<ref name="Crick1995"/> Edelman and [[Giulio Tononi|Tononi]],<ref name="Edelman2000"/> and Cotterill<ref name="Cotterill2001"/> seem to be compatible with the assumption that birds are conscious. Edelman also differentiates between what he calls primary consciousness (which is a trait shared by humans and non-human animals) and higher-order consciousness as it appears in humans alone along with human language capacity.<ref name="Edelman2000"/> Certain aspects of the three theories, however, seem less easy to apply to the hypothesis of avian consciousness. For instance, the suggestion by Crick and Koch that layer 5 neurons of the mammalian brain have a special role, seems difficult to apply to the avian brain, since the avian homologs have a different morphology. Likewise, the theory of [[John Eccles (neurophysiologist)|Eccles]]<ref>{{cite journal| year=1982|author=J.C. Eccles|title=Animal consciousness and human self-consciousness|journal=Experientia|volume=38|issue=12|pages=1384–1391|doi=10.1007/bf01955747|pmid=7151952|s2cid=35174442|author-link=John Eccles (neurophysiologist)}}</ref><ref>{{cite journal| year=1990|author=John Eccles|title=A unitary hypothesis of mind-brain interaction in the cerebral cortex|journal=Proceedings of the Royal Society of London B|volume=240|issue=1299|pages=433–451|doi=10.1098/rspb.1990.0047|pmid=2165613|bibcode=1990RSPSB.240..433E|s2cid=23188208|author-link=John Eccles (neurophysiologist)}}</ref> seems incompatible, since a structural homolog/analogue to the dendron has not been found in avian brains. The assumption of an avian consciousness also brings the reptilian brain into focus. The reason is the structural continuity between avian and reptilian brains, meaning that the phylogenetic origin of consciousness may be earlier than suggested by many leading neuroscientists.

[[Joaquin Fuster]] of UCLA has advocated the position of the importance of the prefrontal cortex in humans, along with the areas of Wernicke and Broca, as being of particular importance to the development of human language capacities neuro-anatomically necessary for the emergence of higher-order consciousness in humans.<ref>Joaquin Fuster, ''The Prefrontal Cortex'', Second Edition.</ref>

A study in 2016 looked at lesions in specific areas of the brainstem that were associated with [[coma]] and vegetative states. A small region of the rostral dorsolateral [[pontine tegmentum]] in the brainstem was suggested to drive consciousness through functional connectivity with two cortical regions, the left ventral [[anterior insular cortex]], and the pregenual [[anterior cingulate cortex]]. These three regions may work together as a triad to maintain consciousness.<ref>{{Cite journal|last1=Fischer|first1=David B.|last2=Boes|first2=Aaron D.|last3=Demertzi|first3=Athena|last4=Evrard|first4=Henry C.|last5=Laureys|first5=Steven|last6=Edlow|first6=Brian L.|last7=Liu|first7=Hesheng|last8=Saper|first8=Clifford B.|last9=Pascual-Leone|first9=Alvaro|last10=Fox|first10=Michael D.|last11=Geerling|first11=Joel C.|date=2016-12-06|title=A human brain network derived from coma-causing brainstem lesions|journal=Neurology|language=en|volume=87|issue=23|pages=2427–2434|doi=10.1212/WNL.0000000000003404|issn=0028-3878|pmid=27815400|pmc=5177681}}</ref>

===Models===
{{Further|Models of consciousness}}

A wide range of empirical theories of consciousness have been proposed.<ref name="northoff-lamme-2020">{{cite journal|last1=Northoff|first1=Georg|last2=Lamme|first2=Victor|title=Neural signs and mechanisms of consciousness: Is there a potential convergence of theories of consciousness in sight?|journal=Neuroscience and Biobehavioral Reviews|date=2020|volume=118|pages=568–587|doi=10.1016/j.neubiorev.2020.07.019|pmid=32783969|s2cid=221084519}}</ref><ref name="seth-bayne-2022">{{cite journal|last1=Seth|first1=Anil K.|last2=Bayne|first2=Tim|title=Theories of consciousness|journal=Nature Reviews Neuroscience|date=2022|volume=23|issue=7|pages=439–452|doi=10.1038/s41583-022-00587-4|pmid=35505255|s2cid=242810797|url=http://sro.sussex.ac.uk/id/eprint/105030/1/SethBayne_NRN_accepted.pdf|access-date=2023-01-17|archive-date=2023-01-21|archive-url=https://web.archive.org/web/20230121221104/http://sro.sussex.ac.uk/id/eprint/105030/1/SethBayne_NRN_accepted.pdf|url-status=live}}</ref><ref name="doerig-et-al-2021">{{cite journal|last1=Doerig|first1=Adrian|last2=Schurger|first2=Aaron|last3=Herzog|first3=Michael H.|title=Hard criteria for empirical theories of consciousness|journal=Cognitive Neuroscience|date=2021|volume=12|issue=2|pages=41–62|doi=10.1080/17588928.2020.1772214|pmid=32663056|s2cid=220529998|doi-access=free|hdl=2066/228876|hdl-access=free}}</ref> Adrian Doerig and colleagues list 13 notable theories,<ref name="doerig-et-al-2021"/> while [[Anil Seth]] and Tim Bayne list 22 notable theories.<ref name="seth-bayne-2022"/>

