In which stage of sleep do we dream

Brain Basics: Understanding Sleep | National Institute of Neurological Disorders and Stroke


Sleep is an important part of your daily routine—you spend about one-third of your time doing it. Quality sleep – and getting enough of it at the right times -- is as essential to survival as food and water. Without sleep you can’t form or maintain the pathways in your brain that let you learn and create new memories, and it’s harder to concentrate and respond quickly.

Sleep is important to a number of brain functions, including how nerve cells (neurons) communicate with each other. In fact, your brain and body stay remarkably active while you sleep. Recent findings suggest that sleep plays a housekeeping role that removes toxins in your brain that build up while you are awake.

Everyone needs sleep, but its biological purpose remains a mystery. Sleep affects almost every type of tissue and system in the body – from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of disorders including high blood pressure, cardiovascular disease, diabetes, depression, and obesity.

Sleep is a complex and dynamic process that affects how you function in ways scientists are now beginning to understand. This booklet describes how your need for sleep is regulated and what happens in the brain during sleep.

Anatomy of Sleep

Several structures within the brain are involved with sleep.


The hypothalamus, a peanut-sized structure deep inside the brain, contains groups of nerve cells that act as control centers affecting sleep and arousal.  Within the hypothalamus is the suprachiasmatic nucleus (SCN) – clusters of thousands of cells that receive information about light exposure directly from the eyes and control your behavioral rhythm.  Some people with damage to the SCN sleep erratically throughout the day because they are not able to match their circadian rhythms with the light-dark cycle.  Most blind people maintain some ability to sense light and are able to modify their sleep/wake cycle.

The brain stem, at the base of the brain, communicates with the hypothalamus to control the transitions between wake and sleep.  (The brain stem includes structures called the pons, medulla, and midbrain.)  Sleep-promoting cells within the hypothalamus and the brain stem produce a brain chemical called GABA, which acts to reduce the activity of arousal centers in the hypothalamus and the brain stem.  The brain stem (especially the pons and medulla) also plays a special role in REM sleep; it sends signals to relax muscles essential for body posture and limb movements, so that we don’t act out our dreams.

The thalamus acts as a relay for information from the senses to the cerebral cortex (the covering of the brain that interprets and processes information from short- to long-term memory).  During most stages of sleep, the thalamus becomes quiet, letting you tune out the external world.   But during REM sleep, the thalamus is active, sending the cortex images, sounds, and other sensations that fill our dreams. 

The pineal gland, located within the brain’s two hemispheres, receives signals from the SCN and increases production of the hormone melatonin, which helps put you to sleep once the lights go down.  People who have lost their sight and cannot coordinate their natural wake-sleep cycle using natural light can stabilize their sleep patterns by taking small amounts of melatonin at the same time each day.  Scientists believe that peaks and valleys of melatonin over time are important for matching the body’s circadian rhythm to the external cycle of light and darkness.

The basal forebrain, near the front and bottom of the brain, also promotes sleep and wakefulness, while part of the midbrain acts as an arousal system.  Release of adenosine (a chemical by-product of cellular energy consumption) from cells in the basal forebrain and probably other regions supports your sleep drive.   Caffeine counteracts sleepiness by blocking the actions of adenosine.

The amygdala, an almond-shaped structure involved in processing emotions, becomes increasingly active during REM sleep. 

Sleep Stages and Mechanisms

Sleep Stages

There are two basic types of sleep:  rapid eye movement (REM) sleep and non-REM sleep (which has three different stages).  Each is linked to specific brain waves and neuronal activity.  You cycle through all stages of non-REM and REM sleep several times during a typical night, with increasingly longer, deeper REM periods occurring toward morning. 


Stage 1 non-REM sleep is the changeover from wakefulness to sleep.  During this short period (lasting several minutes) of relatively light sleep, your heartbeat, breathing, and eye movements slow, and your muscles relax with occasional twitches.  Your brain waves begin to slow from their daytime wakefulness patterns.


Stage 2 non-REM sleep is a period of light sleep before you enter deeper sleep.   Your heartbeat and breathing slow, and muscles relax even further.  Your body temperature drops and eye movements stop.  Brain wave activity slows but is marked by brief bursts of electrical activity.  You spend more of your repeated sleep cycles in stage 2 sleep than in other sleep stages.


