Eyes glazed and hands outstretched, some sleepwalkers look like they came straight out of a zombie movie. Other sleepwalkers can paint, eat, or even drive—often without any memory of these actions after they wake up. How is it possible for people to do these impressive feats when they should be out cold?

“Sleepwalking is a glitch in the system. Our identity is not in control,” said Dr. Emmanuel During from the Icahn School of Medicine at Mount Sinai in an interview for the NOVA documentary “Your Brain: Who's in Control?”

Sleepwalking—also called somnambulism—is a common type of sleeping disorder that affects up to four percent of adults. Though scientists do not fully understand the exact neuroscience behind sleepwalking, they do know this: Sleepwalking occurs when different parts of your brain are stuck between deep sleep and wakefulness, causing confusion between your brain and body.

Normally, your brain is whirring with activity during the day, but after you doze off, it begins to quiet down. The first few stages of sleep occur as your brain prepares itself for rest, decreasing your ability to react to external stimuli and your muscle activity. Soon, your brainwaves also drop down into slow, monotonous motion. This signals that you’ve entered deep sleep.

During sleepwalking, some parts of the brain are suddenly yanked out of their slumber. These include the motor cortex, which is in charge of movement; the visual cortex, which processes visual information; and additional parts of the brain that coordinate behaviors like balance and speech.

Other areas, however, remain dark. One key region that remains asleep is the prefrontal cortex, the brain’s decision maker. When you’re awake, it’s in charge of self-awareness and deliberate choices. Yet during sleepwalking, the awoken areas can work mostly independently of the prefrontal cortex—which is stuck in such deep sleep that it’s hard to wake up. That results in an inability for rational thought, which means it’s also easier for sleepwalkers to do abnormal or nonsensical things that they otherwise wouldn’t.

In other words, everything that takes place during sleepwalking is happening without the person’s conscious awareness. They look awake, but they are unresponsive. It’s this breakdown in brain function that allows sleepwalkers to perform complex actions, all without knowing what’s going on.

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