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Theories of consciousness

Abstract

Recent years have seen a blossoming of theories about the biological and physical basis of consciousness. Good theories guide empirical research, allowing us to interpret data, develop new experimental techniques and expand our capacity to manipulate the phenomenon of interest. Indeed, it is only when couched in terms of a theory that empirical discoveries can ultimately deliver a satisfying understanding of a phenomenon. However, in the case of consciousness, it is unclear how current theories relate to each other, or whether they can be empirically distinguished. To clarify this complicated landscape, we review four prominent theoretical approaches to consciousness: higher-order theories, global workspace theories, re-entry and predictive processing theories and integrated information theory. We describe the key characteristics of each approach by identifying which aspects of consciousness they propose to explain, what their neurobiological commitments are and what empirical data are adduced in their support. We consider how some prominent empirical debates might distinguish among these theories, and we outline three ways in which theories need to be developed to deliver a mature regimen of theory-testing in the neuroscience of consciousness. There are good reasons to think that the iterative development, testing and comparison of theories of consciousness will lead to a deeper understanding of this most profound of mysteries.

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Fig. 1: Higher-order theories.
Fig. 2: Global workspace theories.
Fig. 3: Integrated information theory.
Fig. 4: Re-entry theory and predictive processing.

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References

  1. Crick, F. & Koch, C. Towards a neurobiological theory of consciousness. Semin. Neurosci. 2, 263–275 (1990).

    Google Scholar 

  2. Metzinger, T. (ed.) Neural Correlates of Consciousness: Empirical and Conceptual Questions (MIT Press, 2000).

  3. Koch, C., Massimini, M., Boly, M. & Tononi, G. Neural correlates of consciousness: progress and problems. Nat. Rev. Neurosci. 17, 307–321 (2016).

    Article  CAS  PubMed  Google Scholar 

  4. de Graaf, T. A., Hsieh, P. J. & Sack, A. T. The ‘correlates’ in neural correlates of consciousness. Neurosci. Biobehav. Rev. 36, 191–197 (2012).

    Article  PubMed  Google Scholar 

  5. Aru, J., Bachmann, T., Singer, W. & Melloni, L. Distilling the neural correlates of consciousness. Neurosci. Biobehav. Rev. 36, 737–746 (2012).

    Article  PubMed  Google Scholar 

  6. Tsuchiya, N., Wilke, M., Frassle, S. & Lamme, V. A. No-report paradigms: extracting the true neural correlates of consciousness. Trends Cogn. Sci. 19, 757–770 (2015).

    Article  PubMed  Google Scholar 

  7. Klein, C., Hohwy, J. & Bayne, T. Explanation in the science of consciousness: from the neural correlates of consciousness (NCCs) to the difference-makers of consciousness (DMCs). Philos. Mind Sci. https://doi.org/10.33735/phimisci.2020.II.60 (2020).

    Article  Google Scholar 

  8. Michel, M. et al. Opportunities and challenges for a maturing science of consciousness. Nat. Hum. Behav. 3, 104–107 (2019).

    Article  PubMed  PubMed Central  Google Scholar 

  9. Seth, A. K. Consciousness: the last 50 years (and the next). Brain Neurosci. Adv. 2, 2398212818816019 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  10. Seth, A. K. Explanatory correlates of consciousness: theoretical and computational challenges. Cogn. Comput. 1, 50–63 (2009).

    Article  Google Scholar 

  11. Searle, J. The Rediscovery of the Mind (MIT Press, 1992).

  12. Varela, F. J. Neurophenomenology: a methodological remedy for the hard problem. J. Conscious. Stud. 3, 330–350 (1996).

    Google Scholar 

  13. Seth, A. K. Being You: A New Science of Consciousness (Faber & Faber, 2021).

  14. Dennett, D. C. Welcome to strong illusionism. J. Conscious. Stud. 26, 48–58 (2019).

    Google Scholar 

  15. Frankish, K. Illusionism as a Theory of Consciousness (Imprint Academic, 2017).

  16. Wiese, W. The science of consciousness does not need another theory, it needs a minimal unifying model. Neurosci. Conscious. 2020, niaa013 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  17. Melloni, L., Mudrik, L., Pitts, M. & Koch, C. Making the hard problem of consciousness easier. Science 372, 911–912 (2021). This work sets out how an adversarial collaboration is planning to arbitrate between integrated information and global workspace ToCs.

    Article  CAS  PubMed  Google Scholar 

  18. Hameroff, S. & Penrose, R. Consciousness in the universe: a review of the ‘Orch OR’ theory. Phys. Life Rev. 11, 39–78 (2014).

    Article  PubMed  Google Scholar 

  19. Chalmers, D. J. & McQueen, K. in Quantum Mechanics and Consciousness (ed Gao, S.) (Oxford Univ. Press, 2022).

  20. Nagel, T. What is it like to be a bat? Philos. Rev. 83, 435–450 (1974).

    Article  Google Scholar 

  21. Bayne, T., Hohwy, J. & Owen, A. M. Are there levels of consciousness? Trends Cogn. Sci. 20, 405–413 (2016). This work challenges the common unidimensional notion of ‘level of consciousness’, outlining an alternative, richer, multidimensional account.