==== Global workspace theory ====
[[Global workspace theory]] (GWT) is a [[cognitive architecture]] and theory of consciousness proposed by the cognitive psychologist [[Bernard Baars]] in 1988. Baars explains the theory with the metaphor of a theater, with conscious processes represented by an illuminated stage. This theater integrates inputs from a variety of unconscious and otherwise autonomous networks in the brain and then broadcasts them to unconscious networks (represented in the metaphor by a broad, unlit "audience"). The theory has since been expanded upon by other scientists including cognitive neuroscientist [[Stanislas Dehaene]] and [[Lionel Naccache]].<ref name="baars-2005">{{cite book |last1=Baars |first1=Bernard J. |title=The Boundaries of Consciousness: Neurobiology and Neuropathology |year=2005 |isbn=9780444518514 |series=Progress in Brain Research |volume=150 |pages=45–53 |chapter=Global workspace theory of consciousness: Toward a cognitive neuroscience of human experience |citeseerx=10.1.1.456.2829 |doi=10.1016/S0079-6123(05)50004-9 |pmid=16186014}}</ref><ref name="dehaene-naccache">{{cite journal|last1=Dehaene|first1=Stanislas|last2=Naccache|first2=Lionel|title=Towards a cognitive neuroscience of consciousness: basic evidence and a workspace framework|journal=Cognition|date=2001|volume=79|issue=1–2|pages=1–37|url=http://zoo.cs.yale.edu/classes/cs671/12f/12f-papers/dehaene-consciousness.pdf|access-date=5 April 2019|doi=10.1016/S0010-0277(00)00123-2|pmid=11164022|s2cid=1762431|archive-date=13 July 2019|archive-url=https://web.archive.org/web/20190713125127/http://zoo.cs.yale.edu/classes/cs671/12f/12f-papers/dehaene-consciousness.pdf|url-status=live}}</ref>

==== Integrated information theory ====
[[Integrated information theory]] (IIT), pioneered by neuroscientist [[Giulio Tononi]] in 2004, postulates that consciousness resides in the information being processed and arises once the information reaches a certain level of complexity. Additionally, IIT is one of the only leading theories of consciousness that attempts to create a 1:1 mapping between conscious states and precise, formal mathematical descriptions of those mental states. Proponents of this model suggest that it may provide a physical grounding for consciousness in neurons, as they provide the mechanism by which information is integrated. This also relates to the "[[hard problem of consciousness]]" proposed by [[David Chalmers]]. The theory remains controversial, because of its lack of credibility.{{clarify|date=October 2024}}<ref name="nature.com">{{Cite journal |last1=Tononi |first1=Giulio |last2=Boly |first2=Melanie |last3=Massimini |first3=Marcello |last4=Koch |first4=Christof |date=July 2016 |title=Integrated information theory: from consciousness to its physical substrate |url=https://www.nature.com/articles/nrn.2016.44 |url-status=live |journal=Nature Reviews Neuroscience |language=en |volume=17 |issue=7 |pages=450–461 |doi=10.1038/nrn.2016.44 |issn=1471-0048 |pmid=27225071 |s2cid=21347087 |url-access=subscription |archive-url=https://web.archive.org/web/20230504082713/https://www.nature.com/articles/nrn.2016.44 |archive-date=2023-05-04 |access-date=2023-05-21}}</ref><ref>{{Cite journal |last=Lenharo |first=Mariana |date=2023-09-20 |title=Consciousness theory slammed as 'pseudoscience' — sparking uproar |url=https://www.nature.com/articles/d41586-023-02971-1 |journal=Nature |language=en |doi=10.1038/d41586-023-02971-1|pmid=37730789}}</ref><ref name=":0" />

==== Orchestrated objective reduction ====
[[Orchestrated objective reduction]] (Orch-OR), or the quantum theory of mind, was proposed by scientists [[Roger Penrose]] and [[Stuart Hameroff]], and states that consciousness originates at the quantum level inside neurons. The mechanism is held to be a quantum process called objective reduction that is orchestrated by cellular structures called [[microtubule]]s, which form the cytoskeleton around which the brain is built. The duo proposed that these quantum processes accounted for creativity, innovation, and problem-solving abilities. Penrose published his views in the book ''[[The Emperor's New Mind]]''. In 2014, the discovery of quantum vibrations inside microtubules gave new life to the argument.<ref name=":0" />

