Category Theory Approaches to Consciousness
Key players: Nao Tsuchiya (Monash), Hayato Saigo (Nagahama Institute), Steven Phillips (AIST), Ryota Kanai (Araya).
Tsuchiya & Taguchi (2016)
Using category theory to assess the relationship between consciousness and integrated information theory Neuroscience Research | ScienceDirect | PubMed
Founding paper of this line of work. Proposes breaking IIT into three categorical subprojects: (1) characterise phenomenal structure as a category, (2) characterise integrated information as a category, (3) assess whether a structure-preserving functor exists between them. If it does, hard questions about consciousness could be resolved mathematically.
Northoff & Tsuchiya (2019)
Mathematics and the Brain: A Category Theoretical Approach to Go Beyond the Neural Correlates of Consciousness Frontiers in Psychology | Semantic Scholar
Argues that the NCC project is fundamentally limited and that category theory provides tools to go beyond correlation — mapping structure between brain and phenomenal domains via functors rather than just identifying co-varying neural signatures.
Tsuchiya & Saigo (2021)
A relational approach to consciousness: categories of level and contents of consciousness Neuroscience of Consciousness | Oxford Academic | PMC
Defines a “category of consciousness” where objects are conscious states and morphisms encode similarity/subsumption relations. Uses the Yoneda lemma to argue that a conscious state is fully characterised by all its relations to other states — not by intrinsic properties. Introduces enriched categories to handle graded similarity. Separates the project into a “category of the brain” and a “category of consciousness” to be related in a later step.
Tsuchiya, Saigo & Phillips (2022)
An adjunction hypothesis between qualia and reports Frontiers in Psychology | Full text | PMC
Proposes that the relationship between qualia and verbal/behavioural reports is an adjunction — a weaker, more flexible correspondence than an isomorphism. The left adjoint maps reports to qualia; the right adjoint maps qualia to reports. This formalises why introspective reports are systematically related to experience but never perfectly faithful. Ryota Kanai (Araya) contributed as editor.
Tsuchiya et al. (2024)
Category theory in consciousness science: going beyond the correlational project Synthese | Springer
Most recent synthesis. Reviews the categorical programme and argues it enables a structural rather than merely correlational science of consciousness. Discusses how functors, natural transformations, and adjunctions operationalise theoretical claims in IIT, Global Workspace, and relational approaches.