Integrated information theory: from consciousness to its physical substrate


In this Opinion article, we discuss how integrated information theory accounts for several aspects of the relationship between consciousness and the brain. Integrated information theory starts from the essential properties of phenomenal experience, from which it derives the requirements for the physical substrate of consciousness. It argues that the physical substrate of consciousness must be a maximum of intrinsic cause–effect power and provides a means to determine, in principle, the quality and quantity of experience. The theory leads to some counterintuitive predictions and can be used to develop new tools for assessing consciousness in non-communicative patients.

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Figure 1: An experience is a conceptual structure.
Figure 2: Identifying the elements, timescale and states of the physical substrate of consciousness (PSC) from first principles.
Figure 3: Identifying the physical substrate of consciousness (PSC) from first principles.
Figure 4: Phenomenal content and access content.


  1. 1

    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).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  2. 2

    Tononi, G. The integrated information theory of consciousness: an updated account. Arch. Ital. Biol. 150, 56–90 (2012).

    CAS  PubMed  Google Scholar 

  3. 3

    Tononi, G. Integrated information theory. Scholarpedia (2015).

    Google Scholar 

  4. 4

    Posner, J. B., Saper, C. B., Schiff, N. D. & Plum, F. Diagnosis of Stupor and Coma (Oxford Univ. Press, 2007).

    Google Scholar 

  5. 5

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

    CAS  PubMed  Article  Google Scholar 

  6. 6

    Boly, M. et al. Consciousness in humans and non-human animals: recent advances and future directions. Front. Psychol. 4, 625 (2013).

    PubMed  PubMed Central  Article  Google Scholar 

  7. 7

    Lemon, R. N. & Edgley, S. A. Life without a cerebellum. Brain 133, 652–654 (2010).

    CAS  PubMed  Article  Google Scholar 

  8. 8

    Yu, F., Jiang, Q. J., Sun, X. Y. & Zhang, R. W. A new case of complete primary cerebellar agenesis: clinical and imaging findings in a living patient. Brain 138, e353 (2015).

    PubMed  Article  Google Scholar 

  9. 9

    Tononi, G. & Koch, C. Consciousness: here, there, and everywhere? Phil. Trans. R. Soc. B 370, 20140167 (2015).

    PubMed  Article  Google Scholar 

  10. 10

    Chalmers, D. J. Facing up to the problem of consciousness. J. Conscious. Studies 2, 200–219 (1995).

    Google Scholar 

  11. 11

    Tononi, G. An information integration theory of consciousness. BMC Neurosci. 5, 42 (2004).

    PubMed  PubMed Central  Article  Google Scholar 

  12. 12

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

    PubMed  Article  Google Scholar 

  13. 13

    Descartes, R. Discourse on Method and Meditations on First Philosophy (Hackett, 1998).

    Google Scholar 

  14. 14

    Pöppel, E. Mindworks: Time and Conscious Experience (Harcourt Brace Jovanovich, 1988).

    Google Scholar 

  15. 15

    Holcombe, A. O. Seeing slow and seeing fast: two limits on perception. Trends Cogn. Sci. 13, 216–221 (2009).

    PubMed  Article  Google Scholar 

  16. 16

    Bachmann, T. Microgenetic Approach to the Conscious Mind (John Benjamins, 2000).

    Google Scholar 

  17. 17

    Kim, J. Multiple realization and the metaphysics of reduction. Philos. Phenomenol. Res. 52, 1–26 (1992).

    CAS  Article  Google Scholar 

  18. 18

    Hoel, E. P., Albantakis, L. & Tononi, G. Quantifying causal emergence shows that macro can beat micro. Proc. Natl Acad. Sci. USA 110, 19790–19795 (2013).

    CAS  PubMed  Article  Google Scholar 

  19. 19

    Alivisatos, A.P. et al. The brain activity map project and the challenge of functional connectomics. Neuron 74, 970–974 (2012).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  20. 20

    Buzsáki, G. Neural syntax: cell assemblies, synapsembles, and readers. Neuron 68, 362–385 (2010).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  21. 21

    Li, C. Y., Poo, M. M. & Dan, Y. Burst spiking of a single cortical neuron modifies global brain state. Science 324, 643–646 (2009).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  22. 22

    London, M., Roth, A., Beeren, L., Häusser, M. & Latham, P. E. Sensitivity to perturbations in vivo implies high noise and suggests rate coding in cortex. Nature 466, 123–127 (2010).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  23. 23

    Boly, M. et al. Stimulus set meaningfulness and neurophysiological differentiation: a functional magnetic resonance imaging study. PLoS ONE 10, e0125337 (2015).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  24. 24

    Boly, M. et al. Brain connectivity in disorders of consciousness. Brain Connect. 2, 1–10 (2012).

