Switching Sleep: Eye Movement In Rem And Non-Rem Stages

Rapid eye movement (REM) sleep is a unique phase of sleep in humans and other mammals, as well as birds, characterised by random rapid movement of the eyes, low muscle tone, and vivid dreams. During REM sleep, the body and brain undergo several changes, including rapid eye movements, increased brain activity, and a state of temporary paralysis known as atonia. The transition to REM sleep is marked by electrical bursts called ponto-geniculo-occipital waves (PGO waves) originating in the brain stem.

REM sleep is preceded by non-REM (NREM) sleep, which is further divided into four stages. As the sleep cycle repeats, REM sleep occurs several times, accounting for approximately 20-25% of an adult's sleep cycle and over 50% of an infant's.

The function of REM sleep remains a subject of ongoing research. It has been linked to memory consolidation, learning, and mood regulation. Disruptions in REM sleep have been associated with an increased risk of obesity and migraines.

REM sleep is characterised by rapid eye movements, brain activity similar to waking levels, and muscle atonia

Rapid Eye Movements

During REM sleep, the eyes move rapidly behind closed eyelids. This is where the sleep stage gets its name from. However, the eye movements are not as rapid as those exhibited by waking humans. They are also shorter in duration and more likely to loop back to their starting point. Congenitally blind people, who do not typically have visual imagery in their dreams, still move their eyes in REM sleep.

Brain Activity Similar to Waking Levels

During REM sleep, the brain acts as if it is somewhat awake, with cerebral neurons firing with the same overall intensity as in wakefulness. Brain energy use in REM sleep, as measured by oxygen and glucose metabolism, equals or exceeds energy use in waking. The rate in non-REM sleep is 11-40% lower.

Muscle Atonia

During REM sleep, the body experiences a temporary loss of muscle tone. This is thought to be a protective measure to stop sleepers from acting out their dreams and injuring themselves. However, this hypothesis is losing steam now that scientists know we can experience dreams during non-REM sleep stages when our bodies are not paralysed.

The transition to REM sleep is marked by electrical bursts called ponto-geniculo-occipital waves (PGO waves)

Ponto-geniculo-occipital (PGO) waves are phasic pontine, lateral geniculate, and cortical field potentials that occur during and before REM sleep. They are proposed to mediate a wide variety of sleep-related neural processes, including learning, brain maturation, network organisation in REM sleep, brainstem activation, and the transmission of eye movement information to the cortex.

PGO waves are characterised as biphasic, sharp field potentials lasting 60-200 ms, with an amplitude of 10-300 μV, occurring as singlets and clusters. They are generated or propagated in the pontomesencephalic tegmentum, specifically in the caudolateral peribrachial region in cats and the subcerulear region in rats.

PGO waves are closely related to REM sleep and dreaming. They are thought to be a key element of the activation-synthesis dream hypothesis, which proposes that dreams result from cortical interpretation of phasic ascending brainstem input. PGO waves are also associated with memory consolidation, specifically the preservation of procedural, spatial, and emotional memory.

PGO waves are also implicated in the unlearning theory of dreaming, which proposes that dreams serve to remove certain undesirable memories from the cerebral cortex. They may also play a role in brain development and plasticity, as well as mood regulation.

The core body and brain temperatures increase during REM sleep

During REM sleep, the core body and brain temperatures increase, while the skin temperature decreases. This is due to the loss of thermoregulation during REM sleep, which is a unique phase of sleep in mammals and birds, characterised by random rapid eye movement, low muscle tone, and vivid dreams.

The transition to REM sleep brings about marked physical changes, including electrical bursts known as "ponto-geniculo-occipital waves" (PGO waves) originating in the brain stem. The brain stem is also where the electrical and chemical activity regulating this phase seems to originate, with an abundance of the neurotransmitter acetylcholine and a near absence of monoamine neurotransmitters such as histamine, serotonin, and norepinephrine.

The increase in core body and brain temperatures during REM sleep is part of the larger circadian rhythm, which influences sleepiness and physiological factors. Body temperature starts to fall as bedtime approaches, facilitating sleep. During the night, the body temperature rises again towards morning, preparing the body for wakefulness.

The increase in brain temperature during REM sleep may be linked to the brain's increased energy use during this phase, which equals or exceeds that of a waking brain.

REM sleep is associated with dreaming and vivid dreams typically occur during this stage

REM sleep is associated with dreaming, and vivid dreams typically occur during this stage. This is due to the unique brain activity that occurs during REM sleep, which is characterised by rapid eye movements, low muscle tone, and heightened brain activity.

REM sleep is the fourth of four stages of sleep. During REM sleep, the brain acts similarly to how it does when awake, with increased brain activity and brain waves that resemble those seen during wakefulness. This is in contrast to the other three stages of sleep, during which brain waves slow down.

The first REM cycle of sleep typically occurs about 60 to 90 minutes after falling asleep. As part of a full night's sleep, sleepers cycle through three stages of non-REM sleep, followed by one stage of REM sleep. Each cycle through all the sleep stages takes 90 to 120 minutes to complete. With each new cycle, sleepers spend increasing amounts of time in REM sleep, with most of their REM sleep taking place in the second half of the night.

During REM sleep, there is more activity in the visual, motor, emotional, and autobiographical memory regions of the brain. This increased brain activity is thought to be responsible for the vivid dreams that occur during REM sleep. While dreams can also occur during non-REM sleep, they are typically more vivid during REM sleep.

REM sleep is important for several reasons beyond just dreaming. It plays a role in memory consolidation, emotional processing, and brain development. Research has also suggested that REM sleep can affect how accurately people can read emotions and process external stimuli.

In addition, the quality of REM sleep may be important for how the brain reacts to scary or stressful situations. One study found that people who spent more time in REM sleep had lower fear-related brain activity when given mild electric shocks the next day. This suggests that getting sufficient REM sleep may make a person less prone to developing post-traumatic stress disorder.

While the precise function of REM sleep is not yet fully understood, several theories have been proposed. One theory, known as the REM calibration hypothesis, suggests that norepinephrine, a neurotransmitter associated with stress, builds up during the day and can be reset to normal levels during REM sleep. This may lead to a reduced sensitivity to stimuli in the amygdala, the fear centre of the brain, and a decreased likelihood of overreacting to non-threatening stimuli.

Another theory, the activation-synthesis hypothesis, proposes that REM sleep involves pathways of "REM-on" and "REM-off" neurons in the brainstem. REM-on neurons stimulate REM-off neurons, creating a cyclical inverse relationship that regulates the transition between REM and non-REM sleep.

Overall, REM sleep is a crucial phase of sleep that is associated with vivid dreaming and plays an important role in various cognitive and emotional processes.

A lack of REM sleep may have adverse implications for physical and mental health

A lack of REM sleep can have adverse effects on both physical and mental health.

Physical Health

A lack of REM sleep can increase the risk of cardiovascular disease, including hypertension, heart attacks, and stroke. It can also contribute to obesity, type 2 diabetes, and even cancer.

Mental Health

A lack of REM sleep can cause fatigue, irritability, changes in mood and memory, and issues with cognition and problem-solving. It can also increase the risk of depression and anxiety.

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