Understanding Rem Paralysis: Why Muscles Freeze During Sleep

During the REM sleep phase, the brain inhibits the motor system, causing muscle paralysis or muscle atonia. This paralysis is considered a normal function of REM sleep, preventing the body from acting out dreams and causing potential injury. While the exact cause of this paralysis was previously unknown, recent research has identified two powerful brain chemical systems that work together to paralyze skeletal muscles during REM sleep. Understanding the mechanisms behind this paralysis is important for treating sleep disorders such as REM Behavior Disorder, where people act out their dreams due to the absence of paralysis, and sleep paralysis, where people experience temporary immobility before falling asleep or upon waking up.

Brain chemicals GABA and glycine cause muscle paralysis

During REM sleep, the brain inhibits the motor system, which makes the sleeper completely immobile. This is called REM sleep muscle paralysis or muscle atonia. Two powerful brain chemical systems work together to paralyze skeletal muscles during REM sleep. These are the neurotransmitters gamma-aminobutyric acid (GABA) and glycine.

In 2012, University of Toronto neuroscientists Patricia L. Brooks and John H. Peever, PhD, found that GABA and glycine caused REM sleep paralysis in rats by "switching off" the specialized cells in the brain that allow muscles to be active. This finding reversed earlier beliefs that glycine was the lone inhibitor of these motor neurons. The researchers measured electrical activity in the facial muscles responsible for chewing in sleeping rats. They found that to prevent REM sleep paralysis, they had to block both the ionotropic receptors and metabotropic GABAB receptors. In other words, when the motor cells were cut off from all sources of GABA and glycine, the paralysis did not occur, allowing the rats to exhibit high levels of muscle activity when their muscles should have been inactive.

The data suggest that the two neurotransmitters must both be present together to maintain motor control during sleep, rather than working separately. This finding could be especially helpful for those with REM sleep disorder, a disease that causes people to act out their dreams. This can cause serious injuries to patients and others around them. It is also often an early indicator of neurodegenerative diseases, such as Parkinson's.

Preventing injury from acting out dreams

During the REM sleep phase, muscles are typically at rest, and the body is paralysed. However, in some cases, people with REM sleep behaviour disorder (RBD) act out their dreams, which can cause injury to themselves or their bed partner. This is often an early indicator of neurodegenerative diseases, such as Parkinson's.

To prevent injury from acting out dreams, it is important to address the underlying cause of RBD. While the exact cause of RBD is unknown, it has been linked to certain factors, including:

• Age: RBD usually appears around the age of 50.
• Neurological disorders: RBD has been associated with neurological disorders such as Parkinson's disease.
• Adverse drug reactions: Adverse reactions to certain drugs or drug withdrawal can sometimes appear as RBD.
• Sleep disorders: Treating coexisting sleep disorders is important in managing RBD.
• Medication changes: Medications are often changed or started to reduce symptoms of RBD.

In addition to addressing these underlying factors, the following precautions can be taken to prevent injury:

• Ensure a safe sleep environment: Remove any hazardous objects or obstacles from the bedroom to reduce the risk of injury if the person does act out their dreams.
• Improve sleep hygiene: Establish a consistent sleep schedule, create a comfortable and relaxing sleep environment, and avoid electronic devices before bed to improve sleep quality and reduce the risk of sleep deprivation, which can contribute to RBD.
• Treat mental health conditions: RBD has been associated with mental health conditions such as anxiety, bipolar disorder, and post-traumatic stress disorder (PTSD). Seeking treatment for these conditions may help reduce the severity or frequency of RBD.
• Medications: Clonazepam, an antipsychotic drug, is currently used to treat RBD.

Neurons are responsible for muscle paralysis

During the REM sleep phase, the brain inhibits the motor system, making the body immobile. This is called REM sleep muscle paralysis or muscle atonia. It is considered a normal function of REM sleep, which is the deep sleep phase where most recalled dreams occur. During REM sleep, the brain is very active, and dreams are at their most intense. However, the voluntary muscles of the body, including the arms, legs, fingers, and other muscles under conscious control, are paralyzed.

