Sleepwalking | What Happens in the Brain When We Walk in Our Sleep?

Sleepwalking, clinically known as somnambulism, is a type of parasomnia—an undesirable behavior that occurs during sleep. Specifically, it is a disorder of arousal that happens during N3 sleep, the deepest stage of non-rapid eye movement (NREM) sleep. From a neuroscientific perspective, sleepwalking represents a hybrid state of consciousness. In this state, parts of the brain are awake while others remain asleep. The motor cortex, which controls movement, is sufficiently active to allow for complex behaviors such as walking, dressing, or even leaving the house. However, the prefrontal cortex, hippocampus, and other regions responsible for rational thought, decision-making, and memory consolidation remain in a state of deep sleep. This dissociation is why individuals can perform complex actions but have no conscious awareness or subsequent memory of the event. The brain is essentially on autopilot, executing learned motor patterns without the engagement of higher cognitive functions.

While the precise cause of sleepwalking is not fully understood, it involves a combination of genetic and environmental factors. There is a strong hereditary component; individuals with a family history of sleepwalking are significantly more likely to experience it. Key triggers are factors that disrupt or deepen N3 sleep. Sleep deprivation is a primary trigger, as the body attempts to compensate by spending more time in deep sleep, increasing the window of opportunity for an arousal disorder. Other common triggers include high stress, fever, alcohol consumption, and certain medications, particularly sedatives or hypnotics. These factors can increase the frequency of partial arousals from deep sleep, where the body becomes active but the mind does not fully awaken, leading to a sleepwalking episode.

The belief that waking a sleepwalker is dangerous is a persistent myth. It is not medically harmful to awaken them. However, abruptly waking someone from a sleepwalking episode can cause significant confusion, disorientation, and fear. Because they are rising from the deepest stage of sleep, their cognitive functions are severely impaired. This can lead to an agitated or even aggressive reaction, not out of malice, but from a state of profound confusion. The safest approach is not to shout or shake them, but to gently guide the individual back to their bed without waking them. This prevents potential injury to both the sleepwalker and the person assisting.

No, a hallmark of somnambulism is amnesia for the event. The individual typically has no recollection of getting out of bed or any actions performed during the episode. This lack of memory is directly linked to the brain's state during N3 sleep. The hippocampus and prefrontal cortex, critical for encoding new memories and providing conscious context to our actions, are largely inactive. Therefore, while the motor systems are functional, the memory-forming circuits are offline, preventing the experience from being stored and later recalled. Any vague, dream-like fragments that are remembered are rare and typically lack coherent detail.

Sleepwalking and night terrors (pavor nocturnus) are both NREM parasomnias, meaning they occur during deep N3 sleep and are accompanied by amnesia. However, they differ significantly in presentation. Sleepwalking is characterized by calm, complex, and seemingly purposeful motor activity with the individual's eyes often open with a blank, glassy stare. In contrast, a night terror is a partial arousal defined by extreme panic. It typically involves a sudden, terrifying scream, intense crying, and signs of extreme autonomic nervous system arousal, such as a racing heart, sweating, and rapid breathing. While a sleepwalker may move around calmly, a person experiencing a night terror often thrashes in bed and is difficult to console, appearing terrified of an unseen threat. The core distinction lies in the emotional state: sleepwalking is an act without affect, while a night terror is an experience of pure fear.

Sleepwalking