==== Attention schema theory ====
In 2011, [[Michael Graziano|Graziano]] and Kastner<ref name="Graziano&Kastner2011">{{cite journal|author1=Graziano, M.S.A.|author2=Kastner, S|year=2011|title=Human consciousness and its relationship to social neuroscience: A novel hypothesis|journal=Cog. Neurosci|volume=2|issue=2|pages=98–113|doi=10.1080/17588928.2011.565121|pmid=22121395|pmc=3223025}}</ref> proposed the [[attention schema theory|"attention schema" theory of awareness]]. In that theory, specific cortical areas, notably in the superior temporal sulcus and the temporo-parietal junction, are used to build the construct of awareness and attribute it to other people. The same cortical machinery is also used to attribute awareness to oneself. Damage to these cortical regions can lead to deficits in consciousness such as [[hemispatial neglect]]. In the [[attention]] schema theory, the value of explaining the feature of awareness and attributing it to a person is to gain a useful predictive model of that person's attentional processing. [[Attention]] is a style of [[Information processing (psychology)|information processing]] in which a brain focuses its resources on a limited set of interrelated signals. Awareness, in this theory, is a useful, simplified schema that represents attentional states. To be aware of X is explained by constructing a model of one's attentional focus on X.

==== Entropic brain theory ====
The entropic brain is a theory of conscious states informed by neuroimaging research with [[psychedelic drugs]]. The theory suggests that the brain in primary states such as [[Rapid eye movement sleep|rapid eye movement]] (REM) sleep, early [[psychosis]] and under the influence of psychedelic drugs, is in a disordered state; normal waking consciousness constrains some of this freedom and makes possible [[metacognitive]] functions such as internal self-administered [[reality testing]] and [[self-awareness]].<ref>{{cite journal|last1=Carhart-Harris|first1=R. L.|author1-link=Robin Carhart-Harris|last2=Friston|first2=K. J.|last3=Barker|first3=Eric L.|title=REBUS and the Anarchic Brain: Toward a Unified Model of the Brain Action of Psychedelics|journal=Pharmacological Reviews|date=20 June 2019|volume=71|issue=3|pages=316–344|doi=10.1124/pr.118.017160|pmid=31221820|pmc=6588209}}</ref><ref>{{cite journal|last1=Carhart-Harris|first1=Robin L.|title=The entropic brain – revisited|journal=Neuropharmacology|date=November 2018|volume=142|pages=167–178|doi=10.1016/j.neuropharm.2018.03.010|pmid=29548884|s2cid=4483591}}</ref><ref>{{cite journal|last1=Carhart-Harris|first1=Robin L.|last2=Leech|first2=Robert|last3=Hellyer|first3=Peter J.|last4=Shanahan|first4=Murray|last5=Feilding|first5=Amanda|last6=Tagliazucchi|first6=Enzo|last7=Chialvo|first7=Dante R.|last8=Nutt|first8=David|title=The entropic brain: a theory of conscious states informed by neuroimaging research with psychedelic drugs|journal=Frontiers in Human Neuroscience|date=2014|volume=8|pages=20|doi=10.3389/fnhum.2014.00020|pmid=24550805|pmc=3909994|doi-access=free}}</ref><ref>{{Cite web|url = https://mind-foundation.org/entropy-as-more-than-chaos/|title = Entropy as More than Chaos in the Brain: Expanding Field, Expanding Minds|date = 2018-06-22|access-date = 2019-07-05|archive-date = 2019-07-05|archive-url = https://web.archive.org/web/20190705111205/https://mind-foundation.org/entropy-as-more-than-chaos/|url-status = live}}</ref> Criticism has included questioning whether the theory has been adequately tested.<ref>{{cite journal|last1=Papo|first1=David|title=Commentary: The entropic brain: a theory of conscious states informed by neuroimaging research with psychedelic drugs|journal=Frontiers in Human Neuroscience|date=30 August 2016|volume=10|pages=423|doi=10.3389/fnhum.2016.00423|pmid=27624312|pmc=5004455|doi-access=free}}</ref>

==== Projective consciousness model ====
In 2017, work by David Rudrauf and colleagues, including [[Karl Friston]], applied the [[active inference]] paradigm to consciousness, leading to the projective consciousness model (PCM), a model of how sensory data is integrated with priors in a process of projective transformation. The authors argue that, while their model identifies a key relationship between computation and phenomenology, it does not completely solve [[the hard problem of consciousness]] or completely close the [[explanatory gap]].<ref>{{cite journal|author1=David Rudrauf|author2=Daniel Bennequin|author3=Isabela Granic|author4=Gregory Landini|author5=Karl Friston|author6=[[Kenneth Williford]]|year = 2017|title = A Mathematical Model of Embodied Consciousness|journal = Journal of Theoretical Biology|volume = 428|issue = 1| pages = 106–131|doi=10.1016/j.jtbi.2017.05.032|pmid=28554611|bibcode=2017JThBi.428..106R|s2cid=4476538|url=https://discovery.ucl.ac.uk/id/eprint/10057795/|hdl=2066/175365|hdl-access=free}}</ref>