Neurons are responsible for this muscle paralysis. Research by neuroscientists at the University of Toronto found that the neurotransmitters gamma-aminobutyric acid (GABA) and glycine caused REM sleep paralysis in rats by "switching off" the specialized cells in the brain that allow muscles to be active. This discovery contradicted previous beliefs that glycine was the sole inhibitor of these motor neurons. The researchers found that to induce REM sleep paralysis, they had to block both the ionotropic receptors and metabotropic GABAB receptors simultaneously. When the motor cells were cut off from all sources of GABA and glycine, paralysis did not occur, and the rats exhibited high levels of muscle activity when they should have been inactive.

The study's findings have important implications for understanding and treating sleep disorders, such as REM sleep behavior disorder, narcolepsy, and tooth grinding. By identifying the neurotransmitters involved in sleep-related paralysis, researchers can now explore possible molecular targets for developing treatments for sleep-related motor disorders.

Additionally, the identification of neurons responsible for muscle paralysis during REM sleep has significant implications for understanding and treating neurodegenerative diseases. Research has shown that patients diagnosed with REM sleep behavior disorder often develop the motor symptoms of neurodegenerative diseases like Parkinson's disease later in life. By creating animal models that mimic this disorder, scientists can gain insights into the degeneration of neurons and potentially develop interventions to prevent or slow the progression of these diseases.

REM sleep behaviour disorder

During REM sleep, the brain inhibits the motor system, which makes the sleeper completely immobile. Dreaming occurs during this sleep stage, and it is usually associated with rapid eye movement, even breathing, blood pressure rises, and muscle paralysis. However, in the case of REM Sleep Behaviour Disorder, the paralysis that normally occurs during REM sleep is incomplete or absent, allowing the person to act out their dreams. This can include minor movements like leg twitches, but can also result in very complex and violent behaviour that may cause serious injury to the individual or their bed partner.

The cause of REM Sleep Behaviour Disorder is not always known, but it has been linked to certain factors. In some cases, it may be caused by adverse reactions to certain drugs, such as antidepressants, or drug withdrawal. It is also more common with age and has been associated with neurological disorders, particularly neurodegenerative diseases like Parkinson's disease. Research has shown that people diagnosed with REM Sleep Behaviour Disorder often go on to develop neurodegenerative diseases, with an estimated conversion rate of 6.3% per year and a total of 74% converting after a 12-year follow-up.

The diagnosis of REM Sleep Behaviour Disorder is confirmed by a sleep study, specifically polysomnography with video recording, which helps to identify abnormal behaviours during REM sleep and exclude other sleep disorders. The primary goal of treatment is to reduce the risk of injury to the patient and their bed partner. This may involve changing routine sleep habits and taking safety precautions, such as lowering the bed or cushioning sharp furniture surfaces. Pharmacological treatments, such as melatonin or clonazepam, may also be used to reduce symptoms.

Sleep paralysis

During REM sleep, the brain is highly active, and dreams are most intense. The brain inhibits the motor system, making the sleeper completely immobile. This paralysis is caused by two powerful brain chemical systems involving the neurotransmitters gamma-aminobutyric acid (GABA) and glycine. These neurotransmitters "switch off" the specialised cells in the brain that enable muscle activity, and both must be present together to induce and maintain motor control during sleep.

The identification of these neurotransmitters is significant for understanding and treating sleep disorders such as narcolepsy, tooth grinding, and REM sleep behaviour disorder (RBD). RBD is a parasomnia where patients talk, move, kick, and even fall out of bed, reflecting their dream activity. This disorder usually appears around the age of 50 and is often an early indicator of neurodegenerative diseases, such as Parkinson's disease.

While there is no treatment to stop a sleep paralysis episode once it starts, treatments are available to reduce the frequency of episodes. These include medications to prevent reaching the REM stage of sleep or to treat underlying mental health conditions or sleep disorders. Additionally, improving sleep hygiene practices, such as maintaining a consistent sleep schedule and creating a comfortable sleep environment, can help reduce the risk of sleep paralysis.

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