The neural basis of consciousness remains unclear, with competing theories disagreeing on the roles of frontal versus posterior cortex and neglecting subcortical influences. To investigate, researchers recorded neural activity from frontal cortex, parietal cortex, striatum, and thalamus in macaques that were awake, sleeping, or anesthetized, and also used thalamic stimulation to rouse them from anesthesia. A measure capturing neural integration (Φ*) robustly correlated with changes in consciousness, unlike measures targeting complexity alone. Machine learning revealed that parietal cortex, striatum, and thalamus contributed more than frontal cortex to decoding consciousness states. These findings emphasize integration between parietal and subcortical structures and challenge a key role for frontal cortex in consciousness.
Neurons in the thalamus and deep cortical layers are most sensitive to changes in consciousness level, consistent across different anesthetic agents and sleep. Deep layer activity is sustained by interactions with the central lateral thalamus. Consciousness also depends on deep layer neurons providing feedback to superficial layers, suggesting long-range feedback and intracolumnar signaling are important. Stimulating the central lateral thalamus in anesthetized macaques effectively restored arousal and wake-like neural processing in a location- and frequency-specific manner. These findings suggest layer-specific thalamocortical correlates of consciousness and inform how targeted deep brain stimulation can alleviate disorders of consciousness.