REM stands for rapid eye movement but a great deal happens during REM sleep other than our eyes darting backwards and forwards in fast succession. To fully understand REM sleep, it’s useful to understand the whole sleep cycle.
Types Of Sleep
There are two types of sleep: REM sleep and non-REM sleep. Non-REM sleep is divided into three stages: stage 1 (non-REM1, aka N1) or light sleep; stage 2 (N2) or moderate sleep; and stage 3 (N3) or deep sleep or slow wave sleep.
N1 is the transitional stage between wakefulness and sleep. It lasts from 1-7 minutes, and it is very easy to wake up from this stage. During N1, blood pressure begins to fall, breathing becomes shallow and heart rate becomes regular.
N2 lasts between 10 and 25 minutes. As this sleep stage progresses, body temperature drops and there is a gradual appearance of slow wave brain activity. Blood pressure continues to fall, brain metabolism and gastrointestinal secretions decrease, and heart rate slows down. Throughout the night, this stage makes up the majority of our sleep – approximately 50%. It is still easy to wake up from this stage.
N3 is considered the deepest sleep and consists of slow delta waves. Breathing and heart rate continue to slow down, muscles become more relaxed, blood pressure falls and body temperature decreases further. Sensitivity to light and sound declines. During N3, it is difficult to wake up. If you do wake up during this stage, you will most likely be groggy or disorientated.
Typically, people get between 20-40 minutes of N3 sleep per cycle. However, N3 decreases with each subsequent cycle and occurs mostly in the first third of the night. N3 accounts for at least 20% of a person’s sleep for the night.
N3 sleep is associated with body repair and rejuvenation – tissues, bones and muscles grow or are repaired, and the immune system strengthens.
What Is REM Sleep?
REM sleep occurs about 90 minutes after first falling asleep. If you watch a person closely during REM sleep, you will see their eyes moving backwards and forwards beneath their lids. These movements correspond with people visualizing imagery in their sleep. In other words, they’re dreaming.
REM sleep lasts for about 10 minutes in the first cycle and gets longer and longer in subsequent cycles. During the final cycle it can last for up to one hour. In healthy adults, REM sleep makes up approximately 25% of the entire night’s sleep.
During REM sleep leg and arm muscles are effectively paralyzed, which is believed to be the body’s mechanism for preventing someone from acting out their dreams. The brain is very active in this state; an EEG will show brain waves similar to someone who is awake. Breathing is fast and irregular, and heart rate and blood pressure increase. The brain’s oxygen consumption also increases.
During REM sleep, men might experience penile erections and women clitoral engorgement. A number of sleep disorders are also associated with REM sleep, including nightmares and REM sleep behavior disorder (where people act out their dreams).
REM Sleep Aids Memory Consolidation
Most interestingly, REM sleep plays a role in memory consolidation. Early research looked at REM sleep and declarative memory (the memory of facts and events that can be consciously recalled, or declared). For example, when participants undertook an intensive language course, it was noted that REM sleep increased. The assumption, then, was that REM sleep aided the consolidation of the learned material. Subsequent studies confirm this, but scientists have recently learned that slow wave sleep (N3) also plays a role in long-term memory formation.
REM Sleep Strengthens Coping Skills
REM sleep also strengthens a person’s ability to cope with daily life as well as traumatic events. An assessment of individuals who experienced a traumatic event and who had long bouts of REM sleep did not go on to develop post traumatic stress disorder, but those who had short episodes of REM sleep did.
In another study using animals that were deprived of REM sleep, the results showed that their coping and defensive responses were impaired during threatening situations.
Consequences of Reduced REM Sleep
As the majority of REM sleep occurs in the latter part of the night, sleep deprivation typically encroaches the most on REM sleep. However, alcohol also interferes with REM sleep.
Lack of REM sleep has been linked to:
- Migraines and increased chronic pain.
- Obesity (a study published in the International Journal of Obesity found a link between reduced REM sleep and overweight children).
- Impaired coping skills.
- Impaired memory.
- Increased depression.
- Higher likelihood of anxiety or emotional distress (emotional memories such as stress and anxiety are processed and resolved during REM sleep).
REM sleep, therefore, is a very important part of the sleep cycle.