    Article  Google Scholar 

  25. 25

    Seth, A. K., Barrett, A. B. & Barnett, L. Causal density and integrated information as measures of conscious level. Philos. Trans. A Math. Phys. Eng. Sci. 369, 3748–3767 (2011).

    PubMed  Article  Google Scholar 

  26. 26

    Deco, G., Hagmann, P., Hudetz, A. G. & Tononi, G. Modeling resting-state functional networks when the cortex falls asleep: local and global changes. Cereb. Cortex 24, 3180–3194 (2014).

    PubMed  Article  Google Scholar 

  27. 27

    von Arx, S. W., Muri, R. M., Heinemann, D., Hess, C. W. & Nyffeler, T. Anosognosia for cerebral achromatopsia — a longitudinal case study. Neuropsychologia 48, 970–977 (2010).

    PubMed  Article  Google Scholar 

  28. 28

    Goldberg, I. I., Harel, M. & Malach, R. When the brain loses its self: prefrontal inactivation during sensorimotor processing. Neuron 50, 329–339 (2006).

    CAS  PubMed  Article  Google Scholar 

  29. 29

    Steriade, M., Timofeev, I. & Grenier, F. Natural waking and sleep states: a view from inside neocortical neurons. J. Neurophysiol. 85, 1969–1985 (2001).

    CAS  Article  Google Scholar 

  30. 30

    Nir, Y. et al. Regional slow waves and spindles in human sleep. Neuron 70, 153–169 (2011).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  31. 31

    Siclari, F., LaRocque, J. J., Bernardi, G., Postle, B. R. & Tononi, G. The neural correlates of consciousness in sleep: a no-task, within-state paradigm. BioRXiv (2014).

  32. 32

    Sperry, R. W. in Neuroscience 3rd Study Program (eds Schmitt, F. O. & Worden, F. G.) 5–19 (MIT Press, 1974).

    Google Scholar 

  33. 33

    Gazzaniga, M. S. Forty-five years of split-brain research and still going strong. Nat. Rev. Neurosci. 6, 653–659 (2005).

    CAS  Article  Google Scholar 

  34. 34

    Berlin, H. A. The neural basis of the dynamic unconscious. Neuropsychoanalysis 13, 1–68 (2011).

    Google Scholar 

  35. 35

    Mudrik, L., Breska, A., Lamy, D. & Deouell, L. Y. Integration without awareness: expanding the limits of unconscious processing. Psychol. Sci. 22, 764–770 (2011).

    PubMed  Article  Google Scholar 

  36. 36

    Mudrik, L., Faivre, N. & Koch, C. Information integration without awareness. Trends Cogn. Sci. 18, 488–496 (2014).

    PubMed  Article  Google Scholar 

  37. 37

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

    CAS  PubMed  Article  Google Scholar 

  38. 38

    Harris, K. D. & Shepherd, G. M. The neocortical circuit: themes and variations. Nat. Neurosci. 18, 170–181 (2015).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  39. 39

    Miller, G. A. The magical number seven, plus or minus two: some limits on our capacity for processing information. Psychol. Rev. 63, 81–97 (1956).

    CAS  PubMed  Article  Google Scholar 

  40. 40

    Norretranders, T. The User Illusion: Cutting Consciousness Down to Size (Viking Penguin, 1991).

    Google Scholar 

  41. 41

    Sperling, G. The information available in brief visual presentations. Psychol. Monogr. 74, 1–29 (1960).

    Article  Google Scholar 

  42. 42

    Cohen, M. A. & Dennett, D. C. Consciousness cannot be separated from function. Trends Cogn. Sci. 15, 358–364 (2011).

    PubMed  Article  Google Scholar 

  43. 43

    Cohen, M. A. & Dennett, D. C. Response to Fahrenfort and Lamme: defining reportability, accessibility and sufficiency in conscious awareness. Trends Cogn. Sci. 16, 139–140 (2012).

    Article  Google Scholar 

  44. 44

    O'Regan, J. K., Rensink, R. A. & Clark, J. J. Change-blindness as a result of 'mudsplashes'. Nature 398, 34–34 (1999).

    CAS  PubMed  Article  Google Scholar 

  45. 45

    Dehaene, S. Consciousness and the Brain: Deciphering How the Brain Codes our Thoughts (Penguin, 2014).

    Google Scholar 

  46. 46

    Kouider, S., de Gardelle, V., Sackur, J. & Dupoux, E. How rich is consciousness? The partial awareness hypothesis. Trends Cogn. Sci. 14, 301–307 (2010).

    PubMed  Article  Google Scholar 

  47. 47

    Block, N. On a confusion about a function of consciousness. Behav. Brain Sci. 18, 227–287 (1995).

