Sleep is a complex and dynamic process that is essential for human survival. It is composed of several stages, primarily distinguished as REM (rapid-eye movement) sleep and non-REM sleep. During the first stage of non-REM sleep, individuals experience a transitional phase between wakefulness and sleep, marked by a slowdown in respiration and heartbeat, and the presence of alpha and theta waves. As they progress into the second stage, the body enters a state of deep relaxation, with theta waves interrupted by sleep spindles and K-complexes. The third stage of non-REM sleep is characterised by delta waves and is the deepest level of sleep, where it is most difficult to wake someone. Following this, individuals enter the REM stage, which is associated with vivid dreaming and paralysis of muscles. Brain waves during REM sleep exhibit similarities to those during wakefulness, with higher brain activity and lower muscle tone. This stage is also known as paradoxical sleep.
Characteristics | Values |
---|---|
Brain wave activity | Similar to those during wakefulness |
Eye movement | Rapid and random |
Muscle tone | Low throughout the body |
Dreaming | Vivid |
Core body and brain temperature | Increase |
Skin temperature | Decrease to lowest values |
What You'll Learn
Brain waves during REM sleep are similar to brain waves during wakefulness
Sleep is not a uniform state. Instead, it is composed of several different stages that can be differentiated from one another by the patterns of brain wave activity that occur during each stage. These changes in brain wave activity can be visualised using an electroencephalogram (EEG) and are distinguished from one another by both the frequency and amplitude of brain waves.
Sleep can be divided into two different general phases: REM sleep and non-REM (NREM) sleep. REM sleep is characterised by darting movements of the eyes under closed eyelids, and brain waves during this stage appear very similar to brain waves during wakefulness.
During REM sleep, the brain acts as if it is awake, with cerebral neurons firing with the same overall intensity as in wakefulness. Electroencephalography during REM sleep reveals fast, low amplitude, desynchronised neural oscillation (brain waves) that resemble the pattern seen during wakefulness. This differs from the slow delta waves pattern of NREM deep sleep.
The brain waves associated with REM sleep are very similar to those observed when a person is awake. This is the period of sleep in which dreaming occurs. It is also associated with the paralysis of muscle systems in the body, except for those that make circulation and respiration possible. Therefore, no movement of voluntary muscles occurs during REM sleep in a normal individual. REM sleep is often referred to as paradoxical sleep because of this combination of high brain activity and lack of muscle tone.
The superior frontal gyrus, medial frontal areas, intraparietal sulcus, and superior parietal cortex—areas involved in sophisticated mental activity—show equal activity in REM sleep as in wakefulness. The amygdala is also active during REM sleep and may participate in generating electrical bursts called "ponto-geniculo-occipital waves" (PGO waves), which originate in the brain stem and are a cause of the rapid eye movements in paradoxical sleep.
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REM sleep is characterised by random rapid movement of the eyes
Sleep is composed of several different stages, including REM sleep and non-REM sleep. REM sleep, or rapid eye movement sleep, is characterised by random rapid movement of the eyes, low muscle tone throughout the body, and the propensity of the sleeper to dream vividly. The core body and brain temperatures increase during REM sleep, while the skin temperature decreases to its lowest values.
REM sleep is physiologically different from the other phases of sleep, which are collectively referred to as non-REM sleep. The absence of visual and auditory stimulation (sensory deprivation) during REM sleep can cause hallucinations. REM sleep and non-REM sleep alternate within one sleep cycle, which lasts about 90 minutes in adult humans. As sleep cycles continue, they shift towards a higher proportion of REM sleep. The transition to REM sleep brings marked physical changes, beginning with electrical bursts called "ponto-geniculo-occipital waves" (PGO waves) originating in the brain stem.
During REM sleep, the eyes move rapidly in different directions, and the brain is active. Brain activity during REM sleep is similar to brain activity when a person is awake. Dreams typically occur during REM sleep. The first REM cycle of a sleep period is typically the shortest, around 10 minutes, with each subsequent cycle getting longer, up to an hour.
REM sleep is important for learning and memory. During this stage, the brain repairs itself and processes emotional experiences. It also transfers short-term memories into long-term memories. If a person does not get enough REM sleep, they may experience symptoms such as trouble coping with emotions, trouble concentrating, a weakened immune system, and feeling groggy in the morning.
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Dreaming occurs during REM sleep
The discovery of REM sleep and its association with dreaming was first made in the 1950s by Eugene Aserinsky, a physiology student. Aserinsky conducted an experiment on his 8-year-old son, recording his brain activity and eye movements during sleep. This experiment led to the first scientific report of REM sleep and sparked further research into the connection between REM sleep and dreaming.
