“Sleepwalking is a reminder that wake and sleep are not mutually exclusive,” Mark Mahowald, a professor of neurology at the University of Minnesota and a pioneer in understanding sleep behaviors, told me. “The part of your brain that monitors your behavior is asleep, but the parts capable of very complex activities are awake. The problem is that there’s nothing guiding the brain except for basic patterns, your most basic habits. You follow what exists in your head, because you’re not capable of making a choice.”
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Sleepwalkers can behave in complex ways — for instance, they can open their eyes, see, move around, and drive a car or cook a meal — all while essentially unconscious, because the parts of their brain associated with seeing, walking, driving, and cooking can function while they are asleep without input from the brain’s more advanced regions, such as the prefrontal cortex.
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However, as scientists have examined the brains of sleepwalkers, they’ve found a distinction between sleepwalking — in which people might leave their beds and start acting out their dreams or other mild impulses — and something called sleep terrors. When a sleep terror occurs, the activity inside people’s brains is markedly different from when they are awake, semi-conscious, or even sleepwalking.
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Because sleep deactivates the prefrontal cortex and other high cognition areas, when a sleep terror habit is triggered, there is no possibility of conscious intervention. If the fight-or-flight habit is cued by a sleep terror, there is no chance that someone can override it through logic or reason.