Dreams and rem sleep
The Possible Functions of REM Sleep and Dreaming - Neuroscience
Despite this wealth of descriptive information about the stages of sleep, the functional purposes of the various sleep states are not known. Whereas most sleep researchers accept the idea that the purpose of non-REM sleep is at least in part restorative, the function of REM sleep remains a matter of considerable controversy.
A possible clue about the purposes of REM sleep is the prevalence of dreams during these epochs of the sleep cycle. The occurrence of dreams can be tested by waking volunteers during either non-REM or REM sleep and asking them if they were dreaming. Subjects awakened from REM sleep recall elaborate, vivid, hallucinogenic and emotional dreams, whereas subjects awakened during non-REM sleep report fewer dreams, which, when they occur, are more conceptual, less vivid and less emotion-laden.
Dreams have been studied in a variety of ways, perhaps most notably within the psychoanalytic framework of revealing unconscious thought processes considered to be at the root of neuroses. Sigmund Freud's The Interpretation of Dreams, published in 1900, speaks eloquently to the complex relationship between conscious and unconscious mentation. It is by no means agreed upon, however, that dreams have the deep significance that Freud and others have given them, and the psychoanalytic interpretation of dreams has recently fallen into disfavor. Nevertheless, most people probably give some credence to the significance of dream content, at least privately. In more recent studies of dreams, about 65% are associated with sadness, apprehension, or anger; 20% with happiness or excitement; and, somewhat surprisingly, only 1% with sexual feelings or acts.
Adding to the uncertainty about the purposes of REM sleep and dreaming is the fact that deprivation of REM sleep in humans for as much as two weeks has little or no obvious effect on behavior. Such studies have been done by waking volunteers whenever their EEG recordings showed the characteristic signs of REM sleep. Although the subjects in these experiments compensate for the lack of REM sleep by having more of it after the period of deprivation has ended, they suffer no obvious adverse effects.
Similarly, patients taking certain antidepressants (MAO inhibitors) have little or no REM sleep, yet show no obvious ill effects, even after months or years of treatment. The apparent innocuousness of REM sleep deprivation contrasts markedly with the effects of total sleep deprivation (see earlier). The implication of these several findings is that we can get along without REM sleep, but need non-REM sleep in order to survive.
Several general hypotheses about dreams and REM sleep have been advanced. Francis Crick (of DNA fame) and Grahame Mitchison suggested that dreams act as an “unlearning” mechanism, whereby certain modes of neural activity are erased by random activation of cortical connections. The hypothesis is based on the idea that the human brain represents information by the activity of sets of neuronal networks that are widely distributed and overlapping. In computers, neural network architectures are subject to unwanted patterns of activity that can indeed degrade rather than enhance the information content of the system.
By analogy, these “parasitic” modes of activity might be unwanted thoughts or erroneous information, which, if not expunged, could become the basis for obsession, paranoia, or other pathologies of thought that prevent the “system” from working as efficiently as it should. In a different vein, Michel Jouvet proposed that dreaming reinforces behaviors not commonly encountered during the awake state (aggression, fearful situations) by rehearsing them while dreaming. Yet another hypothesis is that REM sleep and dreams are involved in the transfer of memories between the hippocampus and neocortex. Finally, it has been suggested that dreaming is simply an incidental consequence of REM sleep. None of these ideas are generally accepted.
In short, the questions of why we have REM sleep and why we dream remain unanswered, as are questions about consciousness per se (Box D).
Box D
Consciousness.
Why REM Sleep and Dreams Are Important for Health
Doctors have warned for years that Americans are not getting enough sleep, with health consequences ranging from drowsy driving and irritability to an increased risk of dementia, heart disease and early death.
Now, a recent study suggests that one particular type of sleep may be especially important when it comes to how the brain responds to stressful situations.
The research, published in the Journal of Neuroscience, found that people who spent more time in rapid-eye-movement (REM) sleep — the phase when dreaming occurs — had lower fear-related brain activity when they were given mild electric shocks the next day. The findings suggest that getting sufficient REM sleep prior to fearful experiences may make a person less prone to developing post-traumatic stress disorder (PTSD), the authors hypothesize.
The study isn’t the first to suggest that REM sleep delivers unique benefits. Some experts even believe that it’s actually a lack of REM sleep and a lack of dreaming — rather than just poor sleep in general — that’s responsible for many of the health problems Americans suffer from today. Here’s what scientists know so far — and what they suspect — about REM sleep, dreams and what happens when people are deprived of both.
What happens during REM sleep?
Sleep involves five distinct phases, which the brain and body cycle through several times during the night. The first four phases involve a transition from shallow to deep sleep, while the fifth phase, REM sleep, involves heightened brain activity and vivid dreams.