    Article  PubMed  Google Scholar 

  22. Metzinger, T. Being No-One (MIT Press, 2003).

  23. Damasio, A. Self Comes To Mind: Constructing the Conscious Brain (William Heinemann, 2010).

  24. Park, H. D. & Tallon-Baudry, C. The neural subjective frame: from bodily signals to perceptual consciousness. Philos. Trans. R. Soc. Lond. B Biol. Sci. 369, 20130208 (2014).

    Article  PubMed  PubMed Central  Google Scholar 

  25. Bayne, T. The Unity of Consciousness (Oxford Univ. Press, 2010).

  26. Bayne, T. & Chalmers, D. J. in The Unity of Consciousness: Binding, Integration, and Dissociation (ed Cleeremans, A.) 23–58 (Oxford Univ. Press, 2003).

  27. Cummins, R. Functional analysis. J. Philos. 72, 741–765 (1975).

    Article  Google Scholar 

  28. Blake, R., Brascamp, J. & Heeger, D. J. Can binocular rivalry reveal neural correlates of consciousness? Philos. Trans. R. Soc. Lond. B Biol. Sci. 369, 20130211 (2014).

    Article  PubMed  PubMed Central  Google Scholar 

  29. Signorelli, C. M., Szczotka, J. & Prentner, R. Explanatory profiles of models of consciousness — towards a systematic classification. Neurosci. Conscious. 2021, niab021 (2021).

    Article  PubMed  PubMed Central  Google Scholar 

  30. Lau, H. & Rosenthal, D. Empirical support for higher-order theories of conscious awareness. Trends Cogn. Sci. 15, 365–373 (2011). This work presents a summary of empirical evidence favouring higher-order ToCs.

    Article  PubMed  Google Scholar 

  31. Rosenthal, D. Consciousness and Mind (Clarendon, 2005).

  32. Brown, R. The HOROR theory of phenomenal consciousness. Philos. Stud. 172, 1783–1794 (2015).

    Article  Google Scholar 

  33. Cleeremans, A. Consciousness: the radical plasticity thesis. Prog. Brain Res. 168, 19–33 (2008).

    Article  PubMed  Google Scholar 

  34. Cleeremans, A. et al. Learning to be conscious. Trends Cogn. Sci. 24, 112–123 (2020).

    Article  PubMed  Google Scholar 

  35. Fleming, S. M. Awareness as inference in a higher-order state space. Neurosci. Conscious. 2020, niz020 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  36. Lau, H. Consciousness, metacognition, and perceptual reality monitoring. Preprint at ArXiv https://doi.org/10.31234/osf.io/ckbyf (2020).

    Article  Google Scholar 

  37. Gershman, S. J. The generative adversarial brain. Front. Artif. Intell. https://doi.org/10.3389/frai.2019.00018 (2019).

    Article  PubMed  PubMed Central  Google Scholar 

  38. Cohen, M. A., Dennett, D. C. & Kanwisher, N. What is the bandwidth of perceptual experience? Trends Cogn. Sci. 20, 324–335 (2016).

    Article  PubMed  PubMed Central  Google Scholar 

  39. Haun, A. M., Tononi, G., Koch, C. & Tsuchiya, N. Are we underestimating the richness of visual experiences? Neurosci. Conscious. 3, 1–4 (2017).

    Google Scholar 

  40. Odegaard, B., Chang, M. Y., Lau, H. & Cheung, S. H. Inflation versus filling-in: why we feel we see more than we actually do in peripheral vision. Philos. Trans. R. Soc. Lond. B Biol. Sci. https://doi.org/10.1098/rstb.2017.0345 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  41. LeDoux, J. E. & Brown, R. A higher-order theory of emotional consciousness. Proc. Natl Acad. Sci. USA 114, E2016–E2025 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  42. Morrison, J. Perceptual confidence. Anal. Philos. 78, 99–147 (2016).

    Google Scholar 

  43. Peters, M. A. K. Towards characterizing the canonical computations generating phenomenal experience. Preprint at PsyArXiv https://doi.org/10.31234/osf.io/bqfr6 (2021).

    Article  Google Scholar 

  44. Rosenthal, D. Consciousness and its function. Neuropsychologia 46, 829–840 (2008).

    Article  PubMed  Google Scholar 

  45. Charles, L., Van Opstal, F., Marti, S. & Dehaene, S. Distinct brain mechanisms for conscious versus subliminal error detection. Neuroimage 73, 80–94 (2013).

    Article  PubMed  Google Scholar 

  46. Brown, R., Lau, H. & LeDoux, J. E. Understanding the higher-order approach to consciousness. Trends Cogn. Sci. 23, 754–768 (2019).

