Herbie Murray
Sleep is essential for the human body to rest, repair, and restore itself. Lack of sleep can lead to various health issues, including slowed reflexes, trouble concentrating, mood changes, a weakened immune system, and an increased risk of developing Type 2 diabetes. Sleep consists of different stages, including rapid-eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. REM sleep is characterised by rapid eye movement, heightened brain activity, and temporary muscle paralysis. During this stage, the brain repairs itself, processes emotions, and consolidates memories. Dreaming also typically occurs during REM sleep, with dreams becoming more vivid as the night progresses.
| Characteristics | Values |
|---|---|
| Brain activity | Resembles activity when awake |
| Eyes | Move rapidly |
| Body | Muscles become temporarily paralysed |
| Dreams | Most vivid dreams occur during REM sleep |
| Heart rate and breathing | Quickens |
| Learning and memory | Brain repairs itself and processes emotional experiences |
| Sleep duration | Makes up about 25% of total time asleep |
| First REM cycle | Typically lasts 10 minutes |
| Subsequent REM cycles | Longer than the first, up to an hour |
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What You'll Learn
Dreaming
During REM sleep, the brain is highly active, and dreams can be vivid and intense. This is because the brain activity during REM sleep stimulates areas of the brain that are involved in learning and memory. Dreams during REM sleep can be so vivid that people with narcolepsy, who tend to fall directly into REM sleep, may experience sudden losses of muscle strength as they act out their dreams. This is known as cataplexy.
The first REM sleep cycle typically occurs about 60 to 90 minutes after falling asleep and usually lasts for around 10 minutes. As the night progresses, the REM stages get longer, with the final one lasting up to an hour. The total REM sleep stage makes up about 20-25% of total sleep in adults, although this can vary from night to night.
The occurrence of dreaming during REM sleep is linked to the brain's ability to process and consolidate emotional experiences and memories. During this stage, the brain repairs itself and transfers short-term memories into long-term memories. This is essential for cognitive functions and emotional well-being, including learning, memory consolidation, and mood regulation.
While dreaming during REM sleep is common, it is important to note that dreams can also occur during non-REM sleep. However, these dreams tend to be less intense and less memorable. Overall, both REM and non-REM sleep are crucial for overall health and well-being, with each stage serving a unique purpose in the sleep cycle.
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Brain activity increases
During REM sleep, brain activity increases, resembling activity during wakefulness. This is characterised by fast, low amplitude, desynchronized neural oscillation (brainwaves). Specifically, the brain exhibits 3–10 Hz theta rhythm in the hippocampus and 40–60 Hz gamma waves in the cortex, similar to brain activity during wakefulness.
The brain's cerebral cortex, which interprets and processes short- and long-term memory, is active during REM sleep. The thalamus, which normally allows us to tune out the external world during sleep, remains active during REM sleep, sending the cortex images, sounds, and other sensations that fill our dreams. The amygdala, which processes emotions, also becomes increasingly active during REM sleep.
The brain's energy use during REM sleep, as measured by oxygen and glucose metabolism, is equal to or greater than its energy use when awake. Neural activity during REM sleep seems to originate in the brain stem, especially the pontine tegmentum and locus coeruleus.
REM sleep is believed to be essential for cognitive functions like memory. Dreams occur during REM sleep, and dreaming is thought to be linked to memory consolidation. However, the functional significance of dreams and REM sleep is not yet fully understood.
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Body is temporarily paralysed
During the REM sleep stage, the body experiences atonia, or temporary paralysis of the muscles, except for the eyes and the muscles that control breathing. This paralysis is called muscle atonia. It is believed that this temporary paralysis helps protect us from acting out our dreams. The brain prevents the muscles in our limbs from moving to prevent us from injuring ourselves.
