Thalamic Contributions to the State and Contents of Consciousness

Abstract

Consciousness can be conceptualized as varying along at least two dimensions: the global state of consciousness and content of conscious experience. Here we highlight the cellular and systems-level contributions of the thalamus to conscious state, and then argue for thalamic contributions to conscious content, including the integrated, segregated and continuous nature of our experience. We underscore vital, yet distinct, roles for core- and matrix-type thalamic neurons. Through reciprocal interactions with deep-layer cortical neurons, matrix neurons support wakefulness and determine perceptual thresholds; whereas the cortical interactions of core neurons maintain content and enable perceptual constancy. We further propose that conscious integration, segregation and continuity depend on the convergent nature of corticothalamic projections enabling dimensionality reduction, a thalamic reticular nucleus-mediated divisive normalization-like process, and sustained coherent activity in thalamocortical loops, respectively. Overall, we conclude that the thalamus plays a central topological role in brain structures controlling conscious experience.