    Article  PubMed  Google Scholar 

  47. Baars, B. J. A Cognitive Theory of Consciousness (Cambridge Univ. Press, 1988).

  48. Dehaene, S. & Changeux, J. P. Experimental and theoretical approaches to conscious processing. Neuron 70, 200–227 (2011).

    Article  CAS  PubMed  Google Scholar 

  49. Mashour, G. A., Roelfsema, P., Changeux, J. P. & Dehaene, S. Conscious processing and the global neuronal workspace hypothesis. Neuron 105, 776–798 (2020). This work presents a summary of the neuronal GWT and its supporting evidence.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  50. Dehaene, S., Sergent, C. & Changeux, J. P. A neuronal network model linking subjective reports and objective physiological data during conscious perception. Proc. Natl Acad. Sci. USA 100, 8520–8525 (2003).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  51. Naccache, L. Why and how access consciousness can account for phenomenal consciousness. Philos. Trans. R. Soc. Lond. B Biol. Sci. https://doi.org/10.1098/rstb.2017.0357 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  52. Mashour, G. A. Cognitive unbinding: a neuroscientific paradigm of general anesthesia and related states of unconsciousness. Neurosci. Biobehav. Rev. 37, 2751–2759 (2013).

    Article  PubMed  Google Scholar 

  53. Demertzi, A. et al. Human consciousness is supported by dynamic complex patterns of brain signal coordination. Sci. Adv. 5, eaat7603 (2019). This large empirical study of functional connectivity patterns across different global states of consciousness focuses on how these patterns relate to underlying structural connectivity.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  54. Barttfeld, P. et al. Signature of consciousness in the dynamics of resting-state brain activity. Proc. Natl Acad. Sci. USA 112, 887–892 (2015).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  55. Uhrig, L. et al. Resting-state dynamics as a cortical signature of anesthesia in monkeys. Anesthesiology 129, 942–958 (2018).

    Article  PubMed  Google Scholar 

  56. Carruthers, P. Human and Animal Minds: The Consciousness Questions Laid to Rest (Oxford Univ. Press, 2019).

  57. Tononi, G. Consciousness as integrated information: a provisional manifesto. Biol. Bull. 215, 216–242 (2008).

    Article  PubMed  Google Scholar 

  58. Tononi, G. Integrated information theory of consciousness: an updated account. Arch. Ital. Biol. 150, 293–329 (2012).

    CAS  PubMed  Google Scholar 

  59. Tononi, G., Boly, M., Massimini, M. & Koch, C. Integrated information theory: from consciousness to its physical substrate. Nat. Rev. Neurosci. 17, 450–461 (2016). This work presents an account of the core claims and concepts of the integrated information ToC.

    Article  CAS  PubMed  Google Scholar 

  60. Oizumi, M., Albantakis, L. & Tononi, G. From the phenomenology to the mechanisms of consciousness: integrated information theory 3.0. PLoS Comput. Biol. 10, e1003588 (2014).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  61. Tononi, G. & Koch, C. Consciousness: here, there and everywhere? Philos. Trans. R. Soc. Lond. B Biol. Sci. https://doi.org/10.1098/rstb.2014.0167 (2015).

    Article  PubMed  PubMed Central  Google Scholar 

  62. Haun, A. M. & Tononi, G. Why does space feel the way it does? Towards a principled account of spatial experienc. Entropy 21, 1160 (2019).

    Article  PubMed Central  Google Scholar 

  63. Albantakis, L., Hintze, A., Koch, C., Adami, C. & Tononi, G. Evolution of integrated causal structures in animats exposed to environments of increasing complexity. PLoS Comput. Biol. 10, e1003966 (2014).

    Article  PubMed  PubMed Central  Google Scholar 

  64. Marshall, W., Gomez-Ramirez, J. & Tononi, G. Integrated information and state differentiation. Front. Psychol. 7, 926 (2016).

    Article  PubMed  PubMed Central  Google Scholar 

  65. Lamme, V. A. Towards a true neural stance on consciousness. Trends Cogn. Sci. 10, 494–501 (2006).

    Article  PubMed  Google Scholar 

  66. Lamme, V. A. & Roelfsema, P. R. The distinct modes of vision offered by feedforward and recurrent processing. Trends Neurosci. 23, 571–579 (2000).

    Article  CAS  PubMed  Google Scholar 

  67. Hohwy, J. & Seth, A. K. Predictive processing as a systematic basis for identifying the neural correlates of consciousness. Philos. Mind Sci. 1, 3 (2020).

    Google Scholar 

  68. Lamme, V. A., Super, H., Landman, R., Roelfsema, P. R. & Spekreijse, H. The role of primary visual cortex (V1) in visual awareness. Vis. Res. 40, 1507–1521 (2000).

    Article  CAS  PubMed  Google Scholar 

  69. Pascual-Leone, A. & Walsh, V. Fast backprojections from the motion to the primary visual area necessary for visual awareness. Science 292, 510–512 (2001). This early study uses transcranial magnetic stimulation to reveal a role for re-entrant activity in conscious visual perception in humans.

