Eye movements, including those that appear as rolling, are a normal part of the sleep cycle. Their occurrence varies significantly depending on the specific sleep stage.
Understanding Eye Movements Across Sleep Stages
Sleep is broadly categorized into two main types: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. Our bodies cycle through these types multiple times each night, with each full cycle lasting approximately 90 to 120 minutes. Eye activity differs considerably between these phases.
NREM sleep, which comprises about 75% of total sleep time, is further divided into three stages. During the initial stages of NREM sleep, such as Stage 1, eye movements tend to slow down. As sleep deepens into Stage 2 and Stage 3 (also known as deep sleep), eye movements typically become minimal or cease altogether. In these deeper NREM stages, the parasympathetic nervous system is active, causing pupils to constrict and further limiting visual input.
In contrast, REM sleep is characterized by distinct and vigorous eye movements. The eyes move rapidly and randomly beneath closed eyelids during this stage. This phase is also marked by increased brain activity, similar to wakefulness, and is when vivid dreaming most frequently occurs. Adults usually spend 20% to 25% of their total sleep time in REM sleep, with longer periods occurring later in the night.
Theories Behind Eye Rolling During Sleep
Researchers have long been fascinated by the rapid eye movements during REM sleep, leading to several theories about their purpose. One prominent explanation is the “scanning hypothesis,” suggesting these movements correspond to a person’s gaze within their dream imagery. This theory proposes the eyes “scan” the dream’s virtual environment, similar to surveying a scene while awake. Studies, including those on individuals with REM sleep behavior disorder, have shown a correlation between eye movement direction and dream content.
The scanning hypothesis is not universally accepted, and other perspectives exist. Evidence challenges this theory, noting that rapid eye movements still occur in individuals blind since birth who do not experience visual dreams. Another theory points to pontine-geniculate-occipital (PGO) waves. These bursts of electrical activity originate in the brainstem, travel to the thalamus, and then to the occipital cortex. PGO waves are a consistent feature of REM sleep, closely associated with generating rapid eye movements, suggesting they are a byproduct of intrinsic brainstem activity rather than directly linked to visual dream content.
Is Eye Rolling During Sleep Normal?
Observing eye movements, including apparent rolling, during sleep is a normal physiological phenomenon. This is particularly true during REM sleep, where eyes exhibit rapid, jerky motions. These movements are an expected component of healthy brain activity during this active sleep stage.
Subtle eye rolling can also occur as a person drifts into the initial stages of sleep, where muscle relaxation can lead to the eyes slowly turning upwards. This is a natural transition as the body prepares for deeper sleep. These movements are simply a visible manifestation of the complex and dynamic processes occurring within the brain during sleep.