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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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.
The authors declare no competing interests.
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- 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.
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.
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.
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