“To sleep, perchance to dream. Aye, there’s the rub . . . “

Aye, there’s the rub indeed–the rub being, nobody’s really sure why we sleep. Or why we dream. Or why either is important.

Some scientists doubt that dreaming is of any great importance. They don’t have those doubts about sleep.

We know sleep is important because everybody’s doing it–not just every human, but every bird, fish, reptile and mammal.

We know sleep is important because, like it or not, we’re going to spend a third of our lives immersed in it.

We know sleep is important because, if we don’t sleep, we die. That makes it rank right up there with food and water and air.

And even if we don’t exactly know what sleep is, or what it’s for, we do know a lot of what happens when we sleep, thanks to innumerable unsung heroes, mostly university students, who have bravely volunteered to go into a laboratory and–sleep. (I’ve often wished somebody on my college campus had been conducting sleep research…)

Determining what happens when someone is asleep obviously depends on more than just watching them snore, although even from that we have learned that on average we move 40 to 60 times a night–a good thing, since otherwise we could cut off the blood supply to a limb by lying on it and cause permanent damage. However, for more detailed information on sleep, we need to see what’s happening inside the brain itself.

Fortunately, in 1924 Hans Berger decided to paste two small pieces of silver foil to his 15-year-old son’s scalp, attach wires to them and connect the wires to a galvanometer, which measures electrical current. That was the forerunner of the electroencephalograph.

He dubbed the regular electrical signals he received from his son’s brain alpha waves, which show that the brain is calm and relaxed. These waves occur seven to 12 times per second, and we go through this stage as a precursor to sleep.

Next comes a stage of light sleep, during which we produce theta waves, at only three to seven cycles per second, with a low amplitude. These are interrupted by frequent bursts of activity called sleep spindles, at 12 to 15 cycles per second.

Next comes a period of regular, high-amplitude delta waves at only one to two cycles per second, with a few sleep spindles. Finally sleep deepens to the point that the brain produces wave patterns similar to those occurring in a coma, at one to three cycles per second.

And then our brain suddenly erupts with activity, similar to the waking state. Our eyes move rapidly under our closed eyelids, our heart rate, breathing rate and blood pressure, which have dropped with our body temperature as we fell asleep, all go up, and we dream.

(Fortunately, despite all this activity, our body remains effectively paralyzed–otherwise we might act out our dreams, which, if you’ll recall a few of your more vivid sleep-time experiences, could be embarrassing, if not downright dangerous.)

This stage is sometimes called paradoxical sleep, because even though are brains are active, we’re not awake. It’s also called REM sleep, REM standing for rapid eye movement. This stage lasts from 10 minutes to half an hour, generally lengthening as the night progresses. All these stages occur in a regular 90-minute cycle, usually four to six times a night.

Babies are in REM sleep fully half of their sleeping time, which is already much longer than ours (a newborn sleeps up to 16 hours a day, a one-year-old around 13), while adults usually have one or two hours of REM sleep a night. If we don’t get enough REM sleep, our bodies make up for it by longer-than-usual periods of REM sleep during our next sleep or next several sleeps, which suggests we need sleep for the REM activity specifically, and not just to rest weary bodies and minds.

Unfortunately, as with so much else about sleep, nobody’s really sure why that should be so. Some scientists suggest that, in infants, REM sleep helps establish the pathways between our nerves and muscles that enable us to move our eyes. It may also help establish the functional structures in the brain involved in, for example, learning to walk.

In adults, it may help in maintaining mood and emotion, or perhaps it’s required for storing memories and fitting recent experiences into the larger framework of our personality.

Dreaming seems to be an integral part of REM sleep, but there’s great debate on whether it is vital to our well-being or just an interesting side-effect of our brain chemistry.

Psychological theories place great importance on it as a kind of rearranging of the mental furniture that is part of our coping with the stresses of life; those who focus on the “hardware” of the brain are less sure. As Dr. J. Allan Hobson, a professor of psychiatry at Harvard Medical School, puts it, “If it’s critical, why do so few people remember their dreams?”

On the other hand, Robert P. Vertes, a neuroscientist at Florida Atlantic University, figures we dream because otherwise we might, during the coma-like deepest stage of sleep, lose consciousness permanently and die.

Whether dreaming is important or not, sleeping certainly is. In fact, you can survive longer without eating than you can without sleeping. Hunger strikers have lived up to 60 days without food, but in just a few days without sleep humans begin to experience anxiety and hallucinations, eventually ending in a coma and even death.

One thing is certain: all of us will continue, more or less once a day, to lie down somewhere and let our minds and bodies shut down.

And even if we never do fully understand why–well, it’s nothing to lose sleep over.

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