Stage 3 non-REM sleep is the period of deep sleep that you need to feel refreshed in the morning.  It occurs in longer periods during the first half of the night.  Your heartbeat and breathing slow to their lowest levels during sleep.  Your muscles are relaxed and it may be difficult to awaken you.  Brain waves become even slower.


REM sleep first occurs about 90 minutes after falling asleep.  Your eyes move rapidly from side to side behind closed eyelids.  Mixed frequency brain wave activity becomes closer to that seen in wakefulness.  Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels.   Most of your dreaming occurs during REM sleep, although some can also occur in non-REM sleep.  Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams.  As you age, you sleep less of your time in REM sleep.  Memory consolidation most likely requires both non-REM and REM sleep.

Sleep Mechanisms

Two internal biological mechanisms–circadian rhythm and homeostasis–work together to regulate when you are awake and sleep.  

Circadian rhythms direct a wide variety of functions from daily fluctuations in wakefulness to body temperature, metabolism, and the release of hormones.  They control your timing of sleep and cause you to be sleepy at night and your tendency to wake in the morning without an alarm.  Your body’s biological clock, which is based on a roughly 24-hour day, controls most circadian rhythms.  Circadian rhythms synchronize with environmental cues (light, temperature) about the actual time of day, but they continue even in the absence of cues.  


Your body's biological clock is based on a 24-hour day and controls most circadian rhythms. These rhythms affect a variety of functions including body temperature (represented as the white line on the chart above). Melatonin - a hormone released by the pineal gland - helps you feel sleepy once the lights go down. The peaks and valleys of melatonin (represented as the gold line above) are important for matching the body's circadian rhythm to the external cycle of light and darkness.

Sleep-wake homeostasis keeps track of your need for sleep.  The homeostatic sleep drive reminds the body to sleep after a certain time and regulates sleep intensity.  This sleep drive gets stronger every hour you are awake and causes you to sleep longer and more deeply after a period of sleep deprivation.

Factors that influence your sleep-wake needs include medical conditions, medications, stress, sleep environment, and what you eat and drink.  Perhaps the greatest influence is the exposure to light.   Specialized cells in the retinas of your eyes process light and tell the brain whether it is day or night and can advance or delay our sleep-wake cycle.  Exposure to light can make it difficult to fall asleep and return to sleep when awakened.

Night shift workers often have trouble falling asleep when they go to bed, and also have trouble staying awake at work because their natural circadian rhythm and sleep-wake cycle is disrupted.  In the case of jet lag, circadian rhythms become out of sync with the time of day when people fly to a different time zone, creating a mismatch between their internal clock and the actual clock. 

How Much Sleep Do You Need?


Sleep needs change with age as shown on the chart above. Initially, babies sleep 16-18 hours a day. School-age children and teens need about 9.5 hours of sleep each night. Most adults require 7-9 hours of sleep at night. However, older adults (age 60 and above) tend to sleep for shorter periods at night.

Your need for sleep and your sleep patterns change as you age, but this varies significantly across individuals of the same age.   There is no magic “number of sleep hours” that works for everybody of the same age.  Babies initially sleep as much as 16 to 18 hours per day, which may boost growth and development (especially of the brain).  School-age children and teens on average need about 9.5 hours of sleep per night.  Most adults need 7-9 hours of sleep a night, but after age 60, nighttime sleep tends to be shorter, lighter, and interrupted by multiple awakenings.  Older people are also more likely to take medications that interfere with sleep. 

In general, people are getting less sleep than they need due to longer work hours and the availability of round-the-clock entertainment and other activities. 

Many people feel they can "catch up" on missed sleep during the weekend but, depending on how sleep-deprived they are, sleeping longer on the weekends may not be adequate.

Dreaming and Sleep Tracking


Everyone dreams.  You spend about 2 hours each night dreaming but may not remember most of your dreams.   Its exact purpose isn’t known, but dreaming may help you process your emotions.  Events from the day often invade your thoughts during sleep, and people suffering from stress or anxiety are more likely to have frightening dreams.  Dreams can be experienced in all stages of sleep but usually are most vivid in REM sleep.  Some people dream in color, while others only recall dreams in black and white.