    Article  CAS  PubMed  Google Scholar 

  70. Boehler, C. N., Schoenfeld, M. A., Heinze, H. J. & Hopf, J. M. Rapid recurrent processing gates awareness in primary visual cortex. Proc. Natl Acad. Sci. USA 105, 8742–8747 (2008).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  71. Lamme, V. A. How neuroscience will change our view on consciousness. Cogn. Neurosci. 1, 204–220 (2010).

    Article  PubMed  Google Scholar 

  72. von Helmholtz, H. Handbuch der Phsyiologischen Optik [German] (Voss, 1867).

  73. Clark, A. Whatever next? Predictive brains, situated agents, and the future of cognitive science. Behav. Brain Sci. 36, 181–204 (2013). This work presents a classic exposition of predictive processing and its relevance for perception, cognition and action.

    Article  PubMed  Google Scholar 

  74. Friston, K. J. The free-energy principle: a unified brain theory? Nat. Rev. Neurosci. 11, 127–138 (2010).

    Article  CAS  PubMed  Google Scholar 

  75. Seth, A. K. in Open MIND (eds Windt, J. M. & Metzinger, T.) (MIND Group, 2015).

  76. Friston, K. J. Am I self-conscious? (Or does self-organization entail self-consciousness?). Front. Psychol. 9, 579 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  77. Seth, A. K. & Tsakiris, M. Being a beast machine: the somatic basis of selfhood. Trends Cogn. Sci. 22, 969–981 (2018).

    Article  PubMed  Google Scholar 

  78. Bruineberg, J., Dolega, K., Dewhurst, J. & Baltieri, M. The Emperor’s new Markov blankets. Behav. Brain Sci. https://doi.org/10.1017/S0140525X21002351 (2021).

    Article  PubMed  Google Scholar 

  79. Hohwy, J. The Predictive Mind (Oxford Univ. Press, 2013).

  80. Rao, R. P. & Ballard, D. H. Predictive coding in the visual cortex: a functional interpretation of some extra-classical receptive-field effects. Nat. Neurosci. 2, 79–87 (1999).

    Article  CAS  PubMed  Google Scholar 

  81. Teufel, C. & Fletcher, P. C. Forms of prediction in the nervous system. Nat. Rev. Neurosci. 21, 231–242 (2020).

    Article  CAS  PubMed  Google Scholar 

  82. Friston, K. J., Daunizeau, J., Kilner, J. & Kiebel, S. J. Action and behavior: a free-energy formulation. Biol. Cybern. 102, 227–260 (2010).

    Article  PubMed  Google Scholar 

  83. Parr, T. & Friston, K. J. Generalised free energy and active inference. Biol. Cybern. 113, 495–513 (2019).

    Article  PubMed  PubMed Central  Google Scholar 

  84. Pennartz, C. M. A. Consciousness, representation, action: the importance of being goal-directed. Trends Cogn. Sci. 22, 137–153 (2018).

    Article  PubMed  Google Scholar 

  85. Williford, K., Bennequin, D., Friston, K. & Rudrauf, D. The projective consciousness model and phenomenal selfhood. Front. Psychol. 9, 2571 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  86. Hohwy, J. New directions in predictive processing. Mind Lang. 35, 209–223 (2020).

    Article  Google Scholar 

  87. Seth, A. K. A predictive processing theory of sensorimotor contingencies: explaining the puzzle of perceptual presence and its absence in synesthesia. Cogn. Neurosci. 5, 97–118 (2014).

    Article  PubMed  PubMed Central  Google Scholar 

  88. O’Regan, J. K. & Noë, A. A sensorimotor account of vision and visual consciousness. Behav. Brain Sci. 24, 939–973; discussion 973–1031 (2001). This primary description of the sensorimotor ToC argues that conscious perception is intimately related to action.

    Article  PubMed  Google Scholar 

  89. Seth, A. K. Interoceptive inference, emotion, and the embodied self. Trends Cogn. Sci. 17, 565–573 (2013). This work presents a theoretical application of predictive processing to interoception and physiological regulation, relating this to experiences of emotion and selfhood.

    Article  PubMed  Google Scholar 

  90. Barrett, L. F. The theory of constructed emotion: an active inference account of interoception and categorization. Soc. Cogn. Affect. Neurosci. 12, 1833 (2017).

    Article  PubMed  PubMed Central  Google Scholar 

  91. Solms, M. The hard problem of consciousness and the free energy principle. Front. Psychol. 9, 2714 (2018).

    Article  PubMed  Google Scholar 

  92. Hohwy, J., Roepstorff, A. & Friston, K. Predictive coding explains binocular rivalry: an epistemological review. Cognition 108, 687–701 (2008).

    Article  PubMed  Google Scholar 

  93. Parr, T., Corcoran, A. W., Friston, K. J. & Hohwy, J. Perceptual awareness and active inference. Neurosci. Conscious. 2019, niz012 (2019).