Sleep paralysis occurs when you regain awareness while going into or coming out of REM sleep. During sleep paralysis, you are conscious but unable to move any part of your body. It happens when the body is between stages of sleep and wakefulness. An episode can last from a few seconds to a few minutes. It can be a frightening experience, causing intense fear and apprehension. Sleep paralysis can happen to anyone at any age and is more common among people with irregular sleep schedules.
REM sleep behaviour disorder (RBD) is a sleep disorder in which people physically act out their dreams without knowing it. They may speak or make complex movements in their sleep. RBD can be dangerous, as it can cause injury to the person or their bed partner. To receive a diagnosis of RBD, a person must undergo a sleep study that records specific body functions during sleep, such as heart rate, breathing rate, brain wave activity, eye movements, and muscle movements.
There is no treatment for sleep paralysis during an active episode. However, there are strategies to manage the underlying psychological and physical factors that trigger episodes, such as improving sleep hygiene and reducing stress.
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Eyes move rapidly
During REM sleep, the eyes move rapidly behind closed eyelids. This is one of the only visible external signs of REM sleep. The eyes move in tandem, following ponto-geniculo-occipital (PGO) waves that originate in the brain stem.
The purpose of these eye movements has been a mystery, with some researchers writing them off as random actions to keep the eyelids lubricated. However, a recent study by researchers at UC San Francisco found that the eyes move in coordination with the internal "virtual heading" of the sleeping individual. According to the study, when the eyes move during REM sleep, individuals are gazing at things in the dream world their brains have created.
The findings of the study shed light on how humans dream and how their imaginations work. The researchers monitored the eye movements of mice and compared them to the direction of their internal compass. They found that the direction of eye movements and the internal compass of the mice were precisely aligned during REM sleep, just as they are when the mice are awake and moving around.
The study also suggested that the brain's ability to combine real-world experiences with things that do not currently exist or may never exist is the basis of human creativity. This ability to create new scenarios and objects is known as the "generative brain."
While the study provides valuable insights into the relationship between eye movements and dreaming, it is important to note that the purpose of REM sleep and the function of rapid eye movements are still not fully understood.
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Memory consolidation
Sleep is essential for memory consolidation, a process that involves the reorganisation and cataloguing of memories and learned information. This process is facilitated by the brain's heightened activity during REM sleep, which resembles brain activity during wakefulness.
REM sleep is believed to be crucial for cognitive functions, including memory. Research has shown that REM sleep deprivation can lead to decreased performance on hippocampus-dependent memory tasks, particularly those requiring spatial and contextual recall. Physiological studies have also indicated that REM deprivation results in a loss of excitability in the hippocampus and a reduction in long-term potentiation, further highlighting the importance of REM sleep for memory consolidation.
During REM sleep, the brain exhibits specific neural activity patterns, such as sharp-wave ripples, slow oscillations, theta waves, and spindles, which are believed to mediate the consolidation of memories. These patterns of neural activity are observed in brain regions like the hippocampus and the prefrontal cortex, which are integral for memory formation and retrieval.
Additionally, REM sleep may play a role in the consolidation of motor learning, which does not necessarily involve the hippocampus. This suggests that REM sleep contributes to a broader range of memory functions beyond just hippocampus-dependent memories.
Furthermore, the amount of REM sleep an individual experiences can vary from night to night. Sleep deprivation or disruption can negatively impact the memory consolidation process, leading to issues with brain function and memory recall. Thus, the quantity and quality of REM sleep are essential for optimal memory consolidation.
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Frequently asked questions
REM stands for rapid eye movement. During REM sleep, your eyes move around rapidly in different directions, and your brain activity is similar to when you are awake.
During REM sleep, your brain is active and dreams occur. Your heart rate and breathing quicken, and your muscles become temporarily paralysed. This stage of sleep is important for learning and
REM sleep makes up about 20-25% of total sleep time in adults. The first REM cycle is the shortest, around 10 minutes, and each cycle that follows is longer, up to an hour.
A lack of REM sleep can lead to sleep deprivation and cause issues with brain function, memory, and emotional regulation. It can also contribute to various health problems.
