Sleepwalking, formally known as somnambulism, is a parasomnia involving abnormal behaviors during sleep. It is often misunderstood, as it represents a state between being completely asleep and fully awake. This partial state of arousal raises questions about the sleepwalker’s awareness and physical functions, particularly regarding their eyes.
The Sleepwalker’s Gaze
Sleepwalkers do not blink with the same frequency as a person who is awake. The normal blink rate is necessary for lubricating the eyes and refreshing visual focus, but this function is dramatically reduced during a somnambulistic episode. This results in the well-known “glassy-eyed” or vacant stare, where the eyes are open but appear fixed and unresponsive.
When a person is awake, the brain constantly processes visual information, which drives the reflexive blinking pattern. During sleepwalking, the brain’s areas responsible for full consciousness and sensory processing are largely dormant, suppressing the need for this normal visual maintenance. The eyes are physically capable of remaining open, allowing the sleepwalker to navigate their environment, yet they are not operating under the guidance of a fully attentive brain.
The Underlying Sleep State
Somnambulism is categorized as a disorder of arousal, arising from an incomplete awakening from deep non-rapid eye movement (NREM) sleep. It occurs during stage N3, or slow-wave sleep, which is the deepest phase of the sleep cycle. Episodes typically happen during the first third of the night, when slow-wave sleep is most dominant.
The neurological mechanism is “dissociated arousal,” where parts of the brain exhibit patterns of wakefulness while others remain profoundly asleep. Neuroimaging suggests that the motor centers of the brain, which control movement, are active enough to facilitate complex actions like walking or opening doors. However, the areas responsible for memory, rational thought (the frontal cortex), and full sensory perception remain in a delta-wave-dominated sleep state. This dissociation explains how a person can physically move with their eyes open but have impaired consciousness and no memory of the event.
Other Physical Markers of Somnambulism
Beyond the unusual gaze, several other physical signs accompany a sleepwalking episode, all pointing to the state of partial arousal. The sleepwalker’s movements can appear clumsy, awkward, or gangly, contrasting sharply with the complex actions they sometimes perform. Their face often displays a blank, vacant, or confused expression, reflecting the absence of volitional control.
A person during an episode is also minimally responsive to attempts at communication. They may mumble incoherently or not respond at all to verbal stimuli, highlighting the disconnection between their motor activity and their cognitive awareness. This combination of complex physical activity and a lack of cognitive engagement demonstrates the neurological paradox of somnambulism.
When Sleepwalking Requires Medical Attention
Occasional sleepwalking episodes, especially in children, are common and generally resolve without intervention. However, sleepwalking transitions to a health concern when it occurs frequently, such as more than one or two times a week, or if it persists into adulthood. Any episode that leads to injury to the sleepwalker or others is a sign that a medical consultation is necessary.
A sleep specialist should be consulted if the episodes involve complex or violent behaviors, such as trying to leave the house or driving a car while asleep. The onset or reoccurrence of somnambulism in adulthood may also suggest an underlying sleep disorder, like obstructive sleep apnea, or a link to certain medications. Addressing common triggers, such as chronic sleep deprivation, high stress levels, or fever, can sometimes reduce the frequency and severity of these arousal disorders.