    Article  PubMed  PubMed Central  Google Scholar 

  94. Friston, K. J., FitzGerald, T., Rigoli, F., Schwartenbeck, P. & Pezzulo, G. Active inference: a process theory. Neural Comput. 29, 1–49 (2017).

    Article  PubMed  Google Scholar 

  95. Boly, M. et al. Preserved feedforward but impaired top-down processes in the vegetative state. Science 332, 858–862 (2011). This neuroimaging study uses dynamic causal modelling to show that loss of consciousness in the vegetative state is associated with impaired top-down connectivity from frontal to temporal cortices.

    Article  CAS  PubMed  Google Scholar 

  96. Parr, T. & Friston, K. J. Working memory, attention, and salience in active inference. Sci. Rep. 7, 14678 (2017).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  97. Chalmers, A. What is This Thing Called Science? (Queensland Univ. Press, 2013).

  98. Godfrey-Smith, P. G. Theory and Reality: An Introduction to the Philosophy of Science 2nd edn (Univ. Chicago Press, 2021).

  99. Lipton, P. Inference to the Best Explanation (Routledge, 2004).

  100. Lau, H. & Passingham, R. E. Relative blindsight in normal observers and the neural correlate of visual consciousness. Proc. Natl Acad. Sci. USA 103, 18763–18768 (2006). This empirical study compares conscious and unconscious visual perception in humans, controlling for performance, and reveals differences in prefrontal activation.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  101. van Vugt, B. et al. The threshold for conscious report: signal loss and response bias in visual and frontal cortex. Science 360, 537–542 (2018). This empirical study tracks the time course of neural signals in primate frontal cortex, showing that perceived stimuli elicit sustained activity, when compared with non-perceived stimuli.

    Article  PubMed  CAS  Google Scholar 

  102. Gaillard, R. et al. Converging intracranial markers of conscious access. PLoS Biol. 7, e61 (2009).

    Article  PubMed  CAS  Google Scholar 

  103. Panagiotaropoulos, T. I., Deco, G., Kapoor, V. & Logothetis, N. K. Neuronal discharges and gamma oscillations explicitly reflect visual consciousness in the lateral prefrontal cortex. Neuron 74, 924–935 (2012).

    Article  CAS  PubMed  Google Scholar 

  104. Kapoor, V. et al. Decoding internally generated transitions of conscious contents in the prefrontal cortex without subjective reports. Nat. Comm. 13, 1535 (2022).

    Article  CAS  Google Scholar 

  105. Bellet, J. et al. Decoding rapidly presented visual stimuli from prefrontal ensembles without report nor post-perceptual processing. Neurosci. Conscious. 2022, niac005 (2022).

    Article  PubMed  PubMed Central  Google Scholar 

  106. Levinson, M., Podvalny, E., Baete, S. H. & He, B. J. Cortical and subcortical signatures of conscious object recognition. Nat. Commun. 12, 2930 (2021).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  107. Boly, M. et al. Are the neural correlates of consciousness in the front or in the back of the cerebral cortex? Clinical and neuroimaging evidence. J. Neurosci. 37, 9603–9613 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  108. Raccah, O., Block, N. & Fox, K. C. R. Does the prefrontal cortex play an essential role in consciousness? Insights from intracranial electrical stimulation of the human brain. J. Neurosci. 41, 2076–2087 (2021).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  109. Odegaard, B., Knight, R. T. & Lau, H. Should a few null findings falsify prefrontal theories of conscious perception? J. Neurosci. 37, 9593–9602 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  110. Brascamp, J., Blake, R. & Knapen, T. Negligible fronto-parietal BOLD activity accompanying unreportable switches in bistable perception. Nat. Neurosci. 18, 1672–1678 (2015). This empirical ‘no-report’ study shows that fronto-parietal activity does not track switches in perceptual dominance when subjective reports are not required.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  111. Sergent, C. et al. Bifurcation in brain dynamics reveals a signature of conscious processing independent of report. Nat. Commun. 12, 1149 (2021).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  112. Siclari, F. et al. The neural correlates of dreaming. Nat. Neurosci. 20, 872–878 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  113. Wong, W. et al. The Dream Catcher experiment: blinded analyses failed to detect markers of dreaming consciousness in EEG spectral power. Neurosci. Conscious. 2020, niaa006 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  114. Block, N. Consciousness, accessibility, and the mesh between psychology and neuroscience. Behav. Brain Sci. 30, 481–548 (2007). This work argues that research in psychology and neuroscience shows that there is a real and not merely conceptual distinction between phenomenal consciousness (that is, experience) and cognitive access to phenomenal consciousness.

    Article  PubMed  Google Scholar 

  115. Musgrave, A. in Relativism and Realism in Science (ed Nola, R.) 229–252 (Kluwer, 1988).

  116. Song, C., Haun, A. M. & Tononi, G. Plasticity in the structure of visual space. eNeuro https://doi.org/10.1523/ENEURO.0080-17.2017 (2017).

