Rem Sleep: Eyes Open, Mind Dreaming

Sleep is split into two distinct states: rapid-eye-movement (REM) sleep and non-REM sleep. REM sleep is characterised by the rapid movement of the eyes, which is associated with vivid dreams. While the purpose of these eye movements has long been debated, a recent study involving mice suggests that they may reflect a shift in the animal's gaze while dreaming. This study found that the direction of eye movements and the amplitude of head movements were precisely aligned during REM sleep, just as they are when the animal is awake and moving around.

REM sleep is characterised by random rapid eye movement and is when dreams occur

Rapid eye movement (REM) sleep is a unique phase of sleep in mammals (including humans) and birds. 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.

REM sleep was first defined in 1953 by Professor Nathaniel Kleitman and his student, Eugene Aserinsky, who linked it to dreams. However, the purpose of the rapid eye movements during this sleep phase has been the subject of much debate and mystery. While some researchers have hypothesised that these eye movements follow the dream's visual scenes, others have dismissed them as random actions, perhaps serving to keep the eyelids lubricated.

A 2022 study by researchers at the University of California, San Francisco, sheds new light on the mystery. The study, which involved examining brain activity in mice, suggests that eye movements during REM sleep are not random but are, in fact, coordinated with the dreamer's gaze as they explore the virtual dream world.

During REM sleep, the eyes move rapidly from side to side, and this phase of sleep is associated with vivid dreams and increased brain activity. It accounts for 20-25% of the total sleep period in adult humans, with the first REM episode occurring about 70 minutes after falling asleep.

While REM sleep is generally characterised by closed eyes, some individuals experience nocturnal lagophthalmos, a condition where they sleep with their eyes partially or fully open. This can be caused by various factors, including faulty eyelid mechanics, facial nerve disorders, and structural changes in the face.

During REM sleep, the body is in a state of paralysis, but the brain acts as if it is awake

The transition to REM sleep brings about distinct physical changes, including electrical bursts known as ponto-geniculo-occipital (PGO) waves, which originate in the brain stem. These PGO waves are responsible for the rapid eye movements observed during REM sleep. While the purpose of these eye movements has been a subject of debate, recent studies using advanced technology have shed light on their function. Researchers at the University of California, San Francisco, found that eye movements during REM sleep are coordinated with the content of dreams. By studying mice, they discovered that the direction of eye movements aligned with the virtual dream world of the mouse, suggesting that these movements reflect shifts in gaze as the animal explores its dream environment.

The brain's electrical activity during REM sleep differs from that of non-REM sleep, with faster, low-amplitude, desynchronized neural oscillations resembling wakefulness patterns. This similarity in brain activity between REM sleep and wakefulness contributes to the characterisation of REM sleep as "paradoxical sleep." The brain's increased activity during REM sleep is also reflected in energy consumption, with brain energy use equalling or exceeding that of wakefulness.

REM sleep is not only characterised by eye movements but also by low muscle tone throughout the body. This muscle paralysis, known as REM atonia, is achieved through the inhibition of motor neurons. Hyperpolarisation occurs, further decreasing the membrane potential of motor neurons and raising the threshold for stimulation. While some twitching and reflexes can still occur during REM sleep, the body remains largely paralysed.

The state of paralysis during REM sleep serves an important purpose. Without this paralysis, individuals might act out their dreams, which could be dangerous. In fact, a condition known as REM behaviour disorder exists, where people physically act out their dreams due to a lack of REM atonia. This disorder highlights the protective role of muscle paralysis during REM sleep, ensuring the safety of the individual and those around them.

The eyes of those born blind still move during REM sleep

Rapid eye movement (REM) sleep is a unique phase of sleep in mammals (including humans) and birds, characterised by random rapid movement of the eyes, low muscle tone throughout the body, and the propensity of the sleeper to dream vividly. The eyes of those born blind still move during REM sleep, despite the absence of visual imagery in their dreams.

