Same Brain, Different States: Waking, Sleeping, and Anesthesia
Same Brain, Different States: Waking, Sleeping, and Anesthesia
This chapter examines dynamic states in which brain systems differentially express their involvement in conscious versus nonconscious representation. Given the evidence for a role of corticothalamic systems in consciousness, in what kind of state should they be to do so? Reviewing the neurophysiology of sleep, anaesthesia and wakefulness, a diverse picture of brain dynamics emerges in association with conscious processing. Comparing sleep with wakefulness, we see evidence for the primary role of so-called Up states in the neocortex, featuring high levels of depolarization, irregular firing, and desynchronized EEG. Pathophysiological and computational studies emphasize the importance of having decorrelated activity rather than global synchrony. Studies on "replay" during sleep or wakefulness show that this phenomenon unlikely corresponds to conscious processing, challenging simple implementations of “neural coalitions” embodying consciousness. Findings on anesthesia highlight the prominence of sustaining long-range rather than local interactions between distributed cell assemblies. On the fast time scale of perception, recurrent interactions from higher to lower cortical levels are probably important, yet more work is needed to find out which connectivity components are essential for perception or behavioral reporting. In EEG research on perception, alpha oscillations are emerging in regulating the phasing of stimulus perceptibility.
Keywords: Assembly, Coalition, Desynchronization, Dream, Long-range connectivity, Microgenesis, Oscillation, Rapid eye movement sleep, Replay, Slow-wave sleep
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