Zelmann, R., Paulk, A., et al. (2023).
Neuron. Volume 111, (21)
Summary
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 we`re reduced, while variability increased in any type of unconscious state. These changes were more pronounced during anesthesia than sleep and involved different cortical engagement. During sleep, changes were mostly uniformly distributed across the brain, whereas during anesthesia, the prefrontal cortex was the most disrupted, suggesting that the lack of arousability during anesthesia results not from just altered overall physiology but from a disconnection between the prefrontal and other brain areas. These findings provide direct evidence for different neural dynamics during loss of consciousness compared with loss of arousability.
Highlights
• Decreased complexity and connectivity, with increased variability when unconscious
• Changes were more pronounced during propofol-induced general anesthesia than sleep
• During sleep, changes were homogeneously distributed across the human brain
• During anesthesia, substantial prefrontal disconnection is related to lack of arousability
Here is my summary:
State-Dependent Cortical Network Engagement
The human brain undergoes significant changes in its functional organization during different states of consciousness, including wakefulness, sleep, and general anesthesia. This study investigated the neural underpinnings of these state-dependent changes by comparing cortical network engagement during wakefulness, sleep, and propofol-induced general anesthesia.
Prefrontal Cortex Disruption during Anesthesia
The findings revealed that loss of consciousness, whether due to sleep or anesthesia, resulted in reduced information integration and increased response variability compared to wakefulness. However, these changes were more pronounced during anesthesia than sleep. Notably, anesthesia was associated with a specific disruption of the prefrontal cortex (PFC), a brain region crucial for higher-order cognitive functions such as decision-making and self-awareness.
Implications for Understanding Consciousness
These findings suggest that the PFC plays a critical role in maintaining consciousness and that its disruption contributes to the loss of consciousness during anesthesia. The study also highlights the distinct neural mechanisms underlying sleep and anesthesia, suggesting that these states involve different modes of brain function.