Tracking Sleep Through Smart Technology

Millions of people are using smartphone apps, bedside monitors, and wearable items (including bracelets, smart watches, and headbands) to informally collect and analyze data about their sleep.  Smart technology can record sounds and movement during sleep, journal hours slept, and monitor heart beat and respiration.  Using a companion app, data from some devices can be synced to a smartphone or tablet, or uploaded to a PC.  Other apps and devices make white noise, produce light that stimulates melatonin production, and use gentle vibrations to help us sleep and wake.

The Role of Genes and Neurotransmitters

Chemical signals to sleep     

Clusters of sleep-promoting neurons in many parts of the brain become more active as we get ready for bed.  Nerve-signaling chemicals called neurotransmitters can “switch off” or dampen the activity of cells that signal arousal or relaxation.  GABA is associated with sleep, muscle relaxation, and sedation.  Norepinephrine and orexin (also called hypocretin) keep some parts of the brain active while we are awake.  Other neurotransmitters that shape sleep and wakefulness include acetylcholine, histamine, adrenaline, cortisol, and serotonin.

Genes and sleep

Genes may play a significant role in how much sleep we need.  Scientists have identified several genes involved with sleep and sleep disorders, including genes that control the excitability of neurons, and "clock" genes such as Per, tim, and Cry that influence our circadian rhythms and the timing of sleep.   Genome-wide association studies have identified sites on various chromosomes that increase our susceptibility to sleep disorders.  Also, different genes have been identified with such sleep disorders as familial advanced sleep-phase disorder, narcolepsy, and restless legs syndrome.  Some of the genes expressed in the cerebral cortex and other brain areas change their level of expression between sleep and wake.  Several genetic models–including the worm, fruit fly, and zebrafish–are helping scientists to identify molecular mechanisms and genetic variants involved in normal sleep and sleep disorders.  Additional research will provide better understand of inherited sleep patterns and risks of circadian and sleep disorders. 


Sleep studies

Your health care provider may recommend a polysomnogram or other test to diagnose a sleep disorder.  A polysomnogram typically involves spending the night at a sleep lab or sleep center.  It records your breathing, oxygen levels, eye and limb movements, heart rate, and brain waves throughout the night.   Your sleep is also video and audio recorded.  The data can help a sleep specialist determine if you are reaching and proceeding properly through the various sleep stages.  Results may be used to develop a treatment plan or determine if further tests are needed.

Tips for Getting a Good Night's Sleep


Getting enough sleep is good for your health.  Here are a few tips to improve your sleep:

  • Set a schedule – go to bed and wake up at the same time each day.
  • Exercise 20 to 30 minutes a day but no later than a few hours before going to bed.
  • Avoid caffeine and nicotine late in the day and alcoholic drinks before bed.
  • Relax before bed – try a warm bath, reading, or another relaxing routine.
  • Create a room for sleep – avoid bright lights and loud sounds, keep the room at a comfortable temperature, and don’t watch TV or have a computer in your bedroom.
  • Don’t lie in bed awake.  If you can’t get to sleep, do something else, like reading or listening to music, until you feel tired.  
  • See a doctor if you have a problem sleeping or if you feel unusually tired during the day.  Most sleep disorders can be treated effectively.

Hope Through Research

Scientists continue to learn about the function and regulation of sleep.  A key focus of research is to understand the risks involved with being chronically sleep deprived and the relationship between sleep and disease.  People who are chronically sleep deprived are more likely to be overweight, have strokes and cardiovascular disease, infections, and certain types of cancer than those who get enough sleep.  Sleep disturbances are common among people with age-related neurological disorders such as Alzheimer’s disease and Parkinson’s disease.  Many mysteries remain about the association between sleep and these health problems.  Does the lack of sleep lead to certain disorders, or do certain diseases cause a lack of sleep?  These, and many other questions about sleep, represent the frontier of sleep research.

REM & NREM, Sleep Stages, Good Sleep Habits & More

What is sleep?

You may think nothing is happening when you sleep. But parts of your brain are quite active during sleep. And enough sleep (or lack of it) affects your physical and mental health. When you sleep, your body has a chance to rest and restore energy. A good night’s sleep can help you cope with stress, solve problems or recover from illness. Not getting enough sleep can lead to many health concerns, affecting how you think and feel.

During the night, you cycle through two types of sleep: non-rapid eye movement (non-REM) sleep and rapid eye movement (REM) sleep. Your brain and body act differently during these different phases.

What happens in the brain during sleep?

