The Intriguing Secrets Of Rem Sleep

Sleep is a complex and mysterious body process, and understanding the physiology and pathophysiology of sleep cycles is of clinical significance. The human body cycles through two phases of sleep: rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. REM sleep is the fourth of four stages of sleep and is characterised by relaxed muscles, quick eye movement, irregular breathing, elevated heart rate, and increased brain activity. It is also known as active sleep, desynchronized sleep, paradoxical sleep, rhombencephalic sleep, and dream sleep. REM sleep plays a role in memory consolidation, emotional processing, brain development, and dreaming.

REM sleep and dreaming

REM sleep, or rapid eye movement sleep, is the fourth and final stage of the sleep cycle. It is characterised by relaxed muscles, quick eye movement, irregular breathing, an elevated heart rate, and increased brain activity. During REM sleep, the brain's activity is similar to how it behaves when awake.

REM sleep is important for several reasons. Firstly, it is associated with dreaming. While dreams can occur during non-REM sleep, the majority of dreams take place during REM sleep and tend to be more vivid. Secondly, REM sleep plays a role in memory consolidation, with the brain processing new learnings and committing some to memory. Thirdly, REM sleep is involved in emotional processing, with the amygdala (the part of the brain responsible for emotions) activating during this stage. Finally, REM sleep is thought to contribute to brain development, particularly in newborns, who spend most of their sleep time in this stage.

During a full night's sleep, humans typically cycle through the four stages of sleep multiple times, with each cycle lasting between 90 and 120 minutes. The first cycle of REM sleep usually occurs about 60 to 90 minutes after falling asleep. The first period of REM sleep is the shortest, lasting around 10 minutes, while subsequent REM stages get longer, with the final one lasting up to an hour.

While REM sleep is important for overall health and well-being, it is not the only necessary stage of sleep. Non-REM sleep, which precedes REM sleep, is when the body repairs and regrows tissues, builds bone and muscle, and strengthens the immune system. Therefore, adequate sleep should include a balance of both REM and non-REM sleep.

REM sleep and memory

REM sleep is the fourth and final stage of the sleep cycle, characterised by relaxed muscles, quick eye movement, irregular breathing, an elevated heart rate, and increased brain activity.

REM sleep is important for memory consolidation, a process that stabilises recently acquired information into long-term storage. During REM sleep, the brain repairs itself and processes emotional experiences, transferring short-term memories into long-term memories.

Memory consolidation is thought to be optimised during sleep, and while non-rapid-eye movement (NREM) sleep is directly involved in this process, the role of REM sleep has been less clear due to the difficulty in isolating neural activity during this stage. However, recent studies using a combination of electrophysiological recording and optogenetic techniques have demonstrated that neural activity during REM sleep is required for spatial and contextual memory consolidation in mice.

The amount of REM sleep needed varies across the lifespan, with newborns requiring up to eight hours of REM sleep per day, while adults need around two hours. If REM sleep is insufficient, individuals may experience symptoms such as trouble coping with emotions, concentrating, and a weakened immune system.

REM sleep and brain development

REM sleep is important for brain development, especially in early childhood. During this time, the brain is rapidly developing and REM sleep plays a role in this process.

REM sleep is characterised by relaxed muscles, quick eye movement, irregular breathing, an elevated heart rate, and increased brain activity. It is also known as "active sleep", and is associated with dreaming.

REM sleep is thought to play a role in brain development by stimulating the areas of the brain that help with learning and memory. During this stage, the brain repairs itself and processes emotional experiences, as well as transferring short-term memories into long-term memories.

Research has shown that REM sleep selectively prunes and maintains new synapses in development and learning. This process is critical for normal neuronal circuit development and behavioural improvement after learning.

REM sleep also seems to provide the stimulation needed for the preliminary development and survival of sensorimotor neuronal networks. Twitching during REM sleep is produced by the red nucleus of the brainstem, and it provides sensory feedback that activates the cells in the sensorimotor network. This activation during early REM sleep takes the form of synchronised neural oscillations that stimulate the sensorimotor cortices and distant structures, such as the brainstem and hippocampus.

Overall, REM sleep is vital for brain development, particularly in the early years of life when the brain is undergoing dramatic developmental changes.

REM sleep and emotional processing

REM sleep is critical for processing distressing emotions. It is thought that one function of sleep is to resolve emotional distress via reactivation and reorganization of neuronal circuits that were activated during the emotional experience. Animal studies have shown that reactivation may occur in the transition period from slow-wave sleep to REM sleep, while memory transformation may occur during REM sleep.

REM sleep is associated with the consolidation of emotional memories. The prefrontal cortex integrates many of these emotions during wakefulness but appears quiescent during REM sleep.

REM sleep is particularly important for emotional processing, including emotional reactivity and the formation of emotional memories. REM-sleep dreaming was also found to attenuate residual emotional load from the day before.

REM sleep deprivation has been shown to negatively impact emotional reactivity and social function. Without enough healthy sleep, negative emotional reactivity seems to be significantly enhanced and positive reactions to positive events are often subdued.

REM sleep deprivation can impede emotion regulation capacities.

REM sleep is associated with a somatodendritic decoupling in pyramidal neurons of the prefrontal cortex. This decoupling reflects a shift of inhibitory balance between parvalbumin neuron-mediated somatic inhibition and vasoactive intestinal peptide-mediated dendritic disinhibition, mostly driven by neurons from the central medial thalamus.

REM sleep deprivation may increase general negative affect.

REM sleep deprivation increases amygdala responses and alters its functional connectivity with the anterior cingulate cortex during passively experienced experimental social exclusion.

REM sleep deprivation may increase neural responses to aversive social situations.

REM sleep and physical health

REM sleep is important for physical health in several ways. Firstly, it plays a role in memory consolidation, with the brain processing new learnings and committing some to memory during this stage. A lack of REM sleep can lead to forgetfulness or poor memory. Secondly, REM sleep is associated with emotional processing, which may help with mood regulation. Thirdly, REM sleep is involved in brain development, particularly in infants and children whose brains are still developing. Newborns spend about half their sleep time in REM sleep, which gradually decreases as they grow older.

Additionally, REM sleep may offer protection against dementia. Studies suggest that people who get less REM sleep have an increased risk of developing dementia. Finally, while not directly related to physical health, the dreams that occur during REM sleep can have an impact on our emotional processing and mental health.

Frequently asked questions