Muscle Movement During Rem Sleep: Is It Possible?

During the REM sleep phase, the body experiences temporary paralysis of most muscles, excluding those that aid breathing, digestion, and some eye movements. This paralysis, known as REM atonia, is caused by two powerful brain chemical systems that work together to paralyse skeletal muscles. However, some muscle twitching can still occur during this phase.

Muscle twitches during REM sleep

During REM sleep, the body experiences temporary paralysis of most of the body's muscles, a state known as REM atonia. This paralysis involves most skeletal muscles but excludes muscles that help with breathing, digestion, and some eye movements.

However, muscle twitches can still occur during REM sleep. A study by Luigi De Gennaro, Michele Ferrara, and Mario Bertini found that muscle twitch frequency decreased during sleep deprivation recovery nights compared to baseline nights. Another study by Ana Paula Rivera-García et al. found that facial muscle contractions were more frequent during REM sleep, suggesting a correlation between limbic activation during REM sleep and the enhancement of facial muscle activity.

The exact mechanism behind muscle twitches during REM sleep is not yet fully understood, but research suggests that it involves the neurotransmitters gamma-aminobutyric acid (GABA) and glycine. By "switching off" the specialized cells in the brain that allow muscles to be active, these neurotransmitters can cause REM sleep paralysis.

REM sleep and muscle paralysis

During REM sleep, the body experiences muscle atonia, or REM sleep paralysis, a state of almost complete paralysis. This is considered a normal function of REM sleep. Dreaming occurs during REM sleep, and the paralysis prevents sleepers from acting out their dreams and causing harm to themselves or others.

The brain prevents the muscles in the limbs from moving during REM sleep, but some localized twitching and reflexes can still occur. For example, facial muscle contractions are a commonly observed feature during sleep stages in human subjects. A study found a significant increase in the frequency and duration of these contractions during REM sleep.

REM sleep behaviour disorder occurs when the body maintains relatively increased muscle tone during REM sleep, allowing the sleeper to move and act out their dreams. This can range from minor movements like leg twitches to very complex behaviour that may cause serious injury.

Sleep paralysis is different from REM sleep paralysis as it occurs when someone is stuck between sleep phases, either falling asleep or waking up. During sleep paralysis, a person is aware of their surroundings but cannot move or speak.

REM sleep behaviour disorder

RBD is usually seen in middle-aged to elderly people and more often in men. The exact cause of RBD is unknown, but it has been linked to degenerative neurological conditions such as Parkinson's disease, multisystem atrophy, and diffuse Lewy body dementia. It has also been associated with antidepressant use, narcolepsy, and traumatic brain injury.

The diagnosis of RBD requires confirmation through an in-laboratory sleep study (polysomnography) with video recording, which helps identify abnormal behaviours during REM sleep and excludes other sleep disorders. Treatment focuses on injury prevention and addressing any underlying conditions, as well as pharmacological interventions for severe cases, including medications such as melatonin or clonazepam.

The role of neurotransmitters in muscle paralysis during REM sleep

During REM sleep, the body is in a state of muscle paralysis, known as REM atonia. This paralysis is caused by the inhibition of motor neurons, which prevents muscle movement. The transition to REM sleep brings about marked physical changes, including the loss of muscle tone.

Neurotransmitters Involved in REM Sleep

The neurotransmitter acetylcholine is abundant during REM sleep, while monoamine neurotransmitters such as histamine, serotonin, and norepinephrine are almost completely absent.

Role of Neurotransmitters in Muscle Paralysis During REM Sleep

REM sleep paralysis is initiated when glutamatergic neurons in the subcoeruleus nucleus (SubC) activate neurons in the ventral medial medulla, leading to the release of GABA and glycine onto skeletal motor neurons. This results in the inhibition of skeletal motor neurons, causing muscle paralysis.

In addition to the role of the SubC, the dorsal paragigantocellular reticular nucleus (DPGi), a group of GABA-containing neurons, may also play a role in REM sleep initiation by inhibiting wake-promoting areas of the brain.

The interaction of various neurotransmitter systems in the brainstem, forebrain, and hypothalamus is essential for the initiation and maintenance of REM sleep and its characteristic muscle paralysis. Understanding the role of these neurotransmitters is crucial for developing treatments for sleep disorders related to REM sleep, such as narcolepsy and REM sleep behavior disorder.

REM sleep and memory

Muscle movement can occur during REM sleep, but it is limited. The body abruptly loses muscle tone during REM sleep, a state known as REM atonia. This is accomplished through the inhibition of motor neurons. However, some localized twitching and reflexes can still occur.

The relationship between REM sleep and memory has been studied across various species, including humans, rats, and mice. Research suggests that REM sleep may favor the preservation of certain types of memories, such as procedural memory, spatial memory, and emotional memory. For example, in rats, REM sleep increases following intensive learning, and deprivation of REM sleep has been shown to inhibit memory consolidation, particularly for complex tasks.

In humans, the strongest evidence for the role of REM sleep in memory pertains to the learning of new physical movements and problem-solving techniques. REM sleep deprivation appears to impair declarative memory, but only for more complex information, such as longer stories. Additionally, REM sleep seems to counteract attempts to suppress certain thoughts.

The dual-process hypothesis suggests that the two major phases of sleep, REM and NREM, correspond to different types of memory. Slow-wave sleep, part of NREM sleep, is important for declarative memory, while REM sleep may be more crucial for procedural memory.

Overall, while the precise function of REM sleep remains unclear, it plays a significant role in memory consolidation, particularly for certain types of memories.

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