It’s been a long day. You’re convinced this lecture was supposed to end hours ago. As your eyelids get heavier, your thoughts start losing focus. You’re drifting in and out of consciousness, and before long, you can’t help it anymore. You’ve fallen asleep.
Sleep is a natural part of human biological rhythms, so it’s quite accurate when people say they can’t live without it. But for many of us, sleep remains something of an enigma. What exactly is this thing that we spend one third of our lives doing?
In an attempt to answer this question, scientists use a number of instruments to measure activity in the brain and body while we sleep. The most important of these is the electroencephalograph (EEG), which measures electrical activity in the brain over time.
Based on these brainwave measurements, sleep is divided into five stages. Before the onset of sleep, a period of drowsiness serves as a prelude to the typical sequence of slumber. Electrical activity in the brain during this brief period is dominated by alpha waves, which are also characteristic of meditative states or what athletes experience when they’re “in the zone.”
Sleep begins at Stage One, which usually only lasts a few minutes, and is characterized by theta waves. Stage One is the transition period between sleep and wakefulness, and the experience is similar to that of relaxation. Stage Two lasts slightly longer, and contains a mix of EEG activity. Both Stages One and Two are ‘light sleep,’ so if someone was awoken during these stages they would probably not recall falling asleep at all. Stages Three and Four consist of slow-wave sleep, which is a period of deep sleep dominated by delta waves. These stages are very similar, and correspond with deep sleep.
The fifth stage of sleep is called the rapid eye movement (REM) stage, and that’s where things start getting interesting. REM sleep is the dream stage, where brain waves resemble the electrical activity of someone who is awake. However, the body is virtually paralyzed during the REM stage, which is why we don’t physically act out our dreams.
Research on sleep disorders investigates all the things that can go wrong in and around the sleep period. Insomnia is a chronic problem that involves difficulty getting to sleep, while narcolepsy is a condition marked by sudden and uncontrollable onsets of sleep during normal waking periods. Another unusual condition is somnambulism, or sleepwalking, in which sleepers are up and wandering around while remaining in slow-wave sleep.
All the research being devoted to sleep patterns, mechanisms, and disorders goes to show that sleep is serious business. U of T has its own Centre for Sleep Medicine and Circadian Biology, while a number of its affiliated hospitals and rehab facilities run sleep labs. When it comes to research, sleep really is a full-time job.
