Scientists have been challenged by the mystery of “Rapid eye movement sleep” (REM sleep) while studying its distinct difference from other kinds of sleep. It makes a significant part of our sleep architecture as we spend a quarter of the night in this stage (ideally). But what exactly is REM sleep?

What is rapid eye movement REM sleep?

During sleep, the brain passes through five different stages, one of which is REM. During this phase, eye movement increases rapidly in various dimensions. The other four phases come under the category of “ non-REM” sleep.

It is one of the four stages of sleep. REM (Rapid eye movement) sleep takes place every 90 minutes (or so), and this process is repeated throughout the night. It accounts for approximately 50% of an infant’s sleep cycle and 25% per cent of an adult’s cycle.

What is rapid eye movement sleep

REM sleep is thought to play an important role in memory, learning and mood. Most dreams occur during this period of sleep. Before moving into the REM sleep stage, the sleep cycle begins with non-REM sleep. The initial phase of REM lasts for usually 10 minutes, with each phase getting longer progressively. The last stage of REM sleep lasts for up to an hour.

During REM sleep, the brain and body go through several changes, including:

  • Irregular and fast breathing with rapid eye movements
  • Increased heart rate (near waking levels)
  • Changes in basal body temperature.
  • Raised blood pressure.
  • Active brain (as seen when a person is awake)
  • Increased consumption of oxygen by the brain
  • Twitching of limbs and face

REM sleep is also associated with maintaining important neural pathways and learning new information. Aside from brain activity and eye movements, in several cases, REM also incites the muscles to be temporarily paralyzed (except heart muscles and diaphragm). People experience “temporary paralysis”. It happens when the brain signals the spinal cord to block the movement of muscles. This lack of muscle activity is termed atonia. Researchers theorize it as a protective mechanism by design for preventing injury caused by acting out of our vivid dreams while sleeping.

REM sleep is associated with vivid dreams due to increased brain activity. As the muscles are immobilized, the brain remains active, and this state of sleep is known as “paradoxical sleep”.

What happens during REM?

This phenomenon/mechanism have puzzled researchers for decades. Recent researches have suggested that the brain switches to different types of mental imagery during this stage, which could account for the rapid movements of eyes, each one associated with tracking a new mental image, i.e., each rapid eye movement reflect the instant of new image creation or encounter in the brain. Dreaming exists to help us process memory. Rapid eye movement is related to the window of visual experience in a dream; During these movements, the sleeping brain captures the screenshots from the dream world inside our heads.

What happens during REM

REM exists to encode “procedural memory”, a type of memory that helps us sort out how to do things, i.e., creative problem solving and motor skills.

Non-REM sleep :

Before entering into the REM phase, the body goes through a non-REM phase of sleep, which comprises four stages, lasting for 5-10 minutes.

Stage 1: In this stage, you are in a very light sleep ( you are between being awake and asleep)

Stage 2: In this stage, you are in a slightly deeper sleep. Your heart rate slows down, and body temperature drops.

Stage 3 and 4: This stage comprises a restorative deep sleep phase, known as “delta sleep” or “slow-wave sleep”. In this stage, the supply of blood to muscles is increased. Meanwhile, the body grows and repairs the tissue. The release of hormones replenishes the energy stores of the body.

As people age, they tend to have less non-REM sleep. People under 30 experience at least 2 hours of restorative sleep per night, and older adults above 40 get just 30 minutes of this phase.

Why REM sleep is needed:  

Brain activity is hugely critical to a healthy mind, and REM sleep contributes much in this. REM is exactly the phase associated with the feeling of refreshment when you wake up ( after a good sleep). When sleep stages are interrupted, REM sleep is often sacrificed, as it is the last step in the sleep cycle (before it repeats itself.

During a night of uninterrupted sleep, our brain gets the opportunity to remove neurotoxins (for example, in the case of  Alzheimer’s disease, the body cleans up the waste products of related compound beta-amyloid).On the other hand, interrupted sleep results in less REM sleep, resulting in suppression of information processing in the brain, and hence a lazy mode of cleaning toxic compounds.

Why REM sleep is needed

People who do not take adequate sleep experience, daytime sleepiness and feeling of unfreshness are more likely to have diseases like Parkinson’s disease and Alzheimer’s disease.

REM sleep behaviour disorder (RBD) :

It is a neurological sleeping disorder in which the person enters the REM phase, but the gateway responsible for muscular paralysis is blocked abnormally, resulting in physical actions in resonance with the dream during sleep. It is somewhat a dangerous form of sleep disorder if something goes wrong while the person is acting out of his dream.

Sleepwalking is different from RBD, as sleepwalking is just a transition between stages in non REM cycles

REM sleep behaviour disorder (RBD)

Functions of REM sleep:

REM sleep is believed to benefit memory and learning. It also contributes to brain tissue development. A lack of REM sleep has bad implications for emotional and physical health.

Learning and memory:

When you cannot enter REM sleep, you feel difficulty remembering what you were taught before falling asleep. A study on rats has proved that just three days of REM sleep deprivation affects the rate of cell proliferation (cell number growth) in the part of the brain responsible for long term memory storage.

Central nervous system development:

Some researches have proved that REM sleep contributes in neural stimulation necessary for developing mature neural connections. These findings are proof of why infants need more REM sleep than adults.

Consequences of lack of REM sleep:

Lack of REM sleep is linked with:

  • Reduced coping skills: 

Some research indicated that the animals subjected to deprivation of REM sleep showed abnormalities in defensive responses and coping mechanisms in threatening situations.

  • Migraines: 

 Lack of REM sleep is linked to migraines.

  • Overweight:

A study has proved that reduced REM sleep is associated with weight gain

Central nervous system development