Study Reveals How Your Brain Sleeps - Yahoo! News: "When we're awake, different parts of the brain use chemicals and nerve cells to communicate constantly across the entire network, similar to the perpetual flow of data between all the different computers, routers and servers that make up the Internet.
In the deepest part of sleep, however, the various nodes of your cranial Internet all lose their connections.
'The brain breaks down into little islands that can't talk to one another,' said study leader Giulio Tononi of the University of Wisconsin-Madison."

This process would allow cortical circuits to eliminate noisy synapses and renormalize in order to be ready for the next day," Massimini told LiveScience. The reduced activity might also help explain why performance in various tasks improves after sleep, he said