    Article  PubMed  PubMed Central  Google Scholar 

  117. Marshel, J. H. et al. Cortical layer-specific critical dynamics triggering perception. Science https://doi.org/10.1126/science.aaw5202 (2019).

    Article  PubMed  PubMed Central  Google Scholar 

  118. Dembski, C., Koch, C. & Pitts, M. Perceptual awareness negativity: a physiological correlate of sensory consciousness. Trends Cogn. Sci. 25, 660–670 (2021).

    Article  PubMed  Google Scholar 

  119. Sanchez, G., Hartmann, T., Fusca, M., Demarchi, G. & Weisz, N. Decoding across sensory modalities reveals common supramodal signatures of conscious perception. Proc. Natl Acad. Sci. USA 117, 7437–7446 (2020).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  120. Sergent, C. The offline stream of conscious representations. Philos. Trans. R. Soc. Lond. B Biol. Sci. https://doi.org/10.1098/rstb.2017.0349 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  121. Michel, M. & Doerig, A. A new empirical challenge for local theories of consciousness. Mind Lang. https://doi.org/10.1111/mila.12319 (2021).

    Article  Google Scholar 

  122. Sergent, C. et al. Cueing attention after the stimulus is gone can retrospectively trigger conscious perception. Curr. Biol. 23, 150–155 (2013). This empirical study reveals that conscious perception of a stimulus can be influenced by events happening (hundreds of milliseconds) after the stimulus appeared (‘retro-perception’).

    Article  CAS  PubMed  Google Scholar 

  123. Roseboom, W. et al. Activity in perceptual classification networks as a basis for human subjective time perception. Nat. Commun. 10, 267 (2019).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  124. Kent, L. & Wittmann, M. Special Issue: Consciousness science and its theories. Time consciousness: the missing link in theories of consciousness. Neurosci. Conscious. 2021, niab011 (2021).

    Article  PubMed  PubMed Central  Google Scholar 

  125. Husserl, E. Ideas: A General Introduction to Pure Phenomenology (Collier Books, 1963).

  126. Yaron, I., Melloni, L., Pitts, M. & Mudrik, L. The ConTraSt database for analyzing and comparing empirical studies of consciousness theories. Nat. Hum. Behav. https://doi.org/10.1038/s41562-021-01284-5 (2022). This work presents an online resource of empirical studies of consciousness, organized with respect to different ToCs.

    Article  PubMed  Google Scholar 

  127. Joglekar, M. R., Mejias, J. F., Yang, G. R. & Wang, X. J. Inter-areal balanced amplification enhances signal propagation in a large-scale circuit model of the primate cortex. Neuron 98, 222–234.e8 (2018).

    Article  CAS  PubMed  Google Scholar 

  128. VanRullen, R. & Kanai, R. Deep learning and the global workspace theory. Trends Neurosci. 44, 692–704 (2021).

    Article  CAS  PubMed  Google Scholar 

  129. Shea, N. & Frith, C. D. The global workspace needs metacognition. Trends Cogn. Sci. 23, 560–571 (2019).

    Article  PubMed  Google Scholar 

  130. Suzuki, K., Roseboom, W., Schwartzman, D. J. & Seth, A. K. A deep-dream virtual reality platform for studying altered perceptual phenomenology. Sci. Rep. 7, 15982 (2017).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  131. Vilas, M. G., Auksztulewicz, R. & Melloni, L. Active inference as a computational framework for consciousness. Rev. Philos. Psychol. https://doi.org/10.1007/s13164-021-00579-w (2021).

    Article  Google Scholar 

  132. Browning, H. & Veit, W. The measurement problem in consciousness. Philos. Top. 48, 85–108 (2020).

    Article  Google Scholar 

  133. Seth, A. K., Dienes, Z., Cleeremans, A., Overgaard, M. & Pessoa, L. Measuring consciousness: relating behavioural and neurophysiological approaches. Trends Cogn. Sci. 12, 314–321 (2008).

    Article  PubMed  PubMed Central  Google Scholar 

  134. Michel, M. Calibration in consciousness science. Erkenntnis https://doi.org/10.1007/s10670-021-00383-z (2021).

    Article  Google Scholar 

  135. Birch, J., Schnell, A. K. & Clayton, N. S. Dimensions of animal consciousness. Trends Cogn. Sci. 24, 789–801 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  136. Bayne, T., Seth, A. K. & Massimini, M. Are there islands of awareness? Trends Neurosci. 43, 6–16 (2020). This work presents an examination of the possibility of consciousness in isolated neural systems such as brain organoids, disconnected cortical hemispheres and ex cranio brains.

    Article  CAS  PubMed  Google Scholar 

  137. Dehaene, S., Lau, H. & Kouider, S. What is consciousness, and could machines have it? Science 358, 486–492 (2017).

    Article  CAS  PubMed  Google Scholar 

  138. Hu, H., Cusack, R. & Naci, L. Typical and disrupted brain circuitry for conscious awareness in full-term and pre-term infants. (2021).

