Differential Cortical Network Engagement During States of Un/Consciousness in Humans

Abstract

What happens in the human brain when we are unconscious? Despite substantial work, we are still unsure which brain regions are involved and how they are impacted when consciousness is disrupted. Using intracranial recordings and direct electrical stimulation, we mapped global, network, and regional involvement during wake vs. arousable unconsciousness (sleep) vs. non-arousable unconsciousness (propofol-induced general anesthesia). Information integration and complex processing were reduced, while variability increased in any type of unconscious state. These changes were more pronounced during anesthesia than sleep. They also involved different cortical engagement; During sleep, changes were mostly uniformly distributed across the brain while during anesthesia the prefrontal cortex was the most disrupted, suggesting that the obliteration of consciousness during anesthesia results not from just altered overall physiology but from a disconnection between prefrontal and other brain areas. These findings provide direct evidence of the different neural signatures for different types of unconsciousness.

Convergent effects of different anesthetics are due to changes in phase alignment of cortical oscillations

“…These waves may play an essential role in shaping neural activity when awake [26][27][28][29] , and severely limiting it during anesthesia 25,30 by fragmenting within-hemisphere communication as periods of excitability become misaligned [3][4][5][6][7] . In fact, propofol has been shown to fragment activity and decrease information transfer across long distances (>2 cm) in human cortex [31][32][33] , and to prevent sensory signals from reaching macaque frontal cortex 34 . We note that there was not a complete misalignment of phases at all times, but rather a tendency for LFPs to be out of phase more often.…”

Frontal-posterior loop integrating captured attention into visual consciousness in the human brain

“…Applying the same reasoning, the previous findings [46, 47], seemingly supporting the posterior-centric view of consciousness, might actually arise from posterior activities that are integrated with frontal attention to varying degrees (i.e., robustly versus weakly). In more extreme cases, such as during general anesthesia, a complete functional disconnection between the prefrontal cortex and other brain regions renders the brain entirely unresponsive and unconscious [48].…”