==== Claustrum being the conductor for consciousness ====
In 2004, a proposal was made by molecular biologist [[Francis Crick]] (co-discoverer of the double helix), which stated that to bind together an individual's experience, a conductor of an orchestra is required. Together with neuroscientist [[Christof Koch]], he proposed that this conductor would have to collate information rapidly from various regions of the brain. The duo reckoned that the [[claustrum]] was well suited for the task. However, Crick died while working on the idea.<ref name=":0" />

The proposal is backed by a study done in 2014, where a team at the [[George Washington University]] induced unconsciousness in a 54-year-old woman suffering from [[Epilepsy|intractable epilepsy]] by stimulating her claustrum. The woman underwent depth electrode implantation and electrical stimulation mapping. The electrode between the left claustrum and anterior-dorsal insula was the one which induced unconsciousness. Correlation for interactions affecting medial parietal and posterior frontal channels during stimulation increased significantly as well. Their findings suggested that the left claustrum or anterior insula is an important part of a network that subserves consciousness, and that disruption of consciousness is related to increased [[Electroencephalography|EEG]] signal synchrony within frontal-parietal networks. However, this remains an isolated, hence inconclusive study.<ref name=":0" /><ref>{{Cite journal |last1=Koubeissi |first1=Mohamad Z. |last2=Bartolomei |first2=Fabrice |last3=Beltagy |first3=Abdelrahman |last4=Picard |first4=Fabienne |date= 2014|title=Electrical stimulation of a small brain area reversibly disrupts consciousness|url=https://linkinghub.elsevier.com/retrieve/pii/S1525505014002017 |journal=[[Epilepsy & Behavior]] |language=en |volume=37 |pages=32–35 |doi=10.1016/j.yebeh.2014.05.027|pmid=24967698}}</ref>

===Biological function and evolution===
The emergence of consciousness during [[Evolution|biological evolution]] remains a topic of ongoing scientific inquiry. The survival value of consciousness is still a matter of exploration and understanding. While consciousness appears to play a crucial role in human cognition, decision-making, and self-awareness, its adaptive significance across different species remains a subject of debate.

Some people question whether consciousness has any survival value. Some argue that consciousness is a [[Spandrel (biology)|by-product of evolution]]. [[Thomas Henry Huxley]] for example defends in an essay titled "On the Hypothesis that Animals are [[Automata]], and its History" an [[epiphenomenalist]] theory of consciousness, according to which consciousness is a causally inert effect of neural activity—"as the steam-whistle which accompanies the work of a locomotive engine is without influence upon its machinery".<ref>{{cite journal|author=T.H. Huxley|title=On the hypothesis that animals are automata, and its history|journal=The Fortnightly Review|volume=16|issue=253|pages=555–580|year=1874|author-link=T.H. Huxley|bibcode=1874Natur..10..362.|doi=10.1038/010362a0|doi-access=free}}</ref> To this [[William James]] objects in his essay ''Are We Automata?'' by stating an evolutionary argument for mind-brain interaction implying that if the preservation and development of consciousness in the biological evolution is a result of [[natural selection]], it is plausible that consciousness has not only been influenced by neural processes, but has had a survival value itself; and it could only have had this if it had been efficacious.<ref>{{cite journal|author=W. James|title=Are we automata?|journal=Mind|volume=4|issue=13|pages=1–22|year=1879|doi=10.1093/mind/os-4.13.1|author-link=William James|url=https://zenodo.org/record/1431809|access-date=2019-07-05|archive-date=2019-12-24|archive-url=https://web.archive.org/web/20191224150924/https://zenodo.org/record/1431809|url-status=live}}</ref><ref>{{cite journal|author=B.I.B. Lindahl|title=Consciousness and biological evolution|journal=Journal of Theoretical Biology|volume=187|issue=4|pages=613–629|year=1997|doi=10.1006/jtbi.1996.0394|pmid=9299304|bibcode=1997JThBi.187..613L}}</ref> [[Karl Popper]] develops a similar evolutionary argument in the book ''The Self and Its Brain''.<ref name=Popper1977>{{cite book|title=The Self and Its Brain|author=[[Karl Popper|Karl R. Popper]], [[John Eccles (neurophysiologist)|John C. Eccles]]|publisher=Springer International|year=1977|isbn=978-0-387-08307-0|url-access=registration|url=https://archive.org/details/selfitsbrain0000popp}}</ref>