Researchers continue to study sleep and its effect on us. While we’ve learned a lot about sleep, there’s still much that’s unknown.

We know that brain chemicals are very involved in our sleep cycle. Neurotransmitters are chemicals that help the nerves communicate. They control whether we’re awake or asleep, depending on which neurons (nerve cells) they’re acting on:

  • Neurons in the brainstem (where the brain and spinal cord meet) produce neurotransmitters called serotonin and norepinephrine. These chemicals keep our brain active when we’re awake.
  • Neurons located at the base of the brain are responsible for us falling asleep. It seems these neurons turn off the signals that keep us awake.

Why do we need sleep?

Sleep helps us in many ways. We need it for:

  • Growth: In children and young adults, deep sleep (sleep that’s harder to wake from) supports growth. The body releases growth hormone during this type of sleep. The body also increases production of proteins, which we need for cell growth and to repair damage.
  • Nervous system function: A lack of sleep affects our memory, performance and ability to think clearly. If a person is severely sleep deprived, they may even experience neurological problems such as mood swings and hallucinations. Sleep also helps our nerve cells. They can repair themselves, so they function at their best. And certain nerve connections get a chance to turn on, strengthening our brain and thinking ability.
  • Survival: Researchers don’t fully understand why sleep is so essential. But studies in animals have shown that getting deprived of REM sleep can shorten lifespans. Lack of sleep may harm the immune system, which protects us from infections.
  • Well-being: People who don’t get enough sleep are at higher risk for developing various health conditions including obesity, diabetes and heart problems.

What are the stages of sleep?

When you sleep, your brain goes through natural cycles of activity. There are four total stages of sleep, divided into two phases:

  • Non-REM sleep happens first and includes three stages. The last two stage of non-REM sleep is when you sleep deeply. It’s hard to wake up from this stage of sleep.
  • REM sleep happens about an hour to an hour and a half after falling asleep. REM sleep is when you tend to have vivid dreams.

As you sleep, your body cycles through non-REM and REM sleep. You usually start the sleep cycle with stage 1 of non-REM sleep. You pass through the other stages of non-REM sleep, followed by a short period of REM sleep. Then the cycle begins again at stage 1.

A full sleep cycle takes about 90 to 110 minutes. Your first REM period is short. As the night goes on, you’ll have longer REM sleep and less deep sleep.

What is non-REM sleep?

Three stages make up non-REM sleep.

Stage 1:

This stage of light sleeping lasts for five to 10 minutes.

  • Everything starts to slow down, including your eye movement and muscle activity.
  • Your eyes stay closed. If you get woken from stage 1 sleep, you may feel as if you haven’t slept at all. You may remember pieces of images.
  • Sometimes, you may feel like you’re starting to fall and then experience a sudden muscle contraction. Healthcare providers call this motion hypnic myoclonic or hypnic jerk. Hypnic jerks are common and not anything to be concerned about as this occurrence is unlikely to cause any complications or side effects.

Stage 2:

  • This period of light sleep features periods of muscle tone (muscles partially contracting) mixed with periods of muscle relaxation.
  • Your eye movement stops, heart rate slows and body temperature decreases.
  • Brain waves become slower. Occasionally, you’ll have a burst of rapid waves called sleep spindles.
  • Your body prepares to enter deep sleep.

Stages 3

  • This stage is deep sleep.
  • During this stage, your brain produces delta waves, very slow brain waves.
  • It’s hard for someone to wake you up during this stage.
  • You have no eye movement or muscle activity.
  • If you’re woken up, you may feel groggy and disoriented for a few minutes.

What happens during non-REM sleep?

During non-REM stages, your body:

  • Builds bone and muscle.
  • Repairs and regenerates tissues.
  • Strengthens the immune system.

As you age, you get less non-REM sleep. Older adults get less deep sleep than younger people.

What is REM sleep?

When you enter REM sleep, brain activity increases again, meaning sleep is not as deep. The activity levels are like when you’re awake. That’s why REM sleep is the stage where you’ll have intense dreams.

At the same time, major muscles that you normally control (such as arms and legs) can’t move. In effect, they become temporarily paralyzed.

Usually, REM sleep arrives about an hour and a half after you go to sleep. The first REM period lasts about 10 minutes. Each REM stage that follows gets longer and longer.

