What Happens To Your Body During Rem Sleep?

Sleep is a complex and dynamic process that affects our functioning in ways scientists are only beginning to understand. During sleep, our bodies cycle between being awake and asleep, with certain processes only happening when we are asleep. One of these processes is REM sleep, which stands for rapid eye movement sleep. During REM sleep, our eyes move rapidly, our brain activity increases, and we experience an increase in heart rate, blood pressure, and breathing. Our muscles also become temporarily paralysed, preventing us from acting out our dreams. REM sleep is important for brain health and function, including learning, memory, emotional processing, and brain development. While the exact amount of REM sleep needed varies across individuals, most adults require around two hours of REM sleep per night.

Dreaming and memory consolidation

The process of memory reactivation and consolidation in the sleeping brain appears to influence conscious experience during sleep, contributing to dream content recalled on awakening. It is increasingly clear that sleep facilitates the consolidation of memory. A large number of studies have now replicated the robust finding that sleep following learning improves memory performance at a subsequent test. Recent discoveries in the neuroscience of learning and memory have been particularly enlightening in thinking about just how memory might be facilitated during sleep.

Groundbreaking research in the last two decades has established the remarkable fact that waking patterns of brain activity are "replayed" during sleep in rodents. For example, sequences of hippocampal place cell activity seen while rats explore a spatial environment during wakefulness are again observed when the rats fall asleep. As the firing of each of these hippocampal "place" cells is associated with a particular physical location in the environment, the reappearance of these sequences suggests that during sleep, rats are retracing the paths they have learned.

The discovery of memory reactivation during sleep certainly suggests a parallel with dreams of recent experience. Perhaps rats are dreaming of the "maze" they traversed while awake. Of course, we know that not all brain activity is consciously experienced. The neural activity associated with the regulation of respiration and heart rate, for example, does not influence our stream of conscious awareness. Analogously, these cellular firing sequences in small regions of rodent hippocampus and cortex may be irrelevant to understanding the stream of consciousness during sleep.

However, is this so-called memory "replay" during sleep at least a good potential candidate for a neural correlate of dreaming? A complete review of the memory reactivation literature is beyond the scope of this article, but it is noteworthy that several key features of this phenomenon parallel the structure of dream experience:

• In rodent studies, memory reactivation has most often been reported to occur in non-rapid eye movement (NREM) sleep. As described earlier, NREM sleep is also the sleep stage during which episodic memories are most often incorporated into dreaming.
• Within NREM sleep, reactivation is expressed most strongly immediately after learning. The strength of this reactivation effect then tends to decay quickly across time. Similarly, sleep mentation may be most strongly related to recent experience early in the sleep phase.
• Learning-related neural activity is not reactivated exactly in its original form. Waking firing sequences are reactivated in intermittent bursts, on a faster timescale than the original experience. And rarely is a waking firing sequence reiterated exactly—although reactivated sequences statistically resemble waking activity, the "replay" is not always precise. Similarly, recent experiences are not "replayed" in dream content in their original form. Instead, dreams intermingle fragments of recent experience with other content.

Brain activity and body paralysis

Sleep paralysis is a condition in which a person is unable to move or speak right before falling asleep or immediately after waking up. During an episode of sleep paralysis, the person is fully aware of their surroundings but is unable to move or speak. Sleep paralysis occurs when the sleep cycle is shifting between stages. When a person wakes up suddenly from REM sleep, their brain is awake, but their body is still in REM mode and cannot move.

During REM sleep, the eyes move rapidly behind closed eyelids, the heart rate speeds up, and breathing becomes irregular. The brain is highly active during REM sleep, and brain waves become more variable. The body operates similarly to how it does when a person is awake, except for the eyes being closed and a temporary loss of muscle tone. The loss of muscle tone or temporary paralysis during REM sleep is thought to be a protective measure to stop people from acting out their dreams and causing injury to themselves.

Sleep paralysis can be caused by various factors, including sleep deprivation, irregular sleep schedules, and certain medical conditions. It is not typically dangerous but can cause emotional distress. While there is no treatment to stop an episode of sleep paralysis, certain medications and therapies can help reduce its frequency.

During REM sleep, the brain exhibits increased activity compared to non-REM sleep, with brain waves similar to those seen during wakefulness. The pons, thalamus, limbic areas, and temporo-occipital cortices are activated during REM sleep, while prefrontal areas show decreased activity. This activation pattern aligns with theories of REM sleep generation and the occurrence of dreams.

The increased brain activity during REM sleep is crucial for several cognitive functions, including dreaming, memory consolidation, emotional processing, and brain development. Most adults need about two hours of REM sleep each night for optimal cognitive performance. Deprivation of REM sleep can interfere with memory formation and disrupt the brain's ability to generate new cells.

