Signs Of Rem Sleep: Behavioral And Physiological Changes

REM sleep is the fourth out of four stages of sleep. It is characterised by relaxed muscles, quick eye movement, irregular breathing, an elevated heart rate, and increased brain activity. This stage of sleep is also known as active sleep, desynchronized sleep, paradoxical sleep, rhombencephalic sleep, and dream sleep. While it is true that most dreams occur during REM sleep, it is a common misconception that it is the only stage in which dreams occur.

Rapid eye movement

REM sleep occurs after the brain passes through the three stages of NREM sleep, typically about 90 minutes after falling asleep. The first REM cycle is the shortest, lasting about 10 minutes, and each subsequent cycle gets longer, with the final one lasting up to an hour. During the initial cycle, the REM period may last only 1 to 5 minutes, but it becomes progressively longer as the sleep episode progresses.

REM sleep is a much deeper sleep than any of the three stages of NREM sleep. It is characterised by rapid eye movements and an almost complete paralysis of the body, known as REM atonia, where motor neurons are completely inhibited. In this stage, brain waves are fast and low in amplitude, similar to the pattern seen during wakefulness. Dreaming mostly occurs during REM sleep, and studies have shown that dreams recalled after being awakened from REM sleep are more elaborate, vivid, and emotional than dreams recalled after NREM sleep.

REM sleep makes up about 20 to 25% of total sleep time in adults, but the percentage is much higher in babies, at up to 50%. As people age, the percentage of REM sleep declines rapidly so that by approximately age 10, the adult percentage is reached. However, REM rebound, or an increase in REM sleep above normal levels, can occur after a period of sleep deprivation.

Increased heart rate

During REM sleep, the body experiences an increase in heart rate. This is one of the physiological changes that occur during sleep, and it is primarily determined by autonomic nervous system activity. Brief increases in heart rate can occur with K-complexes (high amplitude patterns of brain activity that may occur in response to environmental stimuli), arousals, and large body movements.

The increase in heart rate during REM sleep is accompanied by a rise in sympathetic nerve activity. This means that the sympathetic nervous system, which is responsible for the body's "fight or flight" response, becomes more active during this stage of sleep. This increase in sympathetic nerve activity is in contrast to what happens during non-REM sleep, where sympathetic-nerve activity decreases as NREM sleep deepens.

The rise in heart rate during REM sleep is also associated with an increase in blood pressure. This brief increase in blood pressure can further trigger a burst of sympathetic nerve activity. The combination of increased heart rate, blood pressure, and sympathetic nerve activity during REM sleep contributes to the body's overall physiological response to this stage of sleep.

While the increase in heart rate during REM sleep is a normal part of the sleep cycle, it is important to note that it can have clinical implications. For example, there is an increased risk of myocardial infarction (heart attack) in the morning due to the sharp increases in heart rate and blood pressure that accompany awakening. Therefore, while increased heart rate is a physiological sign of REM sleep, it also has potential health consequences that should be considered.

In summary, increased heart rate during REM sleep is a result of the body's autonomic nervous system activity and is associated with changes in blood pressure and sympathetic nerve activity. This physiological response is a normal part of the sleep cycle but also highlights the complex interplay between different body systems during sleep.

Irregular breathing

During REM sleep, the respiratory pattern is characterised by brief periods of central apnea, where breathing momentarily ceases. These apneas can last from a few seconds to up to 20 seconds. The respiratory system is primarily under chemical-metabolic control during this stage, similar to non-REM sleep. However, the breathing pattern is also influenced by the behavioural system through REM sleep processes, which include ponto-geniculo-occipital (PGO) waves. These PGO waves are associated with excitatory and inhibitory influences that affect breathing.

The irregular breathing patterns observed during REM sleep may be related to the mental imagery and emotional content of dreams. Dreams that involve physical activity or intense emotions can lead to changes in respiration, such as increased ventilation or hyperventilation. Additionally, the act of dreaming itself may require cortical control of ventilation, resulting in irregular breathing patterns.

Furthermore, the loss of the wakefulness stimulus during sleep can contribute to respiratory instability. In awake individuals, the wakefulness stimulus helps maintain respiratory function even during periods of reduced chemical stimuli, such as vigorous singing or crying. However, during sleep, the loss of this stimulus can make the respiratory control system more sensitive to transient reductions in carbon dioxide levels, predisposing individuals to apnea.

In summary, irregular breathing during REM sleep is a physiological sign that may be influenced by various factors, including dream content, cortical processes, and changes in respiratory control. The erratic breathing patterns observed during this sleep stage contribute to the unique characteristics of REM sleep and play a role in the overall respiratory function during sleep.

Brain activity similar to when awake

During REM sleep, brain activity is similar to that of a waking brain. This is when dreams occur, and the brain shows increased activity and resembles an alert state.

REM sleep is defined by rapid eye movements and an almost complete paralysis of the body, otherwise known as REM atonia, where motor neurons are completely inhibited. The brainwaves during this stage are fast and low amplitude, similar to the pattern seen during wakefulness.

EEG (electroencephalography) is used to measure brainwave activity during sleep. This technology has shown that during REM sleep, the brain is highly active, with brainwaves that are fast and low in amplitude.

The first REM cycle is typically the shortest, lasting about 10 minutes, and occurring 90 minutes after falling asleep. Each subsequent cycle gets longer, with the final one lasting up to an hour.

The brain activity during REM sleep is so similar to wakefulness that people can sometimes act out their dreams, a condition known as REM Sleep Behavior Disorder (RBD). People with RBD may speak or perform complex movements in their sleep and are at risk of injuring themselves or their bed partner.

Dreaming

Dreams are believed to play a role in memory consolidation and emotional processing. This idea suggests that dreams help us make sense of our daily experiences, sort through our emotions, and store important memories. This theory is supported by the observation that brain activity during REM sleep resembles that of wakefulness, indicating a possible connection to memory and emotional processing.

Dreams may also serve as a form of threat simulation or preparation for potential dangers. This theory, known as the "threat simulation theory," proposes that dreams allow us to rehearse threatening situations in a safe environment, improving our ability to respond to real-life threats.

Additionally, dreams have been linked to the development of cognitive capabilities and the reflection of unconscious mental processes. Some researchers suggest that dreams facilitate the further development of our cognitive abilities, while others explore the idea that dreams provide a window into our unconscious thoughts and feelings.

The content and nature of dreams can vary widely, and they often involve vivid imagery, emotions, and sensations. While some dreams may be pleasant, others can be frightening or disturbing. The emotional intensity of dreams is particularly notable during REM sleep, where they tend to be more elaborate and memorable.

It is worth noting that the study of dreams and their significance is a complex and ongoing area of research. While these theories provide insight, there is still much to discover about the purpose and function of dreams.

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