It's one of the great ironies of science really, the fact that the phenomenon of sleep — which is essential to our health and survival and which totally occupies one-third of our lives — has, until relatively recent times, received no respect at all from the world of serious science. Previous generations of scientific thinkers regarded sleep as nothing more than a monolithic loss of consciousness; an important function, but not one worthy of serious scientific study. As a result, some brilliant minds have cooked up some very kooky notions about the notion of slumber. Many 19th-century physicians, for example, thought sleep was due to a lack of blood flow to the brain; others thought it was too much blood that doped us up and turned out the lights. The great philosopher Plato had a different hunch: He thought sleep was caused by vapors rising from the stomach to clog the pores of the brain like an old furnace filter, which would, if you think about it, tend to make a guy drowsy.