The amount of REM sleep you experience changes as you age. The percentage of REM sleep:

  • Is highest during infancy and early childhood.
  • Declines during adolescence and young adulthood.
  • Declines even more as you get older.

What else happens to the body in REM sleep?

Besides increased brain activity and muscle relaxation, your body goes through a series of changes during REM sleep. These changes include:

  • Faster breathing.
  • Increased heart rate and blood pressure.
  • Penile erections.
  • Rapid eye movement.

What affects sleep quality?

Chemical signals in the brain influence our sleep and wake cycles. Anything that shifts the balance of these neurotransmitters can make us feel drowsier or more awake. For example:

  • Alcohol may help people fall into a light sleep. But it reduces the deeper stages of sleep and REM sleep and leads to more disrupted sleep.
  • Caffeine and pseudoephedrine (drug ingredient) can stimulate the brain. They may cause insomnia, an inability to sleep. Watch out for caffeinated drinks such as coffee and drugs such as diet pills and decongestants.
  • Medications such as antidepressants can cause less REM sleep.
  • People who smoke heavily often sleep lightly and have less REM sleep. They may wake up after a few hours because they experience nicotine withdrawal.
  • Very hot or cold temperatures can disrupt REM sleep. We’re less able to regulate body temperature during REM sleep.

How much sleep do I need?

Many factors affect how much sleep you need. Age is a big factor:

  • Infants need about 16 hours a day.
  • Toddlers and preschoolers need about 12 hours.
  • Teenagers need about nine hours.
  • Adults need seven to eight (though some are fine with five and others need closer to 10).
  • Pregnant people often need more sleep during the first trimester.

What is a sleep debt?

If you haven’t slept well or long enough for a few days, you might create a sleep debt. Once your debt builds up, you may feel physically and mentally exhausted. Try to make sure you get enough sleep every night to avoid creating this debt. You can’t necessarily make up your debt by sleeping a lot on the weekends. It’s best to get enough sleep all week long.

Can we adapt to needing less sleep?

Generally, people don’t adapt to getting less sleep than they need. You may feel like you’re used to reduced sleep, but it still affects your function. For example, it can harm your judgment and reaction time.

What is sleep deprivation?

When you’re sleep deprived, you’re not getting the total amount of sleep you need. Signs of sleep deprivation include:

  • Falling asleep within a few minutes of lying down.
  • Feeling drowsy during the day.
  • Nodding off for microsleeps — short periods of sleep during the day when you’re otherwise awake.
  • Sleep deprivation can be dangerous. Driving while tired causes about 100,000 car accidents each year, according to the National Highway Traffic Safety Administration. It also causes 1,500 deaths. If you feel tired on the road, pull over. It’s not safe to drive if you’re drowsy.

What are sleep disorders?

According to the American Sleep Association, at least 40 million Americans experience sleep disorders each year. Another 20 million have occasional sleep issues. These disorders cause sleep deprivation, leading to problems with work, school, driving and social activities.

There are more than 70 sleep disorders. A few, known as disruptive sleep disorders, lead to moving around or making sounds. Other sleep disorders involve food. And some sleep disorders overlap with psychiatric conditions. If you have problems with sleep or feel very tired, talk to your healthcare provider about a possible sleep disorder.

Some of the most common sleep disorders include:

  • Insomnia disorder: Many people experience insomnia at some point in their lives, with trouble falling or staying asleep. Sleeping pills can help in the short-term but behavioral strategies to improve sleep including cognitive behavioral therapy for Insomnia (CBT-i) is a much better long term solution.
  • Narcolepsy: You may suddenly fall asleep during the day, even if you had a good sleep the night before. These “sleep attacks” can last a few seconds or up to 30 minutes. Talk to your provider about your symptoms and additional testing will need to be completed to diagnosis this sleep disorder.
  • Restless legs syndrome (RLS): You may feel unpleasant sensations in your legs (such as prickling or tingling). You may also have an urge to move your legs to get relief. If you have RLS, talk to your healthcare provider about medication to help improve symptoms.
  • Sleep apnea: You may experience periods of interrupted breathing while you sleep, a condition called sleep apnea. Often, getting polysomnography (sleep study) in a sleep center is the best way to get properly diagnosed and treated. Sometimes, weight loss or not sleeping on your back can help. But you may need a special device to help you breathe while you sleep.
  • Snoring: People who regularly snore can have disturbed sleep. They can also disturb the sleep of their bed partner. Snoring often leads to feeling tired during the day. Several treatment options are available for snoring.

