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What does the brain do while you sleep?
You may think that the brain sleeps when you sleep, but it doesn't. It is just as active as when you are awake.
Even when you're sleeping, your brain controls your heartbeat, breathing, and other body functions. Also, while you are asleep, millions of signals are being sent back and forth inside your brain.
Doctors can measure the number and speed of these signals with a special machine. The machine displays the signals as patterns of wavy lines (sometimes called brain waves.) This display is called an EEG. Doctors use EEGs to help them find out what is wrong with a patient's brain.
The wave patterns change as your brain becomes more or less active. When you are awake and thinking hard about something, the waves are small and spiky. When you are watching television, for example, just relaxed, the waves are much taller and wider.