http://news.essilorusa.com/stories/detail/strange-things-your-body-does-...

We’ve all heard that it’s important to make a good night's rest a priority for an overall healthy lifestyle – sleep benefits the body as a whole including your heart, weight, and mind. But did you know there are five stages of sleep? A sleep cycle lasts about 90 minutes moving from light sleep in stage one to deep sleep in stage four. During these first four stages, also called non-rapid eye movement (NREM) sleep, there is very little activity and our eyes generally do not move. The fifth stage of sleep is known as rapid-eye movement or REM sleep, and this is where things get interesting.

Just as the name suggests, REM sleep includes bursts of rapid eye movement that isn’t quite a constant motion but more of darting movements taking our eyes up and down and back and forth. Most of our dreaming occurs during REM sleep, so it’s believed that these eye movements might be related to the visual images we see during dreams. Studies have even shown brainwave patterns in REM sleep to be similar to that recorded during times the body is awake.

While brain activity is heightened during REM sleep, our major voluntary muscle groups – such as leg and arm muscles – are actually paralyzed. This immobility is a good thing, because it prevents our bodies from acting out what's going on in the brain during our dreams.

So what else is happening in REM sleep? Believe it or not, the brain regions associated with learning are stimulated during this stage of the sleep cycle. This could explain study results showing the effect of REM sleep on certain mental skills. One study showed that people taught a skill and then deprived of non-REM sleep could remember what they had learned after sleeping, but those who were taught that same skill and deprived of REM sleep had no recall.

The connection between REM sleep and learning would also explain why infants speed more time in REM sleep than adults. Infants can spend up to 50 percent of their sleep in the REM stage, while adults spend only about 20 percent in REM sleep.

Interestingly, while our brains are inherently connected to our current stage of sleep, our eyes don’t actually send image information to the brain while we’re asleep. In fact, it takes about 30 seconds for your brain to realize you're awake – the connection between your eyes and your brain has to reboot when you wake up.