Opinions are divided on when and how consciousness first arose. It has been argued that consciousness emerged (i) exclusively with the first humans, (ii) exclusively with the first mammals, (iii) independently in mammals and birds, or (iv) with the first reptiles.<ref>{{cite book|author=Peter Århem|author2=B.I.B. Lindahl|author3=Paul R. Manger|author4=Ann B. Butler|year=2008|editor=Hans Liljenström|editor2=Peter Århem|chapter=On the origin of consciousness—some amniote scenarios|title=Consciousness Transitions: Phylogenetic, Ontogenetic, and Physiological Aspects|publisher=Elsevier.|chapter-url=https://books.google.com/books?id=OQGJz1DVQNMC&pg=PA77|isbn=978-0-444-52977-0}}</ref> Other authors date the origins of consciousness to the first animals with nervous systems or early vertebrates in the Cambrian over 500 million years ago.<ref name="FeinbergMallat">{{cite journal|last1=Feinberg|first1=TE|last2=Mallatt|first2=J|date=October 2013|title=The evolutionary and genetic origins of consciousness in the Cambrian Period over 500 million years ago.|journal=Frontiers in Psychology|doi=10.3389/fpsyg.2013.00667|pmid=24109460|volume=4|pages=667|pmc=3790330|doi-access=free}}</ref> [[Donald Griffin]] suggests in his book ''Animal Minds'' a gradual evolution of consciousness.<ref name="Griffin2001"/> Further exploration of the origins of consciousness, particularly in molluscs, has been done by Peter Godfrey Smith in his book ''Metazoa''.<ref>{{Cite book |title=Metazoa |last=Godfrey Smith |first=Peter |year=2021 |isbn=9780008321239}}</ref>

Regarding the primary function of conscious processing, a recurring idea in recent theories is that phenomenal states somehow integrate neural activities and information-processing that would otherwise be independent.<ref>{{cite journal|author=Bernard Baars|title=The conscious access hypothesis: Origins and recent evidence|journal=Trends in Cognitive Sciences|volume=6|pages=47–52|pmid=11849615|doi=10.1016/S1364-6613(00)01819-2|issue=1|date=January 2002|s2cid=6386902|author-link=Bernard Baars}}</ref> This has been called the ''integration consensus''. Another example has been proposed by Gerald Edelman called dynamic core hypothesis which puts emphasis on [[reentry (neural circuitry)|reentrant]] connections that reciprocally link areas of the brain in a massively parallel manner.<ref>{{cite journal|last=Seth|first=Anil|author2=Eugene Izhikevich|author3=George Reeke|author4=Gerald Edelman|title=Theories and measures of consciousness: An extended framework|journal=Proceedings of the National Academy of Sciences|year=2006|volume=103|issue=28|doi=10.1073/pnas.0604347103|pages=10799–10804|pmid=16818879|pmc=1487169|bibcode=2006PNAS..10310799S|doi-access=free}}</ref> Edelman also stresses the importance of the evolutionary emergence of higher-order consciousness in humans from the historically older trait of primary consciousness which humans share with non-human animals (see ''[[#Neural correlates|Neural correlates]]'' section above). These theories of integrative function present solutions to two classic problems associated with consciousness: differentiation and unity. They show how our conscious experience can discriminate between a virtually unlimited number of different possible scenes and details (differentiation) because it integrates those details from our sensory systems, while the integrative nature of consciousness in this view easily explains how our experience can seem unified as one whole despite all of these individual parts. However, it remains unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. Nor is it explained what specific causal role conscious integration plays, nor why the same functionality cannot be achieved without consciousness. Not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyzes, etc.), and many kinds of information can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the [[ventriloquism effect]].<ref name="ReferenceA">{{cite journal|author=Ezequiel Morsella|year=2005|title=The function of phenomenal states: Supramodular Interaction Theory|journal=Psychological Review|volume=112|pages=1000–1021|pmid=16262477|issue=4|doi=10.1037/0033-295X.112.4.1000|s2cid=2298524|url=http://pdfs.semanticscholar.org/fdd7/81a15d0405a888abe4584a99ed9cbc6fb3ff.pdf|archive-url=https://web.archive.org/web/20201118022838/http://pdfs.semanticscholar.org/fdd7/81a15d0405a888abe4584a99ed9cbc6fb3ff.pdf|url-status=dead|archive-date=2020-11-18}}</ref> Hence it remains unclear why any of it is conscious. For a review of the differences between conscious and unconscious integrations, see the article of Ezequiel Morsella.<ref name="ReferenceA"/>

