REM sleep makes the brain solve problems and create memories – 07/03/2023 – Equilibrium

Any device that monitors your sleep will show you that sleep is far from passive. And no stage of sleep demonstrates this better than the stage characterized by rapid eye movement (REM), also known as the dream stage.

“REM sleep is also called paradoxical sleep or active sleep because it’s actually very close to the waking state,” says Rajkumar Dasgupta, an expert in sleep and pulmonary medicine at the University of Southern California’s Keck School of Medicine.

Before scientists discovered REM sleep in the 1950s, it wasn’t clear that anything really big was happening to the brain at night. Today, however, scientists understand sleep as a highly active process made up of very different types of rest — including the dream phase, which in some ways doesn’t feel like rest at all.

The body is normally “off” during the period, but the brain is very “on”. It is generating vivid dreams and synthesizing memories and knowledge. Scientists are still trying to better understand how this strange state of consciousness works.

“It goes without saying that there’s still a lot to discover about REM sleep,” says Dasgupta. But from what scientists already understand, this period is critical for our emotional health and brain function — and potentially even our longevity.

When does REM sleep occur?

“We go in and out of a rhythmic, symphonic pattern of various sleep phases throughout the night: not REM 1, 2, and 3, and REM,” points out Rebecca Robbins, instructor of medicine at Harvard Medical School and scientist in the Division of Disorders. of sleep and circadians at Brigham and Women’s Hospital.

When we nap, we enter the first stage of non-REM sleep. This lasts less than ten minutes and is considered a light sleep. Breathing and heart rate slow down and muscles relax as we enter the second stage of non-REM sleep, in which body temperature drops and brain waves slow down. Then we enter the third stage, known as deep sleep, where the body repairs bones and muscles, strengthens the immune system, releases hormones, and restores our energy.

After that, REM sleep begins, in which heart rate, breathing and brain activity increase. Brain regions involved in processing emotions and sensory stimuli (from the dream world) become activated. At the same time, the brain paralyzes the muscles in the arms and legs to prevent us from putting our dreams into practice, explains Dasgupta.

Ideally, the person goes through the four steps in cycles of 90 to 110 minutes in length that are repeated four to six times in a typical night. So after the last REM cycle, she wakes up feeling rested and alert, says Indira Gurubhagavatula, a sleep specialist at Penn Medicine and professor of medicine at the VA Medical Center in Philadelphia.

What are the benefits?

If you’ve ever gone to bed upset about something and woke up feeling noticeably less upset, it’s probably due to the emotional processing and reconsolidation of memories that occur during REM sleep.

There’s evidence that our brains separate memories from their emotional charge — removing the “sharp, painful edges” of life’s difficulties, says Matthew Walker, professor of neuroscience and psychology and founder and director of the Center for Human Sleep Science at the University of California. California at Berkeley. For him, REM sleep “is like a form of therapy done overnight.”

The period also facilitates learning. During this phase of sleep, the brain strengthens neural connections formed by the previous day’s experiences and integrates them into existing networks, says Robbins.

Walker adds, “We take this new information and start checking it against our catalog of stored information. It’s almost a form of information alchemy.”

These newly created connections also make us more creative, he says. “We wake up with a revised mental network of associations” that helps us find solutions to problems. Researchers in Walker’s lab conducted a small study in which people were awakened from different stages of sleep and instructed to unscramble anagrams. They found that people awakened when they were in REM sleep solved 32% more anagrams than people interrupted during non-REM sleep.

And there are dreams, of course: most of our vivid dreams occur during this period. Some experts think that dreams are nothing more than a by-product of REM sleep – the mental manifestation of neurological work. But others believe they can help people process painful experiences, Walker says.

And while most physical processes, such as repairing bone and muscle tissue, happen during non-REM sleep, some hormonal changes occur when you’re dreaming, Walker points out, such as the release of testosterone ( which peaks at the beginning of the first REM cycle).

What happens if we don’t reach REM enough?

Genetics and other factors can influence how much sleep each person needs, but according to Gurubhagavatula, most adults should aim for seven to nine hours of sleep a day, which includes about two hours of REM sleep.

People generally need fewer hours of sleep as they get older, including slightly less sleep time. But large REM deficits, no matter at what age, can deprive a person of the psychological benefits of the period, says Dasgupta. The person may have more difficulty learning, processing emotional experiences, and solving problems.

Dysregulated REM sleep is also linked to cognitive and mental health issues, such as slower thinking and depression, says Ana Krieger, medical director of the Center for Sleep Medicine at Weill Cornell Medicine. Insufficient, fragmented REM sleep and REM sleep behavior disorder — in which muscle paralysis fails to occur and people manifest their dreams physically, often with kicks or punches — are linked to neurological problems ranging from mild forgetfulness to dementia and Parkinson’s disease.

A 2020 study of more than 4,000 middle-aged and older adults found that every 5% reduction in REM sleep is linked to a 13% higher risk of death from any cause over the next two decades. Lack of sleep is generally associated with death, but research suggests that sleep phase failure “is the biggest single factor of all stages,” Walker says.

He and other experts don’t fully understand the relationship between REM sleep and mortality. “I think we still don’t have a sufficient understanding of REM sleep to be able to definitively state which mechanisms are involved”, he points out. Or, as Gurubhagavatula puts it, whether lack of REM sleep actually causes death.

How do you know if you need more REM?

For Gurubhagavatula, it is difficult to distinguish the signs of sleep deprivation from signs of sleep deprivation in general. If you don’t sleep as much as you need, you’re probably suffering from insufficient REM.

But certain behaviors can specifically compromise the dream phase. “Reducing your sleep time by going to bed late and using an alarm clock to wake up can increase the risk of chronic REM sleep deprivation,” says Gurubhagavatula. This is because the phase’s longest periods often occur towards the end of the night.

Consuming alcohol before bed is another thing that clearly impairs REM, says Walker, because the process of metabolizing alcohol produces compounds that affect the regulation of the sleep cycle. What’s more, as Gurubhagavatula shows, people whose alcohol consumption is moderate or heavy are at increased risk for REM sleep behavior disorder.

Antidepressants can also reduce this phase or trigger REM sleep behavior disorder. And specific health conditions — such as narcolepsy, obstructive sleep apnea and depression — can raise the risk of dream phase abnormalities, Dasgupta says. If you have one of these issues and you’re feeling like you’re not getting enough sleep, see a sleep doctor. In the case of sleep apnea, for example, says Dasgupta, “as soon as we start treatment people often start to have more REM.”

Is it possible to prioritize REM sleep?

While recent research suggests that people may have a little more REM in the winter, the idea that it’s possible to improve a specific sleep phase is a modern myth. “People want to manipulate sleep and have more than one specific stage, but the body doesn’t work that way,” says Krieger. The natural architecture of sleep is not something we should try to mess with, but something that should be protected.

“To get healthy REM sleep, you need to focus on healthy sleep as a whole and let your brain do the rest,” says Gurubhagavatula.

Waking up and going to bed at the same time each day helps the brain and body know when to rest, and that makes for more efficient sleep, Robbins points out. Other behaviors that help regulate the body clock include eating at regular times and not eating late at night, exercising regularly, getting some sun in the morning and avoiding blue light – from electronic devices – at night.

Gurubhavatula recommends following other positive sleep practices, such as avoiding alcohol and stimulants like caffeine and nicotine (especially later in the day) and sleeping in a dark, quiet, and cool environment. And don’t forget the importance of a relaxation routine to help you transition from action to a night of rest and recovery — including the strangely busy time the brain spends during REM sleep.

Translated by Clara Allain