REM sleep stages tend to be relatively short during the first two-thirds of the night as the body prioritizes deeper, slow-wave sleep. And because longer periods of REM sleep only happen during the final hours of sleep (in the early morning, for most people), it can get cut off when you don’t spend a full seven or eight hours in bed, says psychologist Rubin Naiman, a sleep and dream specialist at the University of Arizona Center for Integrative Medicine and the author of a recent review about dreaming published in the Annals of the New York Academy of Sciences.
During REM sleep, there is more activity in the visual, motor, emotional and autobiographical memory regions of the brain, says Matthew Walker, professor of psychology at the University of California, Berkeley and author of the new book Why We Sleep.
But there is also decreased activity in other regions, like the one involved in rational thought — hence the reason for extremely lucid, but often nonsensical, dreams. (The dreams you remember when you wake up are only part of REM sleep, says Walker; in reality, the brain is highly active throughout the entire phase.)
Scientists are divided as to whether dreams are simply a product of random neurons firing during sleep, or if they’re something more — like a data dump that helps the brain separate important memories from non-important ones, or a way for people to prepare for challenges and play through different scenarios in their heads.
Naiman describes the brain during REM sleep as a sort of “second gut” that digests all of the information gathered that day. “Everything we see, every conversation we have, is chewed on and swallowed and filtered through while we dream, and either excreted or assimilated,” he says.
What are the health benefits of REM sleep?Several studies in recent years have suggested that REM sleep can affect how accurately people can read emotions and process external stimuli.
Walker’s research, for example, has demonstrated that people who achieved REM sleep during a nap were better able to judge facial expressions afterward than those who’d napped without reaching REM.
Walker and his colleagues have also found that people who view emotional images before getting a good night’s sleep are less likely to have strong reactions to the same images the next day, compared to those who didn’t sleep well. “I think of dreaming as overnight therapy,” Walker says. “It provides a nocturnal soothing balm that takes the short edges off of our emotional experiences so we feel better the next day.”
Adding to that research, the most recent study — from researchers at Rutgers University — suggests that the quality of a person’s sleep before a traumatic event can play a role in how the brain reacts to a scary situation. “The more REM, the weaker the fear-related effect,” the authors write in their paper.
Researchers aren’t certain why this happens. But the part of the brain that secretes norepinephrine during wakefulness and non-REM sleep takes a break during REM sleep.
“Norepinephrine is associated with stress, and it affects the degree to which the amygdala — the fear center of the brain — is sensitive to stimuli,” says Itamar Lerner, co-author of the new paper and a postdoctoral sleep researcher at Rutgers University.
MORE: How Dream Therapy Can Change Your Life
One theory, known as the REM calibration hypothesis, holds that norepinephrine builds up during the day and can be reset to normal levels during REM sleep. “When that happens, we believe that the amygdala may become less sensitive to stimuli, and less likely to overreact to something that really shouldn’t be fearful,” says Lerner.
Other studies have suggested that REM sleep may be important for other reasons, but there’s less evidence of direct, REM-specific benefits in these areas. In his recent review, Naiman writes that dreaming has effects on memory and mood, and cites research linking poor-quality REM sleep to conditions like Alzheimer’s disease and depression.
(It’s worth noting that these studies only prove associations — not whether one problem actually causes or contributes to the other.)
Walker, too, believes that dreams and REM sleep have benefits — but he says it’s not the only stage of sleep that matters. In fact, he says, extensive evidence suggests that slow-wave, non-REM sleep “still seems to carry the majority of health benefits,” including regulating blood flow and blood glucose levels, and clearing Alzheimer’s-related plaque from the brain. “REM sleep may have its own function, but most of the research still focuses on the restorative and very important benefits of the other phases,” he says.
How to get more REM sleep
If you wake up every morning with vivid memories of last night’s dreams, chances are you’re getting at least some decent quality REM sleep, says Walker. But besides that there’s no easy way to monitor your levels for REM sleep specifically. Most consumer sleep trackers aren’t an accurate judge, says Lerner, and neither is how refreshed you feel when you wake up.
“For most people, REM sleep makes up about 20 to 25% of the time they spend asleep,” says Lerner’s co-author and research assistant, Shira Lupkin. “So for now, the best way we can recommend getting more REM sleep is to simply get more sleep overall.”
There are, however, some known culprits that disrupt normal sleep patterns and reduce total time spent in REM sleep. A big one is obstructive sleep apnea, a condition that interferes with nighttime breathing and causes people to wake up many times throughout the night. “Seeking help for a sleep disorder, like using a CPAP machine for sleep apnea, can help elevate REM efficiency back to relatively normal levels,” Lerner says.
