Abstracted from A Scientists View of Almost Everything By Mark M Green

When you or any animal sleeps there’s no doubt of the increased danger from enemies or predators. Sleep means vulnerability. Sleep also means less time to get things done. So why sleep?

What is sleep? For a wide range of animals, from human beings down to worms and insects, sleep is subject to a circadian rhythm. Circadian comes from the Latin, circa for around and diem for day and describes the changes in living organisms as the day progresses. We become tired in the night and awake with the sun. This is our rhythm and imposed on this rhythm is sleep homeostasis, which is the term biologists use to describe the requirement for a certain amount of sleep—approximately 12 hours for a fruit fly, eight hours for adult humans, rats 14 hours, elephants about three hours.

There are some ideas about these differences but science offers no certain answers. Sleep homeostasis is connected to what is called sleep debt. If you don’t get enough sleep at night, then you need to make it up to feel okay. But just sleeping your usual normal amount the next night is not enough.

What do we know? The invention of a machine, the electroencephalograph (EEG) was critically important in understanding that sleep is an entirely different state from waking and that there are different stages of sleep, those in which there is rapid eye movement (REM) and not (NREM). The brains of mammals give off very weak electrical signals, detected by the EEG machine, which are characterized by wave patterns. With these kinds of measurement scientists can determine that we pass through various stages of sleep. While the NREM sleep is signaled in the EEG machine by slow regular wave patterns, the EEG machine shows that the electrical signal of REM sleep is similar to being awake. Dreams occur during REM sleep, which is thought to account for the wake-like electrical signals although other biological mechanisms during REM sleep keep us from acting physically on these dreams, which our sleeping partners might be grateful for.

I don’t know about the dreams of a fruit fly but we and fruit flies share many similarities. Like us, caffeine and amphetamines keep flies awake; younger ones sleep most—elderly sleep least; antihistamines put them to sleep. When scientists found they could alter a gene in these flies and in mice as well, which substantially removed the need for sleep they immediately figured that we probably have a similar gene. But don’t run to your gene removal specialist so quickly—the sleepless flies had half the lifespan of their sacked out brethren.

Medical science shows that not sleeping is unhealthy for humans as well, and in a serious way. Rats are biologically like us in many ways, but need more sleep than we do; when deprived of sleep for two weeks, they deteriorate and die. Studies on rats show that genes involved in building connections between neurons in the brain are turned on only during sleep, causing one scientist to write that “sleep takes parts of the nervous system offline for maintenance.” Research on zebra fish and roundworms shows that certain body parts are constructed during sleep supporting this maintenance hypothesis.

There seems to be a connection between sleep and memory. Experiments show that people better remember something by taking a nap after learning. There’s evidence that during sleep better connections are made between short term and long term memory. A sleep researcher at Boston University published the results of an experiment in which a group of rats that were taught how to avoid a mild electrical shock spent far more time in REM sleep than a group of rats that were not taught how to avoid the same shock.

Finally, much is being learned about the connection between our body’s chemistry and sleep. Prolonged wakefulness increases the amount of adenosine in the body, which then makes us feel sleepy. Adenosine is an important component of our energy yielding mechanisms, which are harder at work when we are awake. Science finds it significant that the chemical structures of adenosine and caffeine are similar enough that some biochemical sites can accept caffeine, which then block the action of adenosine: this is thought to be the reason for the effect of caffeine. And finally there is melatonin, which is produced only when we sleep, and only when it is dark, a chemical that is thought to be responsible for keeping us healthy in several important ways. Add to the chemistry insight into sleep, recent research demonstrating that sleep, specifically NREM sleep, activates the glymphatic system in the brain, which removes debris formed in the brain’s activities when awake. Some of this debris appears to be associated with the formation of misfolded proteins contributing to dementia increasingly associated with aging.

Sleep, according to Shakespeare: “Balm of hurt minds, great nature’s second course,” continues to be an unfolding mystery to science.

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