What are good sleep habits?

Good sleep habits, also called good sleep hygiene, are practices to help you get enough quality sleep.


  • Have a sleep schedule: Go to sleep and wake up around the same time every day, even on weekends and vacations.
  • Clear your mind before bed: Make a to-do list early in the evening, so you won’t stay awake in bed and worry about the next day.
  • Create a good sleep environment: Make sure your bed and pillows are comfortable. Turn down the lights and avoid loud sounds. Keep the room at a comfortable temperature.
  • Exercise every day: Stay active but try to avoid exercising during the few hours right before bed.
  • Relax: Before bed, take a warm bath, read or do another relaxing activity.
  • See your healthcare provider: If you’ve been having trouble sleeping or feel extra drowsy during the day, talk to your provider. There are many treatments available for sleep disorders.


  • Consume caffeine, nicotine and alcohol late in the day: These substances can interfere with your ability to fall and stay asleep.
  • Lie in bed awake: It’s better to do a soothing activity, like reading, until you feel tired.
  • Nap during the day: A short nap (less than 30 minutes) is OK if you’re very sleepy. But try to avoid naps after 3 p.m.
  • Think negative thoughts: Try to avoid a negative mindset when going to bed, such as, “If I don’t get enough sleep now, I won’t get through my day tomorrow!”
  • Use electronics right before bed: Electronics, such as your phone or tablet, can interfere with your body’s production of melatonin. This hormone gets released before bed to help you feel tired.

A note from Cleveland Clinic

Far from being a state of doing nothing, sleep is an essential part of our lives. It helps our body rest, recharge and repair. There are four sleep stages — three in the non-REM phase plus REM sleep. Many factors can affect sleep quality, including the food and drink you consume before bed and room temperature. Many people experience trouble sleeping now and then. But if you think you may have a sleep disorder, talk to your healthcare provider. Common sleep disorders include insomnia (trouble falling asleep) and sleep apnea (breathing trouble during sleep). Your provider can help you get the diagnosis and treatment you need.

Sleep Optimization: How to sleep less but better

  • David Robson
  • BBC Worklife

Image copyright Getty Images

Scientists have already learned how to deepen and speed up the recovery processes that occur in our brain during sleep. Will it make us feel better even when we go to bed too late and wake up too early?

We often talk about our sleep difficulties with some pride. After all, they testify that we lead an extremely busy life.

Let's remember Thomas Edison, Margaret Thatcher - yes, the same Donald Trump. All of them are famous for their short night rest - 4-5 hours of sleep, much less than the 7-9 hours recommended by doctors for adults.

  • We cut our own sleep, and the consequences are very disturbing
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Many of us seem to follow suit: according to the US Centers for Disease Prevention and Control, more than a third of US adults regularly lack sleep.

The consequences are known - from memory impairment to increased risk of infectious diseases, from difficulty making decisions to obesity. But they are often ignored.

Alas, when our work needs exceed our normal daily schedule, the first thing we sacrifice is hours of sleep.

But if we could optimize the hours we spend sleeping, make them more efficient? Would we then need less time to sleep, and would it be deeper?

This possibility is closer than we think. Techniques for optimizing sleep already exist, and experiments around the world are proving that we can improve the efficiency of our brains at night.

First we speed up our deep sleep, and then we increase the quality of our rest.

Do you think it sounds too nice to be true? Let's figure it out.

Slowing down the rhythm

During a typical night, the brain goes through different stages of sleep, each with its own characteristic "brain wave" pattern. At the same time, neurons in different areas of the brain work synchronously, in a certain rhythm (like a large crowd chanting something in unison).

During REM sleep, also known as rapid eye movement (REM) sleep, the rhythm of neurons is relatively fast - that's when we usually dream.

But at certain moments our eyes stop moving, dreams stop dreaming and the rhythm of brain activity drops to one "beat" per second.

And here we plunge into that very deep unconscious state, which is called the phase of slow sleep.

It is this stage that is of most interest to scientists studying the possibilities of optimizing sleep.