Other aspects of modern life — including alcohol, drugs, nicotine, the use of artificial light at night and dependency on alarm clocks — interferes with REM sleep as well, Naiman writes in his review. “Routinely waking up with an alarm clock repeatedly shears off the endings of our most protracted REM/dream periods,” he writes.
“Imagine being abruptly ushered out of a movie theater whenever a film was nearing its conclusion.”
For better sleep overall, it helps to sleep in a cool, dark room and go to bed at the same time every night, Walker says. Practicing other aspects of good sleep hygiene — like powering down electronics and nixing the nightcap — may also help improve your sleep —and maybe even your dreams.
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REM and slow-wave sleep - what is the difference and which is more useful
Let's understand what REM and slow-wave sleep are and which one is more useful.
Ekaterina Aniskina
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Our sleep is divided into two phases: fast and slow. Together they form one sleep cycle, which is repeated during the night an average of five times. So what is the difference between fast sleep and slow sleep, which one is more useful and which time is better to wake up?
Non-REM sleep
Non-REM sleep accounts for 75% of total sleep time and is divided into three main stages.
The first stage is intermediate between wakefulness and falling asleep, when the body gradually sinks into sleep. Sometimes at this moment there are various manifestations of hypnagogia familiar to many, such as a sharp jerk with the legs. This happens because of the signals of the brain, which considers the relaxation of the body as a potential danger, and therefore tries to wake up the body. As a rule, about 60-70% of people face a similar phenomenon. Stress, increased caffeine intake and regular sleep deprivation are to blame. The sleep paralysis that bothers some people also occurs during the first stage of non-REM sleep. This stage of falling asleep lasts about 5-10 minutes, depending on the person's fatigue.
The second stage takes up half of the total sleep time. A person falls asleep, is no longer aware of what is happening around, the body temperature drops. The second stage continues for 20 minutes.
The third stage is the deepest sleep, during which the body is restored: growth hormones, testosterone and melatonin are produced, tissues regenerate and grow, the brain distills cerebrospinal fluid and removes decay products.
Human muscles relax, and blood flow to them increases. This is the most useful part of sleep, which is highly undesirable to interrupt. Insufficient daily deep sleep does not allow the body to rest and increases the risk of various diseases. In addition, it is at this stage that the brain structures memory and “turns” short-term memories and skills into long-term ones. In this state, a person remains for 30-40 minutes.
It is important to remember that with a lack of slow-wave sleep, the body's immunity decreases, brain activity slows down, it becomes more difficult to concentrate even on simple tasks, a person feels lethargic and anxious.
All this happens as a result of insufficient sleep, when you wake up on an alarm after only a few hours without sleeping the required number of cycles.
REM sleep
This phase makes up 20–25% of all sleep. For the first time during the night, a person falls into REM sleep every hour and a half after falling asleep.
With each sleep cycle, the REM phase becomes longer and the slow phase becomes shorter. Surely in the morning you yourself have noticed more than once that you wake up more often, faster and less unexpectedly. It is during REM sleep that we see dreams that we remember in the future. And if you watch a person from the side, you can see that his eyes move in different directions, sometimes people move their arms and legs, turn over. Moreover, all muscles, except for the oculomotor muscles, are as relaxed as possible. Interestingly, at this time, the body temperature can constantly change, then falling, then rising. It is better to wake up at this stage of sleep, and various mobile applications can help determine it.
Normal non-REM sleep lasts about 90 minutes. Then comes the phase of REM sleep lasting 10-20 minutes. Together they form a cycle of 100-120 minutes. For a proper rest of the body, it is necessary to oversleep five such cycles. However, each time their time will change: non-REM sleep will become shorter, and REM sleep will be longer.
how they differ and how to sleep better
Many have heard that sleep is divided into slow and fast phases, but not everyone knows what they are. Today we will talk about what fast and slow sleep means, what features each phase has and what significance they have for a person.
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The branch of medicine called somnology deals with the study of sleep. Somnologists analyze brain activity and physiological reactions during sleep using special devices. One of the leading methods is polysomnography - a comprehensive study of a patient's sleep, in which the equipment records the frequency and depth of breathing, muscle contractions, body position, transmission of nerve impulses, heart function and many other parameters. As a result, a hypnogram is obtained - a graph that reflects information about the structure of sleep, including its quality during the phases of REM and non-REM sleep.
Specialists have an effective tool with which it is easy to distinguish between REM and non-REM sleep - this is an electroencephalogram.
