In this blog, I am going to deal with a question that has stumped some of the most talented researchers in the world. That should hopefully get your attention- this vexing question seems simple, but represents the “holy grail” of biology. The question: why do we sleep? Consider this- we spend approximately one-third of lives doing it and scientists are still not quit sure why. (Much of this and future blogs on this topic are adapted from a review article by Dr. Jerome Seigel in Scientific American.)
We can all understand why we need to breathe, eat, and drink. We need to get nourishment to maintain our ability to do things and we breathe to inhale oxygen and exhale carbon dioxide. There are also obvious needs for reproduction to maintain species, but when we think it about, sleep seems to be a counterintuitive biological process. The most simple answer forces us into a sort of logical circle of reasoning- we sleep because we would not be able stay awake and alert without it. That may be true, but that doesn’t really explain the “why” of sleep and what it accomplishes for us. As one researcher put it- we wouldn’t suggest that we eat because otherwise we would be hungry, nor would we say that we breathe to avoid feeling suffocated.
All mammals, birds, and reptiles sleep. For animals especially it would seem biologically that they didn’t sleep, because sleep but them at a great disadvantage. During sleep time, they are most exposed to the dangers of predators and are, at least seemingly, not engaging in activity that they require to keep themselves (or species) alive, like searching for food and water, protecting the young, or reproducing.
The study of sleep is still relatively young. For many years it was assumed that sleep was just a complete disconnection from the world without any significant brain function. That was until 1953, when research student Eugene Aserinsky connected an electroencephalograph or EEG (brain wave machine) to study his 8 year old son, Armond’s sleeping pattern. He also attached the machine’s wires to his son’s eyelids to determine when he woke up. To his surprise he found that Armond’s eyes were moving rapidly suggesting that he was awake, but he was actually still asleep. Aserinsky and sleep researcher Nathaniel Kleitman published their findings in the journal Science. This of course, became known as rapid eye movement, or REM sleep. This was the first sign that more was really going on in the brain during sleep than previously believed.
Let’s take a step back and contrast what happens in the brain and in the body systems during wake, non- REM sleep, and REM sleep to give us a better understanding of what some current scientists suggest may be happening during these different stages of sleep.
As you would expect, during wake the activity of the nerve cells or neurons in the brain are highly active. For the most part, during non-REM sleep, particularly during the stage known as delta or slow wave sleep, the brain’s activity ebbs and the body’s metabolism tends to be at its lowest point. With the decreased brain activity, vivid dreams are. (The exception to this pattern is a small group of neurons that that are most active during non-REM sleep. These cells are believed to be “sleep-on” neurons, which are the nerve cells responsible for inducing sleep.)