Opinion | Published:

Integrated information theory: from consciousness to its physical substrate

Nature Reviews Neuroscience volume 17, pages 450461 (2016) | Download Citation

Abstract

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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Acknowledgements

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.).

Author information

Affiliations

  1. Department of Psychiatry, University of Wisconsin, 6001 Research Park Boulevard, Madison, Wisconsin 53719, USA.

    • Giulio Tononi
  2. Department of Psychiatry, University of Wisconsin, 6001 Research Park Boulevard, Madison, Wisconsin 53719 USA; and at the Department of Neurology, University of Wisconsin, 1685 Highland Avenue, Madison, Wisconsin 53705, USA.

    • Melanie Boly
  3. Department of Biomedical and Clinical Sciences 'Luigi Sacco', University of Milan, Via G.B. Grassi 74, Milan 20157, Italy; and at the Instituto Di Ricovero e Cura a Carattere Scientifico, Fondazione Don Carlo Gnocchi, Via A. Capecelatro 66, Milan 20148, Italy.

    • Marcello Massimini
  4. Allen Institute for Brain Science, 615 Westlake Ave N, Seattle, Washington 98109, USA.

    • Christof Koch

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Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Giulio Tononi.

Supplementary information

PDF files

  1. 1.

    Supplementary information S1 (figure)

    Axioms and postulates of IIT.

  2. 2.

    Supplementary information S2 (box)

    IIT Pseudocode

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    Supplementary information S3 (figure)

    Integrated information, neuroanatomy and neurophysiology.

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    Supplementary information S4 (box)

    Neuronal bistability impairs information integration during slow wave sleep

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    Supplementary information S5 (box)

    IIT and other theories of consciousness

Glossary

Achromatopsia

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

Anosognosia

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

Axioms

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.

Complex

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.

Concepts

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.

Elements

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.

Mechanism

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.

Postulates

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).

Purviews

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

Qualia

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

Relations

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

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DOI

https://doi.org/10.1038/nrn.2016.44