Without special devices, it is quite difficult to understand whether slow sleep or fast sleep. Most likely, if a person moves his arms or legs, he is in REM sleep. During non-REM sleep, body temperature drops, breathing slows down, and muscles relax.
REM sleep
REM sleep is the phase during which the information received during the day is processed. Studies have found that during REM sleep, brain activity is practically the same as during wakefulness. REM sleep is important for the formation of memories and the consolidation of skills.
REM sleep can be determined by eye movements and irregular breathing. A person in REM sleep can move his hands. Body temperature and heart rate during this period are unstable and can fluctuate from low to high values.
REM sleep normally takes 20-25% of the total sleep time. It comes about an hour and a half after falling asleep and then repeats every hour and a half, each time becoming longer.
Especially long REM sleep is observed in the morning hours.
Non-REM sleep
Non-REM sleep is the phase during which physiological rest and tissue regeneration occurs. It is at this time that the “recharging” of the brain, the structuring of memory takes place. A person in the non-REM sleep phase has a decrease in blood pressure and body temperature. Muscles are relaxed, breathing becomes rarer.
Normally, non-REM sleep takes up 75% of the total sleep time. It is divided into three stages, which scientists designate as N1, N2, N3.
N1 (light sleep) is a transitional stage between falling asleep and waking. During this phase of non-REM sleep, phenomena such as hypnagogic jerk (feeling of falling and startling when falling asleep), visual, auditory and tactile hallucinations, sleep paralysis, sleepwalking, sleep-talking can occur.
N2 - body temperature drops, muscles relax, a person completely disconnects from reality.
Normally, N2 slow-wave sleep takes up half the time of all sleep and occurs in segments of about 20 minutes.
N3 is a deep sleep during which blood pressure decreases and breathing becomes rare. At this stage, body tissues are restored, hormones are produced and metabolites are excreted. The brain, meanwhile, is engaged in "archiving" memories of events, moving them from short-term memory to long-term memory.
How to increase non-REM sleep
With a lack of non-REM sleep, the body's resistance decreases, immunity decreases and brain activity slows down. It is more difficult for you to concentrate even on familiar tasks, lethargy and anxiety appear. There may be malfunctions in the endocrine system and hormone production. A reduced phase of non-REM sleep also increases the risk of Alzheimer's disease, heart and vascular diseases. Obviously, in order to maintain health, it is necessary to maintain the normal duration of this sleep phase.
To increase the duration of non-REM sleep, it is important to follow a few rules.
- Scheduled sleep. Take care of your routine. Getting up and going to bed at the same time is definitely a healthy habit.
- Movement is life. During the day (just not before bedtime!) Move more. So the brain cells will receive more oxygen, and this will help to establish biological rhythms.
- Neither cold nor hot. Ensure that the temperature in the room is comfortable for sleeping. Ventilate the room regularly.
- Put the phone down. Gadgets have a bad effect on the quality of sleep. An hour and a half before leaving for Morpheus, put your smartphone away, do not watch TV and do not use a computer.
What is the difference between REM sleep and slow-wave sleep
The main difference between the phases of slow-wave and REM sleep of a person from each other is the difference in brain activity, which is vividly illustrated by the EEG.
REM sleep is characterized by frequent eye movements, and during non-REM sleep they are practically absent. The dreams we have during REM sleep are more likely to be remembered, although studies have shown that dreams occur during both phases.
Why slow-wave sleep is better than fast sleep
Both slow-wave and REM sleep are important for the normal functioning of body systems. It is believed that the phase of non-REM sleep is more significant for recovery. By waking up a person at this time, we will deprive his brain of the opportunity to "reboot". In addition to the general poor state of health of the sleepy, impaired concentration, increased nervousness, lethargy, apathy, and irritability await. And if such deprivation of slow-wave sleep occurs regularly, there are high chances of encountering serious mental disorders. It is better to wake up in REM sleep. By the way, numerous applications for gadgets can help with this.
However, one should not think that REM sleep is useless and can be sacrificed without consequences. This phase prepares all body systems for awakening and includes the connection between the physiological processes in the brain and consciousness.
Slow-wave and REM sleep: the norm
For an average person, the norm of slow-wave sleep is 70%, and REM, respectively, 30% of the total night's rest. The total duration of sleep sufficient for recovery is 7-9hours per day.
NREM sleep should normally last about 90 minutes. It is followed by a phase of REM sleep lasting 10-20 minutes. These two stages together form a cycle that a healthy person usually repeats 5 times a night. The phases of non-REM and REM sleep are unevenly distributed. So, for the first time after falling asleep, the REM sleep phase lasts about 5 minutes, and closer to awakening, its duration reaches 60 minutes.