REM sleep was first defined in 1953 by Professor Nathaniel Kleitman and his student, Eugene Aserinsky, who linked it to dreams. However, the purpose of the rapid eye movements during this sleep phase has been the subject of much debate. A recent study by researchers at the University of California, San Francisco, sheds new light on this mystery, suggesting that eye movements during REM sleep reflect a shift in gaze as the sleeper explores the dream world.

The study, led by UCSF researcher Massimo Scanziani, PhD, and physiology postdoctoral scholar Yuta Senzai, PhD, examined the eye movements of sleeping mice. They found that these movements were not random but were, in fact, coordinated with the virtual dream world of the mouse. This discovery provides valuable insights into the cognitive processes that occur during sleep and how our imaginations work.

The findings also support the "scanning hypothesis", which suggests that the directional properties of REM sleep are related to shifts in gaze in dream imagery. This theory is further strengthened by the observation that eye movements during REM sleep occur even in those born blind and in fetuses, who lack vision. However, it is important to note that binocular REMs are non-conjugated, meaning the two eyes do not point in the same direction at the same time and lack a fixation point.

While the exact function of REM sleep remains unclear, it is known to be physiologically different from other sleep phases, with electrical and chemical activity originating in the brain stem. This phase of sleep is associated with increased brain activity and vivid dreams, and it is estimated to account for 20-25% of the total sleep period in humans.

Nocturnal lagophthalmos is a condition where people sleep with their eyes open

Nocturnal lagophthalmos occurs when a person's eyes close normally while they are awake but not when they are asleep. It can be caused by various health conditions, such as a stroke, or by issues relating to the facial muscles, nerves, or skin around the eyelids. For example, paralysis or weakening of the orbicularis oculi muscle, which closes the eyelids, can cause nocturnal lagophthalmos. Additionally, conditions such as autoimmune diseases (e.g., Guillain-Barré syndrome) or Moebius syndrome, a rare neurological condition affecting facial and eye movement, can lead to muscle weakness or paralysis of the facial nerves.

Trauma, injury, or surgery to the eye can also result in damage and paralysis to the facial muscles and nerves, causing this condition. In some cases, infections may be a less common cause, including Hansen's disease (leprosy) or Graves' disease, which can cause the eyes to bulge or protrude, making it difficult to close the eyes. Thick eyelashes, cosmetic procedures such as eyelid-tightening surgery, and even heavy alcohol ingestion or sedatives can also contribute to nocturnal lagophthalmos.

People with nocturnal lagophthalmos may experience symptoms such as irritation, soreness, watery or discharge from the eyes, scratchiness, sensitivity to light, and a feeling as if something is in the eye or under the eyelid. The condition can lead to reduced sleep quality due to the discomfort caused by dry eyes. If left untreated for an extended period, it may result in a higher risk of serious eye damage, including vision loss.

Treatment options for nocturnal lagophthalmos include medications such as artificial tears, moisture goggles or eye masks to improve eye hydration, and external eyelid weights or surgical tape to keep the eyelids closed. Lifestyle changes, such as avoiding sleeping pills and using a humidifier in the bedroom, can also help manage the condition. In severe cases, surgery may be recommended, where a gold surgical implant is inserted into the eyelid to act as a weight and keep the eye closed during sleep.

REM sleep accounts for 20-25% of total sleep

REM sleep, or rapid eye movement sleep, is a unique phase of sleep in mammals and birds, characterised by random rapid movement of the eyes. During this phase, the sleeper's brain is active and dreams typically occur. A study by researchers at the University of California, San Francisco, found that the purpose of the eye movements during REM sleep is to gaze at things in the dream world created by the brain.

REM sleep is important for learning and memory, and it helps with concentration and regulating mood. During this stage, the brain repairs itself and processes emotional experiences, transferring short-term memories into long-term memories. If an adult gets 8 hours of sleep per night, they will spend about 2 hours in REM sleep.

The amount of REM sleep needed varies across different age groups. Babies spend a lot of time in the REM stage, up to 50% of their sleep, while adults only spend about 20%. As people age, the amount of REM sleep they get decreases, but the amount of sleep they need remains the same.

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