    Article  Google Scholar 

  48. 48

    Block, N. Perceptual consciousness overflows cognitive access. Trends Cogn. Sci. 15, 567–575 (2011).

    PubMed  Article  Google Scholar 

  49. 49

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

    PubMed  Article  Google Scholar 

  50. 50

    Bronfman, Z. Z., Brezis, N., Jacobson, H. & Usher, M. We see more than we can report: “cost free” color phenomenality outside focal attention. Psychol. Sci. 25, 1394–1403 (2014).

    PubMed  Article  Google Scholar 

  51. 51

    Wolfe, J. in Fleeting Memories (ed. Coltheart, V.) 71–94 (MIT Press, 2000).

    Google Scholar 

  52. 52

    Felleman, D. J. & Van Essen, D. C. Distributed hierarchical processing in the primate cerebral cortex. Cereb. Cortex 1, 1–47 (1991).

    CAS  PubMed  Article  Google Scholar 

  53. 53

    Riesenhuber, M. & Poggio, T. Hierarchical models of object recognition in cortex. Nat. Neurosci. 2, 1019–1025 (1999).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  54. 54

    Franzius, M., Sprekeler, H. & Wiskott, L. Slowness and sparseness lead to place, head-direction, and spatial-view cells. PLoS Comput. Biol. 3, e166 (2007).

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  55. 55

    Spratling, M. W. Learning posture invariant spatial representations through temporal correlations. IEEE Trans. Autonom. Ment. Dev. 1, 253–263 (2009).

    Article  Google Scholar 

  56. 56

    Treisman, A. The binding problem. Curr. Opin. Neurobiol. 6, 171–178 (1996).

    CAS  PubMed  Article  Google Scholar 

  57. 57

    Baddeley, A. D. Working Memory (Clarendon Press, 1986).

    Google Scholar 

  58. 58

    Herculano-Houzel, S. The remarkable, yet not extraordinary, human brain as a scaled-up primate brain and its associated cost. Proc. Natl Acad. Sci. USA 109 (Suppl. 1), 10661–10668 (2012).

    CAS  PubMed  Article  Google Scholar 

  59. 59

    Jain, S. K. et al. Bilateral large traumatic basal ganglia haemorrhage in a conscious adult: a rare case report. Brain Inj. 27, 500–503 (2013).

    CAS  PubMed  Article  Google Scholar 

  60. 60

    Straussberg, R. et al. Familial infantile bilateral striatal necrosis: clinical features and response to biotin treatment. Neurology 59, 983–989 (2002).

    CAS  PubMed  Article  Google Scholar 

  61. 61

    Caparros-Lefebvre, D., Destee, A. & Petit, H. Late onset familial dystonia: could mitochondrial deficits induce a diffuse lesioning process of the whole basal ganglia system? J. Neurol. Neurosurg. Psychiatry 63, 196–203 (1997).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  62. 62

    Pigorini, A. et al. Bistability breaks-off deterministic responses to intracortical stimulation during non-REM sleep. Neuroimage 112, 105–113 (2015).

    PubMed  Article  Google Scholar 

  63. 63

    Blumenfeld, H. Impaired consciousness in epilepsy. Lancet Neurol. 11, 814–826 (2012).

    PubMed  PubMed Central  Article  Google Scholar 

  64. 64

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

    CAS  PubMed  Article  Google Scholar 

  65. 65

    Edlund, J. A. et al. Integrated information increases with fitness in the evolution of animats. PLoS Comput. Biol. 7, e1002236 (2011).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  66. 66

    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).

    PubMed  PubMed Central  Article  Google Scholar 

  67. 67

    Massimini, M. et al. Breakdown of cortical effective connectivity during sleep. Science 309, 2228–2232 (2005).

    CAS  PubMed  Article  Google Scholar 

  68. 68

    Casali, A. G. et al. A theoretically based index of consciousness independent of sensory processing and behavior. Sci. Transl Med. 5, 198ra105 (2013).

    PubMed  Article  Google Scholar 

  69. 69

    Massimini, M. et al. Cortical reactivity and effective connectivity during REM sleep in humans. Cogn. Neurosci. 1, 176–183 (2010).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  70. 70

    Sarasso, S. et al. Consciousness and complexity during unresponsiveness induced by propofol, xenon, and ketamine. Curr. Biol. 25, 3099–3105 (2015).

    CAS  PubMed  Article  Google Scholar 

  71. 71

    Barrett, A. B. & Seth, A. K. Practical measures of integrated information for time-series data. PLoS Comput. Biol. 7, e1001052 (2011).

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  72. 72

    Oizumi, M., Amari, S., Yanagawa, T., Fujii, N. & Tsuchiya, N. Measuring integrated information from the decoding perspective. PLoS Comput Biol 12, e1004654 (2015).

