Understanding Rem Sleep: The Nih Perspective

REM sleep is a fascinating phenomenon that has puzzled sleep researchers for decades. It is characterised by relaxed muscles, rapid eye movement, irregular breathing, an elevated heart rate, and increased brain activity. But what is it, and why do we need it?

What is REM Sleep?

REM (rapid eye movement) sleep is the fourth of four stages of sleep, first discovered in the 1950s when scientists noticed that sleeping infants' eyes moved rapidly from side to side. During REM sleep, your brain activity is similar to when you are awake, and your eyes move rapidly behind closed eyelids. Your breathing becomes irregular, and your heart rate rises. Your muscles also become temporarily paralysed, preventing you from acting out your dreams.

Why Do We Need REM Sleep?

REM sleep plays a crucial role in several important functions, including:

- Memory Consolidation: Your brain processes new information and commits it to memory during REM sleep.

- Emotional Processing: Your brain processes emotions during REM sleep, and the amygdala, which is involved in processing emotions, is more active during this stage.

- Brain Development: Newborns spend most of their sleep time in REM sleep, suggesting that it may promote brain development.

- Dreaming: While dreams can occur during non-REM sleep, they are usually more vivid during REM sleep.

- Wakefulness Preparation: The activation of the central nervous system during REM sleep may help prepare us to wake up.

How Much REM Sleep Do We Need?

The amount of REM sleep we need changes throughout our lives. Newborns spend up to eight hours in REM sleep per day, while adults only need around two hours per night. The proportion of REM sleep also varies among different species. Horses and elephants, for example, can get by with little to no REM sleep, while cats and ferrets may spend up to eight hours per day in this stage.

What Happens If We Don't Get Enough REM Sleep?

While the effects of REM sleep deprivation are not yet fully understood, multiple studies suggest that it interferes with memory formation. Chronic sleep deprivation has been linked to various health issues, including diabetes, depression, obesity, and cardiovascular disease.

What happens during REM sleep?

During REM sleep, your eyes move rapidly behind your closed eyes, your heart rate speeds up, and your breathing becomes irregular. Your brain is highly active during this stage, and your brain waves become more variable. Your body operates similarly to how it does when you're awake, except your eyes are closed and you experience a temporary loss of muscle tone. This is thought to be a protective measure to stop you from acting out your dreams and injuring yourself. However, this hypothesis is losing credibility now that scientists know we can experience dreams during non-REM sleep when our bodies are not paralysed.

REM sleep is the fourth of four stages of sleep. You experience your first cycle of REM sleep about 60 to 90 minutes after falling asleep. As part of a full night's sleep, you cycle through four stages of sleep multiple times: three stages of non-REM sleep, followed by one stage of REM sleep. Each cycle through all the sleep stages takes 90 to 120 minutes to complete. With each new cycle, you spend increasing amounts of time in REM sleep, with most of your REM sleep taking place in the second half of the night.

REM sleep is important for dreaming, memory, emotional processing, and healthy brain development. A majority of your dreams take place during REM sleep, but it is not the only stage in which dreams occur. The dreams you experience in REM sleep are usually more vivid than non-REM sleep dreams. Your brain processes emotions during REM sleep, and your amygdala, the part of your brain that processes emotions, activates during this stage. During REM sleep, your brain processes new learnings and motor skills from the day, committing some to memory, maintaining others, and deciding which ones to delete.

When does REM sleep occur?

REM sleep—which stands for rapid-eye movement sleep—occurs at intervals throughout the night. Sleep typically follows a pattern, beginning with non-REM sleep, followed by a transition to REM sleep.

During non-REM sleep, the body relaxes and the brain waves slow down, with the heart rate and breathing regulated and slowed. This is the period of sleep where the body repairs muscles and tissues, and the immune system is boosted. The transition to REM sleep occurs about 90 minutes after falling asleep. The first period of REM sleep is short, but as sleep progresses, the REM periods lengthen, and the non-REM periods shorten.

Typically, a person will experience this cycle four or five times during a typical night's sleep. The REM cycles tend to be longer in the second half of the night.

The REM phase of sleep is when the brain is most active and the eyes dart rapidly behind closed lids. Dreaming occurs during this stage, and the body is temporarily paralysed as the brain sends signals to the spinal cord and muscles. This is known as REM atonia and serves to protect sleepers from acting out their dreams.

Why is REM sleep important?

REM sleep is important for several reasons, including brain development, memory consolidation, emotional processing, and dreaming.

During REM sleep, the brain prunes its synapses, improving memory and problem-solving abilities. It also processes emotional memories, including those associated with fear, and is thought to aid in the development of the central nervous system.

REM sleep is also when most dreams occur. The brain is highly active during this stage, with brain waves similar to those when awake. The body, however, is temporarily paralysed, which prevents sleepers from acting out their dreams.

REM sleep is particularly important for infants and children, whose brains are still developing. Newborns spend eight hours in REM sleep each day, and this gradually decreases to around 20% of total sleep time by age 20.

A good night's sleep, therefore, is essential to ensure sufficient REM sleep, which plays a critical role in overall health and well-being.

How much REM sleep do you need?

REM sleep, or rapid eye movement sleep, is the fourth of four stages of sleep. It is characterised by relaxed muscles, quick eye movement, irregular breathing, elevated heart rate, and increased brain activity. It is also associated with dreaming and memory consolidation.

There is no official agreement on how much REM sleep is needed but it is believed to be important for dreaming, and experts think that dreaming helps process emotions. For most adults, REM sleep makes up about 25% of total sleep, which seems to be healthy. On average, adults need around two hours of REM sleep each night.

The amount of REM sleep needed changes throughout our lives. Newborn babies spend eight hours in REM sleep each day, while school-age children and teens need about 9.5 hours of sleep per night. As we get older, we need less REM sleep.

What happens if you don't get enough REM sleep?

REM sleep is the fourth of four total stages of sleep. It is characterised by relaxed muscles, quick eye movement, irregular breathing, elevated heart rate, and increased brain activity. During REM sleep, the brain is highly active, and the body operates similarly to how it does when awake, except the eyes are closed and there is a temporary loss of muscle tone.

Missing out on REM sleep is not recommended, as it can lead to sleep deprivation, which has various effects on health and well-being. Signs of sleep deprivation include:

• Difficulty concentrating during the day
• Excessive daytime sleepiness
• Forgetfulness or poor memory
• Fatigue
• Irritability
• Changes in mood and memory
• Issues with cognition and problem-solving

Over time, chronic sleep deprivation is linked to health conditions such as:

• Diabetes
• Depression
• Obesity
• Cardiovascular disease
• Cancer
• Stroke
• Neurodegenerative diseases (e.g. Alzheimer's)

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