As noted earlier, even among writers who consider consciousness to be well-defined, there is [[Animal consciousness|widespread dispute]] about which animals other than humans can be said to possess it.<ref name = "ingvww">{{cite book|author=S. Budiansky|title=If a Lion Could Talk: Animal Intelligence and the Evolution of Consciousness|year=1998|publisher=The Free Press|isbn=978-0-684-83710-9|url=https://archive.org/details/iflioncouldtalka00budi}}</ref> Edelman has described this distinction as that of humans possessing higher-order consciousness while sharing the trait of primary consciousness with non-human animals (see previous paragraph). Thus, any examination of the evolution of consciousness is faced with great difficulties. Nevertheless, some writers have argued that consciousness can be viewed from the standpoint of [[evolutionary biology]] as an [[adaptation]] in the sense of a [[Phenotypic trait|trait]] that increases [[Fitness (biology)|fitness]].<ref>{{cite journal|author=S. Nichols|author2=T. Grantham|title=Adaptive Complexity and Phenomenal Consciousness|year=2000|journal=Philosophy of Science|volume=67|issue=4|pages=648–670|doi=10.1086/392859|url=http://dingo.sbs.arizona.edu/~snichols/Papers/evolcons(final).pdf|citeseerx=10.1.1.515.9722|s2cid=16484193|access-date=2017-10-25|archive-url=https://web.archive.org/web/20170813055023/http://dingo.sbs.arizona.edu/~snichols/Papers/evolcons(final).pdf|archive-date=2017-08-13|url-status=dead}}</ref> In his article "Evolution of consciousness", John Eccles argued that special anatomical and physical properties of the mammalian [[cerebral cortex]] gave rise to consciousness ("[a] psychon ... linked to [a] dendron through quantum physics").<ref>{{cite journal|author=John Eccles|title=Evolution of consciousness|journal=Proc. Natl. Acad. Sci. USA|volume=89|issue=16|pages=7320–7324|year=1992|pmid=1502142|pmc=49701|doi=10.1073/pnas.89.16.7320|bibcode=1992PNAS...89.7320E|author-link=John Eccles (neurophysiologist)|doi-access=free}}</ref> Bernard Baars proposed that once in place, this "recursive" circuitry may have provided a basis for the subsequent development of many of the functions that consciousness facilitates in higher organisms.<ref name=Baars>{{cite book|author=Bernard Baars|title=A Cognitive Theory of Consciousness|year=1993|publisher=Cambridge University Press|isbn=978-0-521-42743-2|author-link=Bernard Baars}}</ref> [[Peter Carruthers (philosopher)|Peter Carruthers]] has put forth one such potential adaptive advantage gained by conscious creatures by suggesting that consciousness allows an individual to make distinctions between appearance and reality.<ref>{{cite book|last=Carruthers|first=Peter|title=Phenomenal Consciousness: A Naturalistic Theory|year=2004|publisher=Cambridge University Press|location=Cambridge}}</ref> This ability would enable a creature to recognize the likelihood that their perceptions are deceiving them (e.g. that water in the distance may be a mirage) and behave accordingly, and it could also facilitate the manipulation of others by recognizing how things appear to them for both cooperative and devious ends.

Other philosophers, however, have suggested that consciousness would not be necessary for any functional advantage in evolutionary processes.<ref>{{cite journal|author=Owen Flanagan|author2=T.W. Polger|year=1995|title=Zombies and the function of consciousness|journal=Journal of Consciousness Studies|volume=2|pages=313–321|author-link=Owen Flanagan}}</ref><ref>{{cite journal|last=Rosenthal|first=David|title=Consciousness and its function|journal=Neuropsychologia|year=2008|volume=46|issue=3|pages=829–840|doi=10.1016/j.neuropsychologia.2007.11.012|pmid=18164042|s2cid=7791431}}</ref> No one has given a causal explanation, they argue, of why it would not be possible for a functionally equivalent non-conscious organism (i.e., a philosophical zombie) to achieve the very same survival advantages as a conscious organism. If evolutionary processes are blind to the difference between function ''F'' being performed by conscious organism ''O'' and non-conscious organism ''O*'', it is unclear what adaptive advantage consciousness could provide.<ref>{{cite book|author=Stevan Harnad|year=2002|chapter=Turing indistinguishability and the Blind Watchmaker|editor=J.H. Fetzer|title=Consciousness Evolving|publisher=John Benjamins|chapter-url=http://cogprints.org/1615|access-date=2011-10-26|author-link=Stevan Harnad|archive-date=2011-10-28|archive-url=https://web.archive.org/web/20111028162407/http://cogprints.org/1615/|url-status=live}}</ref> As a result, an exaptive explanation of consciousness has gained favor with some theorists that posit consciousness did not evolve as an adaptation but was an [[exaptation]] arising as a consequence of other developments such as increases in brain size or cortical rearrangement.<ref name="FeinbergMallat"/> Consciousness in this sense has been compared to the blind spot in the retina where it is not an adaption of the retina, but instead just a by-product of the way the retinal axons were wired.<ref>{{cite journal|author1=Zack Robinson|author2=Corey J. Maley|author3=Gualtiero Piccinini| year = 2015|title = Is Consciousness a Spandrel?.|journal = Journal of the American Philosophical Association|volume = 1|issue = 2| pages = 365–383|doi = 10.1017/apa.2014.10|s2cid=170892645}}</ref> Several scholars including [[Steven Pinker|Pinker]], [[Noam Chomsky|Chomsky]], [[Gerald Edelman|Edelman]], and [[Salvador Luria|Luria]] have indicated the importance of the emergence of human language as an important regulative mechanism of learning and memory in the context of the development of higher-order consciousness (see ''[[#Neural correlates|Neural correlates]]'' section above).

