DEAR DOCTOR K: A friend told me that the reason we sleep is to "flush out" our brain. What is this all about? Is this the reason we sleep?
DEAR READER: Many readers have written asking why we sleep, and we discussed it in yesterday's column. Today we will talk about the recent study that you are asking about, which suggests that one reason we sleep may be to flush out the brain. For those who didn't read yesterday's column, a quick summary. There is evidence that during sleep, our mind and body benefits in several ways. Perhaps most obvious, our muscles get a rest. The fortunate exception is the special muscle that is our heart. We don't want it to quit pumping -- ever!