The intralaminar and medial thalamic nuclei act as a gate to drive prefrontal cortex activity during the emergence of conscious perception. In patients with implanted electrodes performing a visual consciousness task, these nuclei showed earlier and stronger consciousness-related activity compared to ventral nuclei and prefrontal cortex. Transient thalamofrontal neural synchrony and cross-frequency coupling were driven by the θ phase of the intralaminar and medial nuclei during conscious perception.
Saccadic latency is significantly shorter when people are aware of a visual stimulus than when they are unaware. Local field potential recordings from the prefrontal cortex of six patients show early awareness-related activity, including event-related potentials and high-gamma activity, between 200 and 300 milliseconds. The neural activity in the prefrontal cortex can reliably decode the awareness state from an early stage, and the neural pattern changes dynamically rather than remaining stable during awareness. Enhanced dynamic functional connectivity through low-frequency phase modulation between the prefrontal cortex and other brain regions in early awareness trials may explain the mechanism of conscious access. These results indicate that the prefrontal cortex is critically involved in the emergence of awareness.
Consciousness-related neural activity in the human brain can be separated into two processes: phenomenal consciousness (early, brief awareness) and access consciousness (later, reportable awareness). Using electrodes implanted in epilepsy patients, researchers found that visual awareness-related brain signals appeared at two distinct latencies—short and long—that originate from different brain regions, except in the lateral prefrontal cortex, where both types mix. Early activity was confined to the side of the brain opposite the visual stimulus, while late activity appeared on both sides. Information flowed from early to late sites, supporting a two-stage model of conscious perception and providing the first direct evidence from intracranial recordings for this division.