Question: What would be the differences between sleeping for 7-8 hours in a row and holding two 4 hour sleeping sessions in a day?
Answer: I know of no research that has examined this particular pattern -- two 4-hour sleeping sessions -- so a true comparison isn't possible. But that's the way human beings naturally slept from recorded time until the Industrial Revolution and the invention of the light bulb, according to historian A. Roger Ekirch of Virginia Tech, author of "At Day's Close: Night in Times Past." People slept in two roughly four-hour segments, with an hour or more of awake time in between. And one National Institutes of Medicine study found that when volunteers spent 14 hours in bed in the dark for four weeks, a pattern emerged of two-four hour sleep segments, with no ill effects to their health.
-- Susan Brink, Health section staff writer