| ||Medical Myths || | Sleep: What's Going on Behind That Shut-
Eye? Last reviewed on January 13, 2011 By Robert H. Shmerling,
M.D. Beth Israel Deaconess Medical Center Have you ever watched
someone sleep and wondered what he or she was dreaming? The
persons outward appearance would never give it away: slow
breathing, eyes occasionally fluttering, but mostly the very
picture of peace and stillness. But, appearances can be
deceiving. When people sleep, theres a lot more going on than
meets the eye. The notion of sleep as the bodys ultimate down
time has some truth to it, but sleep is also an active process,
in which the brain can be remarkably busy, even if the body
remains (mostly) immobile. Whats Going On During Sleep? There is
much about sleep that remains mysterious, but experts divide it
into two main categories, based on observations of sleeping
persons and recordings of the brains electrical activity during
sleep: - Non-REM sleep This is divided into four stages, with
Stage 1 the lightest and Stage 4 the