What do our eyes do when we sleep? While this time may appear to show our bodies at their most restful, our brain and eyes are actually extremely active. Here is some information on what our brains and eyes are doing during this seemingly quiet time.
Rapid Eye Movement
As we sleep, our brains goes through five different stages, one of which is called rapid eye movement (REM) sleep – the other four are known as non-REM sleep. During REM sleep, our eyes move in various directions very quickly. These eye movements, or saccades, are the fastest recorded movements made by the human body! They are able to reach angular speeds of 900 degrees per second.
REM sleep accounts for about one-fourth of an adult’s sleep cycle, and over half the sleep cycle of an infant. Because our sleep cycle repeats, REM occurs several times in one night. Our sleep cycle begins with non-REM sleep, but we enter REM within the first 90 minutes of falling asleep. The first REM phase lasts about 10 minutes. Each REM phase gets longer, until the final REM phase of the night, which can lasts up to an hour.
During REM, most people reach a state of temporary paralysis, where our brains signal the spinal cord to stop muscle activity in the arms and legs: this is known as atonia. (It is thought that atonia protects us from injury if we were to act out our dreams.) Though the body is quite still at this time, we experience brain activity similar to that we have while awake. Because of this, REM is associated with vivid dreams. REM is sometimes called paradoxical sleep, which describes the strange state where our brains are active while our bodies are immobile.
While the exact reasons our eyes dart around during REM have remained elusive, researchers have found some clues. Recent studies done on volunteer epilepsy patients (who have implants in their medial temporal lobes for treatment) has shown that activity within this region increased a quarter-second after volunteers’ eyes moved. These results led researchers to believe that during REM, the brain changes mental imagery.
The Importance of REM and Quality Sleep
REM is associated with beneficial health effects and is the part of the cycle most associated with sleep quality. In addition, according to the National Sleep Foundation, it is believed that REM sleep benefits memory, learning, and even mood. A lack of REM sleep, then, can have negative implications on emotional and physical health, as well as brain functioning. A deficiency in REM has been linked with migraines, excess weight, and abnormalities in defensive responses and coping mechanisms.
Though it’s a common part of the sleep cycle, REM only occurs once we reach a very deep, or restful, sleep. So if you’re not getting enough sleep, you’re also not getting the beneficial effects of REM. In addition, overall sleep deprivation can affect eye health, as our eyes replenish when we sleep and need at least five hours a night to do so properly. Lack of sleep can lead to popped blood vessels in the eyes, dry eye, spasms, and/or swelling of the optic nerve.
Adults should sleep 7 to 9 hours a night, and kids should sleep 10 to 11 hours – and more for toddlers and babies.