While it is true that a majority of dreams occur during REM sleep, it is a common misconception that dreaming is limited to this stage of sleep. Research has shown that dreaming can also occur during the early, non-REM stages of sleep. Dreams during REM sleep tend to be more vivid, emotional, and physically engaging, making them easier to remember. However, lucid dreaming, where the dreamer is aware that they are dreaming, can occur during both REM and non-REM sleep.
The stages of non-REM sleep are characterised by slower brain waves and deeper relaxation. During the first stage of non-REM sleep, the body transitions from wakefulness to sleep, with a decrease in heart rate, breathing, and muscle tension. The second stage is marked by further slowing of heart rate and breathing, and a drop in body temperature. The third stage is deep sleep, where it becomes difficult to wake the sleeper, and the brain produces slow delta waves.
In summary, dreaming is most commonly associated with REM sleep due to the heightened brain activity and vivid nature of dreams during this stage. However, dreaming is not exclusive to REM sleep, and it can occur during other stages of sleep as well.
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REM sleep is also known as paradoxical sleep
Sleep is composed of several different stages, including REM sleep and non-REM sleep. Brain wave activity during REM sleep is characterised by high brain activity and a lack of muscle tone, resembling the brain waves of someone who is awake. This combination of high brain activity and muscle paralysis has earned REM sleep the name "paradoxical sleep".
During REM sleep, the brain waves associated with this stage of sleep are very similar to those observed when a person is awake. Brain activity speeds up and becomes similar to the activity seen during waking hours, which can lead to complex and vivid dreams. At the same time, the body falls into temporary paralysis, with many muscles becoming inactive. This is important for keeping the body still during sleep, such as preventing the legs from kicking out during a dream about running.
The paradoxical nature of REM sleep was first recognised by French researcher Michel Jouvet, who named it "paradoxical sleep" due to its waking EEG during behavioural sleep. The brain acts as if it is somewhat awake, with cerebral neurons firing with the same overall intensity as in wakefulness. This high level of brain activity during REM sleep is also reflected in brain energy use, which equals or exceeds that of a waking brain.
In addition to the name "paradoxical sleep", REM sleep is sometimes referred to as "desynchronized sleep" or "dreamy sleep", further highlighting the similarities between this sleep stage and a waking state.
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The transition to REM sleep brings about marked physical changes
During REM sleep, the brain exhibits fast, low-amplitude, desynchronized neural oscillation (brain waves) that are similar to the patterns observed during wakefulness. This is in contrast to the slow delta waves typically seen during non-REM (NREM) deep sleep. The electrical connectivity between different brain regions changes, with frontal and posterior areas showing less coherence in most frequencies, while the right and left hemispheres, as well as the posterior areas, exhibit increased coherence.
The transition to REM sleep is also marked by an increase in core body and brain temperatures, while the skin temperature decreases to its lowest values. Organisms experience a loss of muscle tone, known as REM atonia, which results in temporary paralysis of the body's voluntary muscles. This prevents individuals from acting out their dreams.
The transition to REM sleep is associated with a suspension of homeostasis, leading to large fluctuations in respiration, thermoregulation, and circulation that are not observed during other sleep or waking states. Heart rate, cardiac pressure, cardiac output, arterial pressure, and breathing rate become irregular. The brain exerts less control over respiration, and electrical stimulation of respiration-linked brain areas does not influence the lungs during REM sleep, as it does during NREM sleep and wakefulness.
The transition to REM sleep is punctuated by PGO waves, which occur in bursts about every 6 seconds for 1-2 minutes during the shift from deep sleep to REM sleep. These waves are responsible for the rapid eye movements that characterise this sleep stage, as they influence the eyes to move in tandem, following the waves' origin in the brain stem.
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Frequently asked questions
REM stands for rapid eye movement sleep. It is characterised by random rapid movement of the eyes, low muscle tone throughout the body, and the propensity of the sleeper to dream vividly. Brain waves during REM sleep are very similar to brain waves during wakefulness.
Non-REM sleep is the period of sleep outside of REM sleep. It is subdivided into three stages, each distinguished by characteristic patterns of brain waves. The first stage is a transitional phase between wakefulness and sleep, during which there is a slowdown in respiration and heartbeat. The second stage is a period of light sleep, during which the body goes into a state of deep relaxation. The third stage is deep sleep, during which it is difficult to wake the sleeper.
During REM sleep, brain waves are similar to those observed during wakefulness. In contrast, non-REM sleep is characterised by slow-wave sleep, with low-frequency, high-amplitude delta waves.
The precise function of REM sleep is not well understood. However, several theories have been proposed, including:
- The preservation of certain types of memories (procedural, spatial, and emotional)
- The removal of undesirable modes of interaction in networks of cells in the cerebral cortex
- The stimulation and stabilisation of neural circuits that have not been activated during wakefulness
- The creation of internal stimulation to aid the development of the central nervous system