  139. Owen, A. M. & Coleman, M. R. Detecting awareness in the vegetative state. Ann. N Y Acad. Sci. 9, 130–138 (2008).

    Article  Google Scholar 

  140. Cleeremans, A. The radical plasticity thesis: how the brain learns to be conscious. Front. Psychol. 2, 86 (2011).

    Article  PubMed  PubMed Central  Google Scholar 

  141. Jackendoff, R. Consciousness and the Computational Mind (MIT Press, 1987).

  142. Prinz, J. The Conscious Brain: How Attention Engenders Experience (Oxford Univ. Press, 2012).

  143. Chang, A. Y. C., Biehl, M., Yu, Y. & Kanai, R. Information closure theory of consciousness. Front. Psychol. 11, 1504 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  144. Tononi, G. & Edelman, G. M. Consciousness and complexity. Science 282, 1846–1851 (1998). This work presents an early proposal of how measures of neural complexity might relate to phenomenological properties of (all) conscious experiences.

    Article  CAS  PubMed  Google Scholar 

  145. Edelman, G. M. Neural Darwinism: The Theory of Neuronal Group Selection (Basic Books 1987).

  146. Edelman, G. M. The Remembered Present (Basic Books, 1989).

  147. Damasio, A. The Feeling of What Happens: Body and Emotion in the Making of Consciousness (Harvest Books, 2000).

  148. Graziano, M. S. A. The attention schema theory: a foundation for engineering artificial consciousness. Front. Robot. AI 4, 60 (2017).

    Article  Google Scholar 

  149. Dennett, D. C. Consciousness Explained (Little, Brown, 1991).

  150. Ginsburg, S. & Jablonka, E. The Evolution of the Sensitive Soul: Learning and the Origins of Consciousness (MIT Press, 2019).

  151. Aru, J., Suzuki, M. & Larkum, M. E. Cellular mechanisms of conscious processing. Trends Cogn. Sci. 24, 814–825 (2020).

    Article  PubMed  Google Scholar 

  152. McFadden, J. Integrating information in the brain’s EM field: the cemi field theory of consciousness. Neurosci. Conscious. 2020, niaa016 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  153. Fleming, S. M., Ryu, J., Golfinos, J. G. & Blackmon, K. E. Domain-specific impairment in metacognitive accuracy following anterior prefrontal lesions. Brain 137, 2811–2822 (2014).

    Article  PubMed  PubMed Central  Google Scholar 

  154. Fox, K. C. R. et al. Intrinsic network architecture predicts the effects elicited by intracranial electrical stimulation of the human brain. Nat. Hum. Behav. 4, 1039–1052 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  155. Dehaene, S. & Naccache, L. Towards a cognitive neuroscience of consciousness: basic evidence and a workspace framework. Cognition 79, 1–37 (2001).

    Article  CAS  PubMed  Google Scholar 

  156. Sergent, C., Baillet, S. & Dehaene, S. Timing of the brain events underlying access to consciousness during the attentional blink. Nat. Neurosci. 8, 1391–1400 (2005).

    Article  CAS  PubMed  Google Scholar 

  157. Mediano, P. A. M., Seth, A. K. & Barrett, A. B. Measuring integrated information: comparison of candidate measures in theory and simulation. Entropy 21, 17 (2019).

    Article  Google Scholar 

  158. Casali, A. G. et al. A theoretically based index of consciousness independent of sensory processing and behavior. Sci. Transl. Med. 5, 198ra105 (2013). This empirical study shows that a measure of the complexity of the cortical response to transcranial magnetic stimulation distinguishes between a range of global conscious states, including disorders of consciousness.

    Article  PubMed  Google Scholar 

  159. Luppi, A. I. et al. Consciousness-specific dynamic interactions of brain integration and functional diversity. Nat. Commun. 10, 4616 (2019).

    Article  PubMed  PubMed Central  CAS  Google Scholar 

  160. Hardstone, R. et al. Long-term priors influence visual perception through recruitment of long-range feedback. Nat. Commun. 12, 6288 (2021).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  161. de Lange, F. P., Heilbron, M. & Kok, P. How do expectations shape perception? Trends Cogn. Sci. 22, 764–779 (2018).

    Article  PubMed  Google Scholar 

  162. Melloni, L., Schwiedrzik, C. M., Muller, N., Rodriguez, E. & Singer, W. Expectations change the signatures and timing of electrophysiological correlates of perceptual awareness. J. Neurosci. 31, 1386–1396 (2011). This empirical study uses a perceptual hysteresis paradigm to show that expectations enhance and accelerate conscious perception.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  163. Pinto, Y., van Gaal, S., de Lange, F. P., Lamme, V. A. & Seth, A. K. Expectations accelerate entry of visual stimuli into awareness. J. Vis. 15, 13 (2015).

    Article  PubMed  Google Scholar 

  164. Chalmers, D. J. Facing up to the problem of consciousness. J. Conscious. Stud. 23, 200–219 (1995). This work presents the classic statement of the philosophical distinction between the ‘hard’ and ‘easy’ problems of consciousness.