===Altered states===
{{Main|Altered state of consciousness}}
[[File:Abbot of Watkungtaphao in Phu Soidao Waterfall.jpg|thumb|upright|A Buddhist monk [[Meditation|meditating]]]]

There are some brain states in which consciousness seems to be absent, including dreamless sleep or coma. There are also a variety of circumstances that can change the relationship between the mind and the world in less drastic ways, producing what are known as altered states of consciousness. Some altered states occur naturally; others can be produced by drugs or brain damage.<ref name=Vaitl>{{cite journal|last=Vaitl|first=Dieter|s2cid=6909813|title=Psychobiology of altered states of consciousness|year=2005|journal=Psychological Bulletin|volume=131|pages=98–127|doi=10.1037/0033-2909.131.1.98|pmid=15631555|issue=1|url=https://pdfs.semanticscholar.org/09d8/95b85d772fb505144969310255c0cbdc74a7.pdf|archive-url=https://web.archive.org/web/20201022093127/https://pdfs.semanticscholar.org/09d8/95b85d772fb505144969310255c0cbdc74a7.pdf|url-status=dead|archive-date=2020-10-22}}</ref> Altered states can be accompanied by changes in thinking, disturbances in the sense of time, feelings of loss of control, changes in emotional expression, alternations in body image and changes in meaning or significance.<ref>{{cite book|last1=Schacter|first1=Daniel|last2=Gilbert|first2=Daniel|last3=Wegner|first3=Daniel|year=2011|title=Psychology 2nd Ed.|url=https://archive.org/details/psychology0000scha/page/190|location=New York|publisher=Worth Publishers|page=[https://archive.org/details/psychology0000scha/page/190 190]|isbn=978-1-4292-3719-2|access-date=27 October 2020}}</ref>

The two most widely accepted altered states are [[sleep]] and [[dream]]ing. Although dream sleep and non-dream sleep appear very similar to an outside observer, each is associated with a distinct pattern of brain activity, metabolic activity, and eye movement; each is also associated with a distinct pattern of experience and cognition. During ordinary non-dream sleep, people who are awakened report only vague and sketchy thoughts, and their experiences do not cohere into a continuous narrative. During dream sleep, in contrast, people who are awakened report rich and detailed experiences in which events form a continuous progression, which may however be interrupted by bizarre or fantastic intrusions.<ref>{{cite journal|last=Coenen|first=Anton|title=Subconscious Stimulus Recognition and Processing During Sleep|url=http://journalpsyche.org/files/0xbb10.pdf|year=2010|journal=Psyche: An Interdisciplinary Journal of Research on Consciousness|volume=16-2|url-status=live|archive-url=https://web.archive.org/web/20170611115233/http://journalpsyche.org/files/0xbb10.pdf|archive-date=2017-06-11}}</ref>{{Failed verification|date=August 2021|reason=This source talks about responses to auditory stimuli during sleep, but not about dreams or the difference between dream and non-dream sleep.}} Thought processes during the dream state frequently show a high level of irrationality. Both dream and non-dream states are associated with severe disruption of memory: it usually disappears in seconds during the non-dream state, and in minutes after awakening from a dream unless actively refreshed.<ref>{{cite book|last1= Hobson|first1=J. Allan|author-link1=Allan Hobson|last2=Pace-Schott|first2=Edward F.|last3=Stickgold|first3=Robert|author-link3=Robert Stickgold|year=2003|title=Sleep and Dreaming: Scientific Advances and Reconsiderations|editor1-last=Pace-Schott|editor1-first=Edward F.|editor2-last=Solms|editor2-first=Mark|editor3-last=Blagrove|editor3-first=Mark|editor4-last=Harnad|editor4-first=Stevan|publisher=Cambridge University Press|chapter=Dreaming and the brain: Toward a cognitive neuroscience of conscious states|isbn=978-0-521-00869-3|chapter-url=https://www.researchgate.net/publication/2599957|archive-url=https://web.archive.org/web/20210810234114/https://www.researchgate.net/profile/Edward-Pace-Schott/publication/2599957_Dreaming_and_the_Brain_Toward_a_Cognitive_Neuroscience_of_Conscious_States/links/02e7e52f240372e115000000/Dreaming-and-the-Brain-Toward-a-Cognitive-Neuroscience-of-Conscious-States.pdf|archive-date=2021-08-10|url-status=live}}</ref>

Research conducted on the effects of partial epileptic seizures on consciousness found that patients who have partial epileptic seizures experience altered states of consciousness.<ref>{{cite journal|author1=Johanson M.|author2=Valli K.|author3=Revonsuo A.|author4=Wedlund J.|year=2008|title=Content analysis of subjective experiences in partial epileptic seizures|journal=Epilepsy & Behavior|volume=12|issue=1|pages=170–182|doi=10.1016/j.yebeh.2007.10.002|pmid=18086461|s2cid =28276470}}</ref><ref>{{cite journal|author1=Johanson M.|author2=Valli K.|author3=Revonsuo A.|display-authors=etal|year=2008|title=Alterations in the contents of consciousness in partial epileptic seizures|journal=Epilepsy & Behavior|volume=13|issue=2| pages=366–371|doi=10.1016/j.yebeh.2008.04.014|pmid=18522873|s2cid=24473529}}</ref> In partial epileptic seizures, consciousness is impaired or lost while some aspects of consciousness, often automated behaviors, remain intact. Studies found that when measuring the qualitative features during partial epileptic seizures, patients exhibited an increase in arousal and became absorbed in the experience of the seizure, followed by difficulty in focusing and shifting attention.

