The Science of Sleeping

Like food, water and oxygen, sleep is a vital part of the way the human body functions to ensure survival. So, as we drift off to sleep every night, what actually happens to our body during sleeping hours, and why is it so important for every day function?

While doctors are stumped as to the biological purpose of sleep, they do know that sleep benefits brain function, mood and overall mental and physical health.

According to Dr. Harly Greenberg, chief of the Division of Pulmonary Critical Care & Sleep Medicine at Northwell Health’s Long Island Jewish Medical Center and North Shore University Hospital, sleep is an active process that restores and rejuvenates brain function for the next day.

This video explains the process of brain activity while we sleep.

For much of the 20th century, scientists believed that sleep was a passive process, but American psychologist Nathaniel Kleitman and his partner Eugene Aserinsky discovered the active nature of the REM sleep cycle in the brain.

Non-REM sleep is a lighter stage of sleep, where the body transitions from wakefulness to sleep by cooling body temperature, slowing breathing and relaxing the muscles. The REM sleep stage is the active stage called “rapid eye movement,” where brain activity is heightened, and the eyes move quickly from side to side. This is also the stage of sleep where we dream the most.

While it may seem strange to think that our brain is awake while we sleep, it is imperative for health that brain activity continues.

Greenberg said that ongoing research is being done about processes occurring in the brain during sleep, one being "synaptic homeostasis." This is where the brain discards weak synapses to create space for new ones to form the next day.

Think of this process like a computer. A computer’s hard drive can only store so much information, from apps to music to photos and everything in between. When there is limited storage, we start deleting all the things we do not need or use to make room for newer downloads.

Part of the homeostatic process also involves consolidating and storing short-term memories in the hippocampus and long-term memories in the cortex.

According to Greenberg, patients who were given a proper night of sleep and given a test the next day tested better than those who had a poor night of sleep.

Photo courtesy of Nguyen Dang Hoang Nhu from Unsplash

Photo courtesy of Nguyen Dang Hoang Nhu from Unsplash

A study done by the Journal of Sleep Research tested 11 sleep deprived subjects against 11 control subjects and found that sleep deprivation significantly impaired the subject’s testing ability due to poor performance from the prefrontal cortex.

“And if you look at the profiles of genes that are transcribed within the neurons in the brain, about a third of the genes have differential expression between wakefulness and sleep,” said Greenberg. “So, I think the ‘all-nighter’ to study before an exam is just the absolute wrong thing to do.”

Synapses being discarded from the brain while we sleep.

Ongoing research has also found ties between energy, metabolism and sleep. During sleep, the brain’s neurons get rid of “metabolic waste” and regenerate cellular function to promote better energy for the next day.

“So we've also learned that prolonged wakefulness increases the production of metabolic byproducts and proteins that could be damaging to the brain, such as amyloid protein,” Greenberg said. “And sleep is one of the times that these proteins are cleared from the brain."

There is a lot of what Greenberg calls “cellular housekeeping functions” that goes on during sleep. The sleep needed for these housekeeping functions to perform, however, varies between different age groups.

Courtesy of Andrea Piacquadio via Pexels

Data from Nathaniel Kleitman's *Sleep and Wakefulness*

Data from Nathaniel Kleitman's *Sleep and Wakefulness*

The mean number of hours of sleep for a person to have each night throughout their lifetime is eight, according to Kleitman’s work, Sleep and Wakefulness. This number changes depending on age, where infants can have upwards of 15 hours of sleep, while adults can have as low as five and still have sound cognitive function. Kleitman bases the number of hours of sleep on, “an increased ability to remain awake” as we develop and mature over time.

Google Form survey with 40 respondents on average hours of sleep.

Google Form survey with 40 respondents on average hours of sleep.

After 40 people between the ages of 18-25 responded to a survey sent through Twitter and Instagram, 80% said they got five to eight hours of sleep on average every night; however, 63% felt that they still did not get enough sleep.

When asked what affected their sleep habits, one person surveyed said, “University affects sleeping habits greatly; depending on workload, having a job and keeping up with social life/clubs, it is hard to create a consistent sleep schedule.”

Courtesy of Laura James via Pexels

Greenberg says he finds that people feel much more tired in the morning when they work against their circadian rhythm, which is the biological clock that tells us when to go to sleep and when to wake up.

For example, "it's people who have rotating shift work, night shift work, people who go from nights to evenings to days where their work causes sleep times to vary and they're sleeping outside of their circadian or biologic window for sleep,” Greenberg said.

People with major varying sleep patterns, called “circadian misalignment,” are often sleep deprived and are more prone to developing diseases like diabetes, cardiovascular disease and even cancer, according to Greenberg.

Including treatment for shift workers, research in sleep medicine is constantly underway for experts in the field.

“What we have been focusing on quite a bit now is work that relates to understanding the functions of different areas of the brain during sleep and what they do and the parts of the brain that regulate both sleep and wakefulness and how these areas interact,” said Greenberg.

Greenberg added that, “The field of sleep medicine is an important and growing field that can assess people for sleep disorders that interfere with their sleep and make their sleep non-restorative and can affect daytime function.”

There are a range of disorders that medical researchers have identified and are building on treatments for, such as:

Insomnia- having trouble falling and staying asleep

Sleep apnea- trouble breathing during sleep

Narcolepsy- a form of hypersomnia, being unable to stay awake during the day

Parasomnia- unusual actions during sleep, like walking, talking and eating

While many of these disorders need to be medically identified and diagnosed, there are recommendations for people who have trouble sleeping and what they can do at home.

Greenberg recommends that people start prioritizing sleep. Keep a regular bedtime and wake time, and try to wind down half an hour before bed.

“If you have trouble falling asleep, the worst thing you can do is try harder to sleep,” Greenberg said. “So you should not be in bed for longer than 20 to 30 minutes without sleeping, because you begin to develop subconscious associations of the bed and bedroom environment with the frustrating inability to sleep.”

Greenberg calls this “stimulus control recommendation,” which includes avoiding doing activities in bed that can be associated with heightened alertness, such as doing work in bed.

“If you can't sleep, give it 20 to 30 minutes,” Greenberg added. “If not, then leave a bed and bedroom, do something relaxing in another part of the house. And then when you feel sleepy, you go back to bed and still maintain that regular bedtime and awakening time.”

Courtesy of Acharaporn Kamornboonyarush via Pexels

The Science of Sleeping

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