Zzzzz....

I wonder how many of you will have yawned by the time you get to the end of this entry. Not because it’s boring (I hope!), but because of the power of suggestion. The topic?

Sleep.

Sleep is a part of life - at least, it is if you are a mammal, reptile or bird. Like it or not, your brain needs to sleep. A sleeping person is a funny thing to watch. Someone who is asleep is usually lying down, eyes closed, and they are unresponsive to most soft noises. Their breathing is slow and steady, and their muscles are completely relaxed, though they will move around from time to time (usually once or twice an hour). In short, they are completely detached from most of the things happening in their surroundings – though they can be aroused with a strong enough stimulus.

Let’s delve into what happens to our brains and our bodies when we sleep. Human sleep architecture follows an oscillating cycle of REM (rapid eye movement) and NREM sleep (non rapid eye movement). REM sleep usually accounts for 25% of our slumber, with NREM making up the rest. In REM sleep, the brain is active while the body is inactive; NREM sleep is the opposite, with the brain being inactive and the body being active. The cycle usually lasts around 90 minutes, and it goes as follows:
NREM stage 1 (light sleep): you are somewhere between waking and sleeping
NREM stage 2 (sleep onset): you become disengaged from your surroundings, and your body temperature drops
NREM stage 3 and 4 (deep, restorative sleep): breathing slows down, blood pressure drops, muscles relax, hormones are released, and most tissue growth and repair occurs
REM sleep (dream sleep): eyes dart rapidly back and forth, muscles become immobile and stiff, brainwaves speed up to awake levels, and dreams occur
So when you fall asleep, your brain will pass through NREM stages 1 through 4, and then enter REM about 90 minutes after. REM sleep usually lasts from 5 to 30 minutes, and then you repeat the cycle every hour and a half. During NREM sleep, your body will unconsciously move around, turning over and rearranging itself. This is your body’s way of making sure that no part of your skin or body has its circulation decreased for too long a period of time.

That’s what sleep is – but why do we need it, anyway? In short, we don’t really know. Scientists have shown that sleep is essential for survival, but no one has the definitive answer of why. Evidence indicates that enough sleep is essential for a healthy immune and endocrine system, tissue repair, and may play a role in diseases such as hypertension, obesity and diabetes. It also seems to be important in higher cognitive functions. People who are sleep deprived have decreased memory and attention, complex thoughts, motor responses and emotional control. In fact, people who are sleep deprived sometimes function more poorly on tests measuring motor control and coordination than someone who is legally drunk.

As I mentioned before, sleeping is a part of life for all mammals, not just humans. If you have pets, it might seem like your furry friends do nothing but sleep! Dogs sleep somewhere between 13 and 18 hours each day, while cats clock in an average of 16-20 hours a day. (That equates to about two-thirds of their lives, by the way.) Koala bears manage at least 19 hours of shut-eye each day. However, even koalas are not the sleepiest mammal around – that record belongs to armadillos, opossums and sloths. They sleep an average of 80% of their lives (almost 20 hours every day). That’s a lot of time slumbering! Water-bound mammals, such as whales and dolphins, have slightly different requirements for sleep. They are conscious breathers (they actively decide when to breathe, unlike humans, who breathe without thinking about it), so they have to remain at least partially conscious to stay alive. Because of this, only half of their brains sleep at a given time. If you ever see a dolphin “logging,” or swimming slowly near the surface, they are probably taking a nap.

What about non-mammals? Reptiles and birds exhibit true sleep, but in a different manner than mammals. Reptiles become unconscious, but they do not have a dream component of their sleep cycle. (Yes, snakes can still sleep even though they don’t have eyelids – they sleep with their eyes open.) Birds are very light sleepers, and they rarely fall into a deep sleep stage at all. This means that they, like reptiles, rarely dream (if ever). Fish and amphibians reduce their awareness of their surroundings, and spend time in an energy-saving state called “rest.” But scientists have found no evidence of the changes in the brain waves of fish and amphibians that would indicate that they are really asleep.

Incidentally, I’ve known a lot of people in my day who claim that they really don’t need very much sleep to function. (Many of these were during my college years.) Sorry folks, but the science has you beat. You may function okay with a greatly reduced sleep schedule. But you’d function a whole lot better if you slept more.