The Secret Life of the Brain
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Episode 3: The Teenage Brain - Why Do We Sleep?

When measured using EEG, the electric activity of a brain when asleep is no less hectic than it is when awake. There is a difference, though, between two different phases of sleep. Right after falling asleep, the brain demonstrates slow EEG activity. This stage is called slow wave sleep (SWS). However, after a while, the brain goes into the turmoil of the second stage, which due to its similarity to the brain activity of attentive wakefulness, is known as paradoxical sleep. In this stage, the EEG reveals very fast activity. At the same time, the eyes move rapidly, giving this stage its other famous name -- REM (Rapid Eye Movement) sleep. REM sleep is also the time during which we dream.

A number of fascinating experiments suggest that this jittery second stage is the daily session of memory maintenance and that during this time, the brain reviews and sorts the knowledge that it has encountered during the day. Some of it is discarded and some of it is stored in the appropriate context. According to this theory, sleep is required for learning and memory.

In a few experiments, rats were trained to find their way through a maze while electrodes were recording the activity of their brain. When the rats fell asleep, the brain started to behave oddly. In light of difficulties of getting a clear verbal description from the rats regarding their dreams, we can rely only on the pattern of their brain activity. The rats' brain activity during sleep was highly similar to the activity during the training. The brain seemed to reconstruct the experience of the day. In their dreams, the rats were again chasing the cheese through the maze.

Other experiments supplied more direct evidence that sleep is crucial for learning. Human subjects were trained to identify letters that appeared for a blink of an eye on a computer screen. Then, half of the subjects were sent home to sleep, while the other half were deprived of sleep for the entire night, and only then went home to rest. Two days later when all the subjects were already rested and refreshed, the scientists checked their ability to read the flashing letters. None of the participants were tired, and yet the people who went to sleep right after the training performed much better than the ones who went to sleep a day later. This suggests that the night sleep immediately after the activity was crucial for gaining the most from the training session. Without it, the training was much less effective.

The fact that during their formative years of childhood and adolescence, people sleep much more than during their adulthood, also supports the view that sleeping plays a role in learning. Yet, some scientists claim that this evidence is still weak, and more importantly, that other experiments yield contradicting results. Therefore, they argue, declaring that the mystery of sleep is resolved, and that the main function of sleep is to enhance learning, would be premature.

Only future research can decide this debate. In the mean time, if you are planning to pull an all-nighter before a big test, you may want to reconsider. When you go to sleep your brain may still be studying. Perhaps this night session is as crucial for your success as the learning you do when you are awake.

Written by Yanay Ofran.

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