Emotional processing and mental health

Emotional processing during REM sleep is thought to be important for the processing and consolidation of emotional memories, including fear memories. Rhythmic interactions, especially in the theta band, between the medial prefrontal cortex (mPFC) and limbic structures are thought to play an important role, but the ways in which memory processing occurs at a mechanistic and circuits level are largely unknown. To investigate how rhythmic interactions lead to fear extinction during REM sleep, we used a biophysically based model that included the infralimbic cortex (IL), a part of the mPFC with a critical role in suppressing fear memories. Theta frequency (4–12 Hz) inputs to a given cell assembly in IL, representing an emotional memory, resulted in the strengthening of connections from the IL to the amygdala and the weakening of connections from the amygdala to the IL, resulting in the suppression of the activity of fear expression cells for the associated memory. Lower frequency (4 Hz) theta inputs effected these changes over a wider range of input strengths. In contrast, inputs at other frequencies were ineffective at causing these synaptic changes and did not suppress fear memories. Under post-traumatic stress disorder (PTSD) REM sleep conditions, rhythmic activity dissipated, and 4 Hz theta inputs to IL were ineffective, but higher-frequency (10 Hz) theta inputs to IL induced changes similar to those seen with 4 Hz inputs under normal REM sleep conditions, resulting in the suppression of fear expression cells. These results suggest why PTSD patients may repeatedly experience the same emotionally charged dreams and suggest potential neuromodulatory therapies for the amelioration of PTSD symptoms.

Sleep disorders and health risks

Sleep is a basic human need, critical to both physical and mental health. Sleep disorders (or sleep-wake disorders) involve problems with the quality, timing, and amount of sleep, which result in daytime distress and impairment in functioning.

Sleep disorders can have a detrimental impact on overall health, including brain function and cellular repair. They can also lead to or exacerbate mental health issues such as depression, anxiety, or cognitive disorders. Sleep problems can also be a symptom of other mental health conditions.

• Insomnia: Insomnia is the most common sleep disorder, characterised by difficulties falling asleep or staying asleep. It can lead to fatigue, decreased energy, irritability, and problems with focus and concentration. Chronic insomnia can disrupt brain function and is often associated with mental health conditions.
• Obstructive Sleep Apnea: This disorder involves breathing interruptions during sleep, causing snoring, gasping, or breathing pauses. It results in poor sleep quality and can increase the risk of respiratory infections and cardiovascular disease.
• Restless Leg Syndrome: An urge to move the legs, often accompanied by uncomfortable sensations, can make it difficult to fall asleep and cause daytime sleepiness.
• Circadian Rhythm Sleep-Wake Disorders: In these disorders, an individual's sleep-wake cycles become misaligned with the external light-darkness cycle, leading to significant sleep problems and daytime sleepiness.
• REM Sleep Behavior Disorder: During REM sleep, people with this disorder may act out their dreams, shouting, punching, or kicking. This can lead to injuries and social isolation.
• Narcolepsy: People with narcolepsy experience sudden sleep episodes during the day and may also have cataplexy, a sudden loss of muscle tone.
• Nightmare Disorder: Regular and distressing nightmares are associated with this disorder, often caused by stress, childhood trauma, or other frightening experiences.

Treating sleep disorders is essential for maintaining overall health and well-being. Treatments can vary and may include medications, devices, or behavioural techniques such as cognitive-behavioural therapy.

Improving sleep quality

• Set a sleep schedule: Try to go to bed and wake up at the same time every day, even on weekends. This helps your body get accustomed to a healthy sleep routine.
• Create a bedtime routine: Engage in relaxing activities such as quiet reading, low-impact stretching, listening to soothing music, or relaxation exercises about 30 minutes before bedtime. This helps signal to your brain that sleep is approaching.
• Avoid bright lights and electronics before bed: The blue light emitted by electronic devices can disrupt your natural melatonin production. Disconnect from devices at least an hour before bedtime, and avoid bright lights.
• Get natural light exposure during the day: Sunlight exposure helps regulate your body's internal clock and improve sleep quality. If natural light is not accessible, consider using a light therapy box.
• Exercise regularly: Daily exercise improves overall health and sleep quality. However, avoid intense exercise close to bedtime as it may hinder your ability to relax before sleep.
• Limit caffeine and alcohol intake: Caffeine and alcohol can disrupt sleep. Avoid consuming caffeinated beverages at least eight hours before bedtime, and refrain from alcohol in the hour leading up to bedtime.
• Optimize your bedroom environment: Maintain a cool, dark, and quiet bedroom. Invest in blackout curtains or a sleep mask to block out light, and use earplugs or a white noise machine to minimize noise.
• Get comfortable bedding: Ensure your mattress, pillow, and bedding are comfortable and supportive. This helps you relax and prevents aches and pains.
• Avoid heavy meals and liquids before bed: Eating a large meal or drinking excessive liquids before bed can disrupt your sleep due to digestion and frequent urination. Finish dinner a few hours before bedtime, and opt for a light snack if needed.
• Practice relaxation techniques: Mindfulness, meditation, deep breathing, and visualization are techniques that can improve sleep quality and are commonly used to treat insomnia.

Frequently asked questions