Image copyright, Getty Images

Image caption,

Margaret Thatcher, among other things, was known for sleeping four to five hours a night, at least during her years as British Prime Minister

Research since the 1980s has shown that non-REM sleep is critical to maintaining normal brain function. During it, the corresponding areas of the brain transfer memories of what happened during the day from the category of short-term memory to long-term - so that we do not forget what we have learned and learned.

"Slow-wave sleep facilitates this transfer of information," says Jan Born, Head of the Department of Medical Psychology and Behavioral Neuroscience at the University of Tübingen (Germany).

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Slow-wave sleep also triggers blood and spinal fluid flow to the brain, thus "flushing out" potentially damaging neurons " blockages".

At the same time, levels of cortisol (hydrocortisone, the “stress hormone”) are lowered, which helps to restore the immune system, preparing it for future attacks of infections.

Image copyright, Getty Images

Image caption,

Many companies are now working to develop methods to help their customers achieve deeper, more NREM sleep, much like children do.

Born and other scientists wondered if we could to improve the quality of sleep and, in particular, the phases of non-REM sleep so much that it will improve our daytime functioning?

One of the most promising techniques is to use a sort of metronome for the sleeping brain. Participants in the experiments put on a kind of helmet on their heads, which captures the phases of their brain activity during sleep - including when they are immersed in the slow phase.

And then the device begins to reproduce short impulses, barely audible sounds with a frequency that matches the brain impulses of the non-REM sleep phase.

These sounds are not loud enough to wake a sleeping person, but a person subconsciously perceives them.

Bourne came to the conclusion that such gentle sound stimulation is quite sufficient to ensure that the correct brain rhythms enhance the state of deep sleep.

  • Circadian rhythms: why is daylight so important for good sleep?
  • Scientists have found how sound sleep can prevent the onset of Alzheimer's disease slept with a device that produced no stimulation.

    The signals sent by the device changed the hormonal balance, helped to reduce the level of cortisol in the body.

    To date, none of the participants in the experiments have reported adverse effects or side effects of such brain stimulation, Born says.

    For sound sleep - to the store

    Most of the experiments to deepen the phase of non-REM sleep involved small groups of young and healthy volunteers. So, in order to be fully convinced of the benefits of such techniques, research should be wider and in groups with more diverse composition.

    But the technology has already made its way into some household devices - mainly in the form of headbands worn at night on the head.

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    The French start-up Dreem, for example, produces such a headband (costs about 400 euros), as in the experiments described above, stimulating the brain with sound impulses that immerse a person in a phase of slow sleep. The effectiveness of this device is confirmed by a peer-reviewed scientific study.

    The French gadget comes with a mobile application that analyzes your sleep and offers practical advice and exercises to improve it - including meditation and breathing exercises.

    Philips, the manufacturer of the SmartSleep device, makes it clear that it wants to help alleviate the negative effects of sleep deprivation.

    The device is for those people "who, for whatever reason, simply can't afford to get as much sleep as their body needs," says David White, Chief Scientist at Philips.

    Image copyright, Getty Images

    Image caption,

    Philips joined the research to improve sleep efficiency with its own device for sleep-deprived people

    Launched in 2018. Like the Dreem, it's a headband that detects electrical brain activity and periodically sends out short beeps to stimulate the vibrations that are characteristic of non-REM sleep.

    The gadget relies on software that offers the optimal level of stimulation for a particular person (SmartSleep is currently only available in the US, its price is 39$9).

    David White agrees that such devices are not a complete substitute for a good night's sleep. But, he says, those who suffer from sleep deprivation are extremely difficult to convince of the need to change their lifestyle. And the device should at least help them feel better during the day.

    Philips' own research has reportedly confirmed that SmartSleep stimulates slow-wave sleep in those who are regularly sleep deprived and mitigates the impact of this sleep loss on the effectiveness of nighttime memory consolidation.

    No doubt, in the future, new experiments will lead to new devices and innovative ways to optimize sleep.

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    Auror Perrault of Concordia University (Montreal) recently tested a bed that gently rocked back and forth every four seconds, much like a cradle with a baby.

    According to her, her colleague suggested this after she had a baby and had to rock him to sleep. Scientists have a question: but will it work with adults too?

    Image copyright Dreem

    Image caption

    French startup Dreem's device uses sound brain stimulation to improve sleep quality. Similar products are starting to appear on the market

    Indeed, it turned out that the participants in the experiment fell into slow sleep faster and spent more time in it. Their brains synchronized with external movement.

