The idea that our eyes “go back” into our heads when we sleep is a common misconception. While eyes do not literally retract, they exhibit specific movements or stillness depending on the stage of sleep. Understanding what actually happens to our eyes during sleep provides insight into the complex processes our brains undergo each night. These movements are not random but are tied to the different phases of our sleep cycle.
Understanding Sleep Stages
Sleep is not a uniform state of rest but rather a progression through distinct stages, broadly categorized into Non-Rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) sleep, with a typical cycle lasting approximately 90 to 120 minutes in adults. NREM sleep, which usually occurs first, consists of three stages, each progressively deeper. Stage 1 is a light, transitional phase where brain activity begins to slow down, and it is easy to be awakened. Stage 2 sees a continued slowing of body activity, with eye movements ceasing. The deepest NREM stage, Stage 3, is characterized by very slow brain waves, and it is difficult to wake someone from this restorative period.
Eye Movement During REM Sleep
Rapid Eye Movement (REM) sleep is a unique phase characterized by distinct eye movements behind closed eyelids, known as saccades. REM sleep is also known as “paradoxical sleep” because, despite the body being largely still due to temporary muscle paralysis, the brain shows activity similar to wakefulness. This muscle paralysis, called atonia, prevents individuals from acting out their dreams. The eyes move rapidly and irregularly in various directions during REM sleep. Research suggests these eye movements might correspond to the visual experiences within dreams, helping the brain process and integrate visual information. Brain activity during REM sleep is also linked to memory consolidation and emotional processing.
Eye Movement During NREM Sleep
During Non-Rapid Eye Movement (NREM) sleep, eye movements are considerably different from those observed in REM sleep. As a person transitions into the initial stages of NREM sleep, eyes may exhibit very slow, rolling movements. As sleep deepens into NREM Stage 2 and Stage 3, eye movements usually stop altogether. The eyes become relatively quiescent during these deeper stages, reflecting the overall reduction in brain and body activity. This stillness contrasts sharply with the dynamic, rapid eye movements characteristic of REM sleep.
Addressing Common Beliefs
The notion that eyes “go back” into the head during sleep is a visual misinterpretation. The eyes remain within their sockets throughout sleep. What might appear as eyes rolling back is often an upward rotation, which can occur as a natural reflex when the eyelids close. This upward movement, known as Bell’s reflex, can also serve as a protective mechanism for the cornea. Sometimes, observing a sleeping person’s eyes through slightly parted eyelids can reveal eye movements, which might contribute to the “rolling back” perception. These observed movements are internal and do not mean the eyes are retracting. The movements are simply the internal processes associated with different sleep stages becoming visible.