Your guide to 29 wildly different theories of consciousness

The many, many ways researchers hope to solve the toughest mystery in science

By Allison Parshall & Jen Christiansen edited by Seth Fletcher

A series of colorful hexagon data plots on a dark background — Jen Christiansen

This graphic is part of a special report on consciousness. Read the full feature here.

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Theorists have proposed many explanations for consciousness. They are startlingly diverse, with different goals, starting points and even definitions of consciousness. To compare them, researchers surveyed articles suggesting a theoretical model for consciousness that were published between 2007 and 2017 in English or Italian.

Some of these theories have many publications to their name, such as global workspace theories, higher-order theories and integrated information theory, three of the field’s leading models. But having more publications does not mean a theory is supported by stronger evidence—this analysis didn’t weigh the strength of study results. Instead the number of articles most likely reflects the amount of interest each type of theory garnered. This may explain why quantum theories of consciousness, which are fascinating but not yet grounded in much evidence, have been proposed so many times. Predictive processing theories, which are also influential in the field, are notably absent, perhaps because they originated as theories of perception rather than consciousness.

THEORIES INCLUDED IN THE META-ANALYSIS

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The researchers found 68 articles that analyzed theoretical aspects of consciousness and that were published between 2007 and 2017 in English or Italian. Together, they represent 29 different types of theories. More than half (18) were suggested only once, but others garnered more interest.

29 consciousness theories are listed, with an indication of the number articles published for each per year. GWT (9), IIT (8), and Quantum theories (12) had the most action between 2007 and 2017. — Jen Christiansen; Source: “Theoretical Models of Consciousness: A Scoping Review,” by Davide Sattin et al., in *Brain Sciences*, Vol. 11; April 2021 (*data*)

THEORY CHARACTERISTICS

All of these proposals are wildly different, and only some are supported by evidence. The researchers analyzed how each tried to address six dimensions of consciousness: (A) what brain activity correlates with conscious experience, (B) how consciousness relates to other mental faculties such as memory and attention, (C) the clinical treatment of disorders involving consciousness, (D) how levels of consciousness could be measured, (E) how consciousness relates to sensory information, and (F) where subjective experience comes from.

Each of 29 consciousness theories are represented by a hexagon, with index scores rooted in 6 variables represented: The neural correlates of consciousness; the association between consciousness and other cognitive functions; translation from theory to clinical practice; the quantitative measures of consciousness; consciousness, sensory processes and the autonomic nervous system; and subjectivity. This panel holds the first 13.

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