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REM Sleep

If you think sleep is when the body simply shuts down, you're much mistaken. Decades of tests involving wires, electrodes and imaginary sheep, have shown us just how complicated a process it is. You don't need a degree in human biology to understand it, but it helps.

While you're asleep your body produces a series of distinct brainwaves. They repeat themselves to form sleep cycles, each lasting around 60 minutes in babies and 90 minutes in adults. During a night, a normal sleeper can expect to go through 4-5 cycles. And each sleep cycle goes through five stages of sleep.

The body is thought to repair and regenerate itself in the fi rst four stages of sleep - commonly known as non-REM sleep (NREM). Stage 5, REM (rapid eye-movement) sleep, is where the fun starts: learning is processed as the brain sorts out and makes sense of the events of the day - the argument you had with your boss, why you lost at squash and why you bought that glow-in-thedark razor for your father. You are also most likely to dream.

To make it clearer, I'll take you through a night when you're having no trouble with your sleep. Before falling asleep, you close your eyes, your body relaxes and your brainwaves change from the rapid beta waves to slower, sleepier alpha waves. It's similar to the feeling you get when you keep nodding off while trying to read War and Peace. Then you get to:

Stage 1: light sleep. Heart rate and body temperature drop and brainwaves slow down even more. It lasts a few minutes and you can easily be woken up during this stage. Ever been woken up by your own snoring on the bus and had to get off three stops early to escape public humiliation? Yes? Well you were probably in light sleep.
Stage 2: proper sleep. This phase usually lasts about 30-40 minutes and although it doesn't take much to wake you up, you're likely to feel groggy.
Stages 3 and 4: deep sleep. In stage 3, brainwaves give way to the slowest brainwaves - the delta waves. By stage 4, not much is going to wake you - a stampede of elephants could come charging through your room and you won't even stir, although amazingly hearing a familiar name could possibly rouse you. Your oxygen levels, heart rate and breathing levels are at their lowest. Now the growth hormone is released, which helps cell renewal, building new tissue and repairing damaged cells.
Stage 5: REM sleep. This is when you have your most vivid dreams. Although you're not aware of it, your body and brain come to life - your brain is as active as it is when you're awake. Your eyes dart about, while your heart rate, breathing rate and blood pressure all rise and can be erratic - this explains those moments when you wake up from a disturbing dream with your heart thumping. Brainwaves speed up and slow down dramatically. Your memory is also being recharged. Most of us have gone to bed trying without success to remember something, only to find that when we awake the next morning the answer pops into our head as if by magic. Apart from finger and facial twitching, most of your muscles become paralysed to stop you acting out your dreams.

These stages alternate throughout the night and most people normally wake up for a few seconds, five times an hour - although they won't remember it. The exact pattern varies from person to person and with age. Babies spend about half their sleeping time in REM sleep, adults about a quarter. If you miss out on sleep, it's the lighter stages of sleep - 1 and 2 - that tend to be lost. The body will always do its best to catch up on deep sleep first, then REM sleep.


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