    Google Scholar 

  165. Levine, J. Materialism and qualia: the explanatory gap. Pac. Philos. Q. 64, 354–361 (1983).

    Article  Google Scholar 

  166. Seth, A. K. The Real Problem (Aeon, 2016).

  167. Balog, K. in The Oxford Handbook of Philosophy of Mind (eds Beckermann, A., McLaughlin, B. P., & Walter S.) 292–312 (Oxford Univ. Press, 2009).

  168. Perry, J. Knowledge, Possibility, and Consciousness (MIT Press, 2001).

  169. Varela, F. J., Thompson, E. & Rosch, E. The Embodied Mind: Cognitive Science and Human Experience (MIT Press, 1993).

  170. Carvalho, G. B. & Damasio, A. Interoception and the origin of feelings: a new synthesis. Bioessays 43, e2000261 (2021).

    Article  PubMed  Google Scholar 

  171. Solms, M. The Hidden Spring: A Journey to the Source of Consciousness (Profile Books, 2021).

  172. Merker, B. Consciousness without a cerebral cortex: a challenge for neuroscience and medicine. Behav. Brain Sci. 30, 63–81; discussion 81–134 (2007).

    Article  PubMed  Google Scholar 

  173. Parvizi, J. & Damasio, A. Consciousness and the brainstem. Cognition 79, 135–160 (2001).

    Article  CAS  PubMed  Google Scholar 

  174. Naber, M., Frassle, S. & Einhauser, W. Perceptual rivalry: reflexes reveal the gradual nature of visual awareness. PLoS ONE 6, e20910 (2011).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  175. Casarotto, S. et al. Stratification of unresponsive patients by an independently validated index of brain complexity. Ann. Neurol. 80, 718–729 (2016).

    Article  PubMed  PubMed Central  Google Scholar 

  176. Shea, N. & Bayne, T. The vegetative state and the science of consciousness. Br. J. Philos. Sci. 61, 459–484 (2010).

    Article  PubMed  Google Scholar 

  177. Birch, J. The search for invertebrate consciousness. Noûs 56, 133–153 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  178. Phillips, I. The methodological puzzle of phenomenal consciousness. Philos. Trans. R. Soc. Lond. B Biol. Sci. https://doi.org/10.1098/rstb.2017.0347 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

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Acknowledgements

A.K.S. is Co-Director of, and T.B. is a Fellow in, the CIFAR Program on Brain, Mind, and Consciousness. A.K.S. is additionally grateful to the European Research Council (Advanced Investigator Grant 101019254) and the Dr. Mortimer and Theresa Sackler Foundation.

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Glossary

Neural correlates of consciousness

(NCCs). The minimal set of neural events that is jointly sufficient for a conscious state.

Explanatory gap intuitions

Intuitions that there is no prospect of a fully satisfying explanation of consciousness in physical, mechanistic terms.

Adversarial collaborations

Research projects in which proponents of different theories together design an experiment to distinguish their preferred theories, and agree in advance about how the outcome will favour one theory over the other(s).

Global states

Relating to an organism’s overall state of consciousness, usually linked to arousal and behavioural responsiveness, and associated with the ‘level’ of consciousness.

Local states

Relating to particular conscious mental states, such as a conscious perception, emotion or thought. Local states are also often called conscious contents.

Binocular rivalry

A phenomenon in which different images are presented to each eye, and conscious perception alternates between the two images.

Phenomenal character

The experiential nature of a local state, such as the ‘redness’ of an experience of red or the pain of a toothache — sometimes also called qualia.

Meta-representation

A mental representation that has as its target another mental representation

No-report paradigms

Behavioural experiments in which participants do not provide subjective (verbal, behavioural) reports.

Φ

The amount of information specified by a system that is irreducible to that specified by its parts. There are many variations of Φ, each calculated differently and making different assumptions.

Posterior hot zone

A range of brain regions towards the rear of the cortex, including parietal, temporal and occipital areas, as well as regions such as the precuneus.

Complex

In integrated information theory (IIT), a subset of a physical system that underpins a maximum of irreducible integrated information.

Interoceptive predictions

Predictions about the causes of sensory signals originating from within the body (interoception refers to perception of the body ‘from within’).

Unity of consciousness

The fact that that the experiences that a single agent has at a time seem always to occur as the components of a single complex experience.

Cognitive access

A functional property whereby a mental state has access to a wide range of cognitive processes, usually including verbal and/or behavioural report.

Computational (neuro)phenomenology

The use of computational models to account for the phenomenal character of a conscious state in terms of (neural) mechanisms.

The measurement problem

The problem of identifying whether a particular mental state is conscious, or determining whether an organism or other system is, or has the capacity to be, conscious.

Cerebral organoids

Laboratory-grown neural structures that self-organize into systems with cellular and network features resembling aspects of the developing human brain.

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Seth, A.K., Bayne, T. Theories of consciousness. Nat Rev Neurosci 23, 439–452 (2022). https://doi.org/10.1038/s41583-022-00587-4

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