A variety of [[psychoactive drug]]s, including [[Ethanol|alcohol]], have notable effects on consciousness.<ref name="DSMIV">{{Cite book|date=31 July 1994|title=Diagnostic and statistical manual of mental disorders: DSM-IV|url=https://books.google.com/books?id=W-BGAAAAMAAJ|edition=DSM-IV-TR|location=Washington, DC|publisher=American Psychiatric Association|isbn=978-0-89042-025-6}}</ref> These range from a simple dulling of awareness produced by [[sedative]]s, to increases in the intensity of sensory qualities produced by [[stimulant]]s, [[cannabis (drug)|cannabis]], [[empathogen-entactogen|empathogens–entactogens]] such as [[MDMA]] ("Ecstasy"), or most notably by the class of drugs known as [[psychedelic drug|psychedelics]].<ref name=Vaitl/> [[Lysergic acid diethylamide|LSD]], [[mescaline]], [[psilocybin]], [[N,N-Dimethyltryptamine|dimethyltryptamine]], and others in this group can produce major distortions of perception, including hallucinations; some users even describe their drug-induced experiences as mystical or spiritual in quality. The brain mechanisms underlying these effects are not as well understood as those induced by use of alcohol,<ref name="DSMIV"/> but there is substantial evidence that alterations in the brain system that uses the chemical neurotransmitter [[serotonin]] play an essential role.<ref>{{cite web|url=http://epublications.bond.edu.au/hss_pubs/10|title=The neurochemistry of psychedelic experiences|last=Lyvers|first=Michael|year=2003|publisher=ePublications@bond|format=PDF|access-date=2011-10-26|archive-date=2012-04-20|archive-url=https://web.archive.org/web/20120420042607/http://epublications.bond.edu.au/hss_pubs/10/|url-status=live}}</ref>

There has been some research into physiological changes in yogis and people who practise various techniques of [[meditation]]. Some research with brain waves during meditation has reported differences between those corresponding to ordinary relaxation and those corresponding to meditation. It has been disputed, however, whether there is enough evidence to count these as physiologically distinct states of consciousness.<ref name=MurphyMeditation>{{cite book|author1=M. Murphy|author2=S. Donovan|author3=E. Taylor|year=1997|title=The Physical and Psychological Effects of Meditation: A Review of Contemporary Research With a Comprehensive Bibliography, 1931–1996|publisher=Institute of Noetic Sciences}}</ref>

The most extensive study of the characteristics of altered states of consciousness was made by psychologist [[Charles Tart]] in the 1960s and 1970s. Tart analyzed a state of consciousness as made up of a number of component processes, including exteroception (sensing the external world); [[interoception]] (sensing the body); input-processing (seeing meaning); emotions; memory; time sense; sense of identity; evaluation and cognitive processing; motor output; and interaction with the environment.<ref>{{cite book|last=Tart|first=Charles|author-link=Charles Tart|year=2001|title=States of Consciousness|publisher=IUniverse.com|chapter=Ch. 2: The components of consciousness|chapter-url=http://www.psychedelic-library.org/soc2.htm|isbn=978-0-595-15196-7|access-date=5 October 2011|archive-date=6 November 2011|archive-url=https://web.archive.org/web/20111106032020/http://www.psychedelic-library.org/soc2.htm|url-status=live}}</ref>{{self-published source|date=January 2023}} Each of these, in his view, could be altered in multiple ways by drugs or other manipulations. The components that Tart identified have not, however, been validated by empirical studies. Research in this area has not yet reached firm conclusions, but a recent questionnaire-based study identified eleven significant factors contributing to drug-induced states of consciousness: experience of unity; spiritual experience; blissful state; insightfulness; disembodiment; impaired control and cognition; anxiety; complex imagery; elementary imagery; audio-visual [[synesthesia]]; and changed meaning of percepts.<ref>{{cite journal|last1=Studerus|first1=Erich|last2=Gamma|first2=Alex|last3=Vollenweider|first3=Franz X.|year=2010|editor-last=Bell|editor-first=Vaughan|title=Psychometric evaluation of the altered states of consciousness rating scale (OAV)|journal=[[PLOS One]]|volume=5|issue=8|pages=e12412|bibcode=2010PLoSO...512412S|doi=10.1371/journal.pone.0012412|pmc=2930851|pmid=20824211|doi-access=free}}</ref>