Understanding Rem Sleep: Its Vital Functions And Benefits

Sleep is a complex and mysterious body process, and while we know that it allows our body and brain to rest, the exact reasons why we sleep and what happens while we sleep are still not fully understood. Sleep can be divided into two stages: REM (rapid eye movement) and NREM (non-rapid eye movement). NREM is further split into three parts: starting to fall asleep, light sleep, and deep sleep. During the REM stage, our eyes move rapidly and our muscles become temporarily paralysed. This is the stage in which most of our vivid dreaming takes place. REM sleep is important for brain health and function, and plays a significant role in memory consolidation, emotional processing, brain development, and dreaming.

Dreaming and memory consolidation

REM sleep is associated with vivid dreaming. While dreams can occur during non-REM sleep, they are typically more intense and narrative during REM sleep. The dreams experienced during this stage may be linked to the memory consolidation process, as they often incorporate elements of the dreamer's recent experiences and episodic memory.

The function of dreaming during REM sleep is not yet fully understood, but several theories have been proposed. One theory, known as the "scanning hypothesis," suggests that the directional properties of REM sleep are related to shifts in gaze during dream imagery. Another theory, proposed by Graeme Mitchison and Francis Crick, suggests that the spontaneous activity of the brain during REM sleep serves to "unlearn" or remove undesirable modes of interaction in neural networks, strengthening relevant memories and allowing weaker ones to disintegrate.

REM sleep is also believed to aid in brain development, particularly in infants and newborns, who spend a significant portion of their sleep in this stage. The high prevalence of REM sleep in early life may be linked to the development of the central nervous system, including the brain and spinal cord.

In summary, REM sleep plays a crucial role in dreaming and memory consolidation. While the exact mechanisms are still being explored, it is clear that this stage of sleep is essential for processing and storing new information, as well as regulating our mental and emotional well-being.

Emotional processing

REM sleep is associated with increased activation in emotion-related structures like the amygdala and hippocampus, which offer an opportunity to reactivate and process emotional experiences. The predominance of theta waves during REM sleep leads to large-scale networks that allow a contextual integration of these experiences into existing memory structures. Moreover, aminergic neurotransmitters that are linked to stressful and anxious states are largely absent during REM sleep, which may facilitate neural decoupling of declarative information and emotional connotation.

REM sleep may increase reactivity to emotional stimuli in the short term and this effect of REM sleep appears to facilitate emotional processing during subsequent nights, leading to reduced intrusive picture memories in the long term.

Brain development

REM sleep is important for brain development, particularly in newborns. Newborns spend about half of their sleep time in REM sleep, which decreases to about 20% by age 20 and 17% by age 80. This may be because REM sleep aids the development of the central nervous system, which includes the brain and spinal cord.

REM sleep is also associated with brain development because of the amount of time newborns spend in this stage of sleep. Newborns born with less developed brains, such as humans and puppies, spend more time in REM sleep during infancy than those born with more developed brains, like horses and birds.

During REM sleep, the brain prunes its synapses, the spaces in which brain cells communicate with one another. This improves memory and problem-solving abilities.

Wakefulness preparation

REM sleep is important for wakefulness preparation. As the night progresses, we spend an increasing amount of time in REM sleep, and it is easier to wake up during this stage. This may be because REM sleep helps us prepare to wake up by activating our central nervous system.

REM sleep is also important for dreaming, memory, emotional processing, and healthy brain development. It is associated with more brain activity than the non-REM sleep stages, and our brain activity during REM sleep is similar to how it looks when we are awake.

During REM sleep, our eyes move rapidly behind our closed eyelids, our heart rate speeds up, our breathing becomes irregular, and we experience a temporary loss of muscle tone. Researchers initially hypothesized that the temporary paralysis was a protective measure to stop us from acting out our dreams and injuring ourselves. However, this idea is now less widely accepted, as we now know that we can experience dreams during non-REM sleep stages when our bodies are not paralyzed.

REM sleep makes up about 20-25% of our total sleep time as adults, but we need the most REM sleep as infants and children when our brains are still developing. Newborn babies spend around eight hours in REM sleep each day, and this amount gradually decreases over childhood and the teen years. By age 20, most people spend just over 20% of their total sleep time in REM sleep, and this decreases slightly to about 17% by age 80.

Brain temperature regulation

Research has shown that warm-blooded animal groups with higher body temperatures have lower amounts of REM sleep, while those with lower body temperatures have more REM sleep. For example, birds have the highest body temperature of any warm-blooded animal group at 41 degrees Celsius, and they get the least REM sleep at 0.7 hours per day. In contrast, monotremes have a body temperature of 31 degrees Celsius and get 7.5 hours of REM sleep per day.

The process of brain cooling during non-REM sleep and warming during REM sleep is not universal among all animals. For example, while pigeons exhibit similar changes in cortical temperature during non-REM and REM sleep, brain temperature does not increase during REM-like sleep in bearded dragon lizards.

REM sleep is also associated with other important functions, including memory consolidation and emotional processing.

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