Why is Sleep Restorative?

Scientists have long wondered why sleep is restorative and why lack of sleep impairs brain function.  Now, new animal research published in the October 18th edition of Science suggests that the sleep state helps clear the body of potentially toxic central nervous system metabolites.  It seems that the sleep-wake cycle regulates an internal “flushing” system which is responsible for clearing waste from the brain and spinal cord.  This research has not yet been duplicated in humans.  But if it is it might lend credence to the old saying “a good night’s sleep can clear the brain”.