All animals do it. Whether reptile, bird, insect, or mammal we all have one thing in common: We all sleep. But what is it about laying still, closing your eyes, and resting your mind that makes such a difference day-to-day?

t’s considered the cure for all kinds of aliments: the common cold, indecision, forgetfulness. The phrase used over and over again: Sleep on it. Sleep deprivation makes people angry, the body ache, and logical thinking becomes more difficult after a fitful night’s sleep. Scientists have studied brain activity during the sleep of various animals and have discovered that the brain is far from restful during the nighttime hours.

How We Sleep

In 1972, Nobel Prize-winning doctor Sir John Eccles presented a tape of quick, sharp static-like noise to a class of medical students. On a recent episode of National Public Radio’s RadioLab, Dr. Carlos Schenck author of Paradox Lost: Midnight in the Battleground of Sleep and Dreams explained that the noise – the rapidly firing static – was actually the sound of a cat´s brain while asleep.

This research defied commonly held belief that the brain is restful during sleep. In fact, it’s very active.

In studying animals, scientists have discovered that some creatures sleep unihemispherically – letting only one half of their minds rest at a time – while other animals are able to sleep letting both sides of the brain relax at the same time.

Animals that only allow one side of their brain to rest at a time include waterborne mammals, like dolphins, whales, which need to be awake to consciously breath. Other animals, like birds and lizards also sleep unihemispherically, often sleeping with one eye open, to watch for predators that would want to eat them.

Humans and other terrestrial animals – other animals that live on land – are not able to sleep this way, because they seek refuge when sleeping where predators are not a threat. Because of this, we have evolved to only sleep with both sides of the brain asleep at the same time.

People who suffer from night terrors or sleepwalk are believed by scientists to be overly sensitive of “predation risk” – the risk of being attacked by another animal the way ducks or lizards are aware of predators.

 

Why do we sometimes feel tired?

Many important connections we make in life become clearer after a good night’s rest. Dr. Allan Pack at the University of Pennsylvania believes that during sleep our bodies are able to sweep our cells of proteins that are unable to be used. When we miss sleep, the body is unable to sweep our cells of these toxic proteins, making us tired.

 

How Sleep Helps Us Remember

Dr. Gulio Tunoni, a professor of psychiatry, said that he believes over 1,000 waves of electrical activity sweep over the brain during the night. All your memories of the previous day become a bit duller because this electricity reduces the connection between all memories. The small things a person learned and remembered during the day, like buying groceries and walking the dog are reduced. Because they were brief, they are reduced to almost nothing and make the mind quieter, and important memories seem clearer.

Dreams

Scientists from MIT put rats in a maze during the day, and listened to the sound of the animals’ brain cells communicating while they tried to solve the pattern of the maze. When the rats were in deep sleep at night, the same sounds of the rat running maze were present. The rats dreamt about running the same maze. In dreams the animals would try new possibilities to solve the problems of their waking life.

People who study the brain and sleep believe that our minds mark important events during the day so that the brain can revisit these problems during our sleep and try new solutions that we may not have considered during the day.

Other scientists have tested the idea of problem solving during sleep by giving a set of people the video game Tetris. Over 60 percent of people reported dreaming of images associated with the game. To researchers this proved that dreams are a way of reinforcing learning, according to a 2000 article in Scientific American.

One of the most famous examples of the mind solving problems in sleep is that of German chemist August Kekule. While trying to determine the shape of the molecular benzene ring, Kekule dreamt of a snake biting its tail. Legend says that this dream inspired his discovery of the circular shape of benzene. Kekule went on to become one of the most important figures in organic chemistry.

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