    As expected, they reported feeling more rested afterwards. In addition, this was accompanied by positive effects on their memory.

    If such a bed is available for sale, it will perform the same function as head-mounted devices.

    Perro is particularly interested in whether she will help the elderly. As we age, the amount of time we spend in non-REM sleep decreases, and memory problems may be associated with this.

    Perrault hopes that the gently rocking bed will help counter this.

    Sleep anyway

    While such studies are at the very beginning of their journey, they are nevertheless promising. Perrault and Bourne are optimistic about the potential of commercial products that use sound pulses for health purposes.

    Perrault stresses that more research is needed on the effectiveness of such methods - and no longer in the laboratory. "It's great that they keep trying to use external stimulation - we know it works," says Perrault.

    Image copyright, Getty Images

    Image caption,

    Some research has found that long-known environmental stimuli, like bed rocking, can help adults sleep better too

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    Will these techniques have long-term effects? We know that chronic sleep deprivation increases the risk of developing diabetes and even Alzheimer's syndrome. Can artificially optimized sleep reduce these risks?

    For now, the only way to ensure you get all the benefits of healthy sleep (both in the short and long term) is to make sure you get enough sleep each night.

    Whether or not to test the devices described here is up to you. But you should definitely try going to bed early more often, not drinking alcohol and caffeine before bed, and not browsing social media and your favorite Internet sites for too long while lying in bed. All this harms the quality of sleep.

    Our brain cannot function properly without the recharge that sleep provides. And it would be better for us not to oversleep the moment when it will be too late to fix something.


    Read the original English version of this article at BBC Worklife .

    Sleep phases: non-REM and REM sleep

    We sleep for a third of our lives. If its duration is 90 years, sleep takes 30 years. A lot, isn't it?

    It is important for us to rest every day. Our body goes into a special mode - the organs work more calmly, the nervous system is disconnected from the outside world.

    Good sleep fills us with resources, strengthens memory, unloads the psyche, reduces stress, helps eliminate toxins and melanin production. To replenish health, we need an eight-hour sleep cycle. It consists of five phases, which last 15-20 minutes and one and a half to two hours. Slow and REM sleep is in every cycle. To make it easier to study your sleep, you can use fitness bracelets.

    Slow-wave sleep - stage 1 (falling asleep)

    Slow-wave sleep is the stage of sleep in which we move from activity to sleep. It is often referred to as dormancy. It lasts about 10-15 minutes if you follow the regimen and are healthy. If you fall asleep without having time to lie down on the pillow, then you are too tired, you need to go to bed earlier.

    Slow-wave sleep - stage 2 (light sleep)

    Light sleep is also called immersion. Lasts about 20 minutes. At this time, the body temperature decreases, the heartbeat slows down, consciousness turns off. Physical strength is also restored. But, for example, the hearing becomes aggravated. You can wake up from a slight noise. If you wake up at this stage, you can feel rested. Especially if you fell asleep during the day. But it will not be difficult to continue the dream, it will be easy to fall asleep again.

    Slow-wave sleep - stage 3 (delta sleep)

    This phase of deep sleep lasts about 40 minutes. It is shorter in the morning than in the evening. In this phase, it is impossible to wake up on your own. If we are awakened, we will be confused: we will not immediately find out where we are and what is happening. At this stage of sleep, you may have a nightmare, talkativeness in a dream and sleepwalking.

    Slow-wave sleep - stage 4 (deep sleep)

    The slowest phase of sleep is deep sleep. Our body is fully restored, the psyche calms down. It is this dream that strengthens the immune system, allows us to look good, be calmer. Lasts about 40 minutes. If we are awakened, we will certainly want to sleep more. It is important to slowly get out of this phase of sleep, to let yourself wake up.

    REM sleep - stage 5

    The phase of REM sleep, in which the brain is actively working and we see dreams. Lasts about 10-20 minutes. The temperature rises, the heartbeat becomes faster. The subconscious works well. If we are awakened at this stage of sleep, we will be able to tell in detail what we dreamed about.

    REM sleep and deep sleep alternate during the night. Some phases we go through 2-3 times.

    Sleep deprivation has consequences. At us attention, memory worsen and thinking is slowed down. Immunity decreases, the likelihood of getting sick becomes higher.

    Learn more