    Article  CAS  Google Scholar 

  73. 73

    Hudetz, A. G., Liu, X. & Pillay, S. Dynamic repertoire of intrinsic brain states is reduced in propofol-induced unconsciousness. Brain Connect. 5, 10–22 (2015).

    PubMed  PubMed Central  Article  Google Scholar 

  74. 74

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

    CAS  PubMed  Article  Google Scholar 

  75. 75

    Tagliazucchi, E. et al. Large-scale signatures of unconsciousness are consistent with a departure from critical dynamics. J. R. Soc. Interface 13, 20151027 (2016).

    PubMed  PubMed Central  Article  Google Scholar 

  76. 76

    Sullivan, P. R. Contentless consciousness and information-processing theories of mind. Philos. Psychiatry Psychol. 2, 51–59 (1995).

    Google Scholar 

  77. 77

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

    Google Scholar 

  78. 78

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

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  79. 79

    Steriade, M. The corticothalamic system in sleep. Front. Biosci. 8, d878-99 (2003).

    PubMed  Article  Google Scholar 

  80. 80

    Searle, J. Can information theory explain consciousness? New York Review of Books (10 Jan 2013).

    Google Scholar 

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The authors thank L. Albantakis, C. Cirelli, L. Ghilardi, W. Marshall, W. Mayner, A. Mensen, M. Oizumi, U. Olcese, B. Postle, S. Sasai and other colleagues for their various contributions to the work presented here. This work was supported by the Templeton World Charity Foundation, the McDonnell Foundation and the Distinguished Chair in Consciousness Science (University of Wisconsin) (to G.T.), and by the James S. McDonnell Scholar Award 2013 (to M.M.).

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Correspondence to Giulio Tononi.

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Integrated Information Theory

PowerPoint slides

Supplementary information

Supplementary information S1 (figure)

Axioms and postulates of IIT. (PDF 340 kb)

Supplementary information S2 (box)

IIT Pseudocode (PDF 135 kb)

Supplementary information S3 (figure)

Integrated information, neuroanatomy and neurophysiology. (PDF 219 kb)

Supplementary information S4 (box)

Neuronal bistability impairs information integration during slow wave sleep (PDF 842 kb)

Supplementary information S5 (box)

IIT and other theories of consciousness (PDF 322 kb)



A condition in which a person is unable to perceive colours.


A condition in which a person has a neurological deficit, but is unaware of it.


Properties that are self-evident and essential; in integrated information theory, those that are true of every possible experience — namely, intrinsic existence, composition, information, integration and exclusion.

Background conditions

Factors that enable consciousness, such as neuromodulators and external inputs that maintain adequate excitability.

Cause–effect repertoire

The probability distribution of potential past and future states of a system that is specified by a mechanism in its current state.

Cause–effect space

A space with each axis representing the probability of each possible past and future state of a system.

Cause–effect structure

The set of cause–effect repertoires specified by all the mechanisms of a system in its current state.


A set of elements in a state that specifies a conceptual structure corresponding to a maximum of integrated information (Φmax). A complex is thus a physical substrate of consciousness.


The cause–effect repertoires specified by a mechanism that is maximally irreducible (Φmax).

Conceptual structure

The set of all concepts specified by a system of elements in a state with their respective Φmax values, which can be plotted as a set of points in cause–effect space.

Content-specific NCC

Neural elements, the activity of which determines a particular content of experience.


The minimum constituents of a system that have at least two different states (for example, being on or off), inputs that can affect those states and outputs that depend on them.

Full NCC

The neural elements constituting the physical substrate of consciousness, irrespective of its specific content.

Integrated information

(Denoted Φ). Information that is specified by a system that is irreducible to that specified by its parts. It is calculated as the distance between the conceptual structure specified by the intact system and that specified by its minimum information partition.


Any subset of elements within a system that has cause–effect power on it (that is, that constrains its cause–effect space).

Neural correlates of consciousness

(NCC). The minimum neuronal mechanisms jointly sufficient for any one specific conscious experience.


Properties of experience that are derived from the axioms of integrated information theory and that must be satisfied by the physical substrate of consciousness — namely, to be a maximum of irreducible, specific, compositional, intrinsic cause–effect power (intrinsic cause–effect power for short).


The subsets of elements of a complex, the past and future states of which are constrained by a mechanism specifying a concept.


The qualitative feeling of phenomenal distinctions within an experience (for example, seeing a colour, hearing a sound or feeling a pain).


Maximally irreducible overlaps among the purviews of two or more concepts.

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Tononi, G., Boly, M., Massimini, M. et al. Integrated information theory: from consciousness to its physical substrate. Nat Rev Neurosci 17, 450–461 (2016).

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