What happens when we sleep? This questions has plagued scientists and confused the lay person alike. We know that we need sleep. We know that during sleep our body's cells repair themselves, growth hormones are released, our minds processes information, and we re-energize. We know without sleep our cognitive thinking is poor. We can hallucinate. Our minds fail. We are susceptible to disease and are cranky. What we don't know is why...

Here is an overview of what we know occurs during sleep and four theories that researchers have devised trying to explain why we do need sleep.

FIVE CYCLES

Stage 1 Stage 1 is the time it takes for an individual to actually fall asleep. An average adult spends only 5 percent of their sleeping time in this stage. Our brain waves are high amplitude slow waves and we have occasional alpha waves, which are normally found while we are awake. This is the lightest cycle of sleep and we are often awoken by slight noises or movement.

Stage 2 During this step, our heartbeat and breathing slow. Sleep is deeper than in stage 1. Slow wave sleep occurs with peaks in brain waves, which are referred to as sleep spindles. Our bodies begin to relax in this stage. A normal adult spends 44-55 percent of their time in this stage.

Stage 3 and 4 These two stages are when we are deepest in sleep. Here, our brainwaves are the slowest. Our heartbeat slows and muscles relax completely. This is normally the stage where people sleepwalk. At this stage our bodies operate with a mind of their own and our minds release control. An average adult will spend 15-23 percent of their time in these two stages.

Stage 5 (REM) REM sleep stages lengthen throughout the course of the night. Although your first REM cycle may be only 10 minutes long, your last REM cycle could last up to an hour. At this stage, breathing becomes shallow, heartbeat increases, muscles relax and your eyes may move. Dreams are most vivid and prominent in this stage. Your brain waves closely resemble your brain waves when you are awake. This is the stage that memories and thoughts throughout the day are regarded. Our minds sift through them and decide which memories are keepers that we file away, and which are forgotten. An average adult will spend about 20-25 percent of their sleep time in this stage.

Different studies have shown what the effects of not getting a good night's sleep are. According the American Cancer Society, people who do not

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