What Happens when we sleep?

There isn't an automatic "switch" that flips off when we fall asleep and on when we wake up, says Dr. Leonid Kayumov, director of the sleep clinic at U of T's psychiatry department and the University Health Network's Toronto Western Hospital. "There are several stages we go through in the night." In the first stage, we are lying in bed awake but feeling drowsy. We can still hear cars speeding by the bedroom window or our partner coughing next to us. In the second stage, consolidated sleep, we're lightly dozing but can be wakened easily with a firm shake. However, we've lost touch with the outside world. "People spend 50 per cent of their sleep time in this phase although its function is still not clear," Kayumov says. The third and fourth stages are characterized by deep or restorative sleep. It is during these stages that we receive our most restful sleep. Insomniacs, people suffering from depression, substance abusers or shift workers almost never reach these stages, he says. "They never feel rested." Once we move through the first four phases, we enter the REM stage (Rapid Eye Movement). "We have all heard the expression 'sleeping like a log,'" Kayumov says. "Well, during REM, our bodies are doing quite the opposite. Our heart is palpitating quickly; our eyes are darting back and forth beneath our eyelids; our brain metabolism is working in overdrive." And, during REM, we dream, says Kayumov. While we'll have numerous dreams in this stage, we'll only remember those that occur in the morning hours just before we wake up. Scientists also believe that REM sleep may also play an important role in learning and memory. The first four stages and the initial REM stage take about 90 minutes. Then, the whole cycle begins again, repeating itself four to six times over the course of the night, finishing with REM during the early hours of the morning before waking. The hours just before we wake are also prime times for heart attacks, Kayumov says. "So sleep can be very dangerous but very necessary. If we don't sleep for 10 days, we will die. In contrast, humans can go 60 days without food." As we age, the quality of our sleep deteriorates. Ten year olds, who emit growth hormones while they're asleep, spend more than 25 per cent of their sleep time in deep sleep. By age 40, men spend only 10 per cent and women, 12 to 14 per cent, in a state of deep sleep. After 60, men's deep sleep time bottoms out at zero per cent while women retain about 10 per cent deep sleep. "It is quite possible that life expectancy is also related to these stages," Kayumov says. "Women may live longer because they are able to maintain a small percentage of deep sleep into their late 70s." So how can you get a good night's rest? Kayumov suggests the following "sleep hygiene" tips: * Avoid caffeinated beverages in the afternoon and evening. Caffeine stays in the bloodstream for 12 hours after it is consumed. * Don't eat a heavy meal or drink alcohol right before going to bed. * Have a light snack instead. * Try to exercise three to four hours before you hit the sack. * Take a warm bath, meditate or have your partner give you a light massage to relax you. * Establish a regular routine of waking up and falling asleep. (Dr. Leonid Kayumov is an assistant professor of psychiatry at U of T, a position he has held for the past four-and-a-half years. He has published numerous studies on sleep disorders. His research interests lie in the treatment of insomnia, circadian rhythm disorders and sleep disruption related to psychiatric conditions.)