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Study reveals how your brain sleeps
By Robert Roy Britt (LiveScience.com)
Updated: 2005-09-30 16:56
Your brain never stops working. But it does cease talking to itself when you
lose consciousness, a new study shows.
Scientists have long wondered what the brain does and doesn't do during deep
sleep. It remains active, they know. So what's the difference between
consciousness and the lack of it?
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.
Tononi's team used a non-invasive procedure to activate select parts of the
brain. Subjects had electrodes attached to their heads to monitor how each
stimulation triggered reactions elsewhere.
In the early morning, when subjects were dreaming, signals careened around
the noggin similarly to when they were awake. But at night, during deeper sleep,
the picture was much different.
"During deep sleep early in the night," Tononi said, "the response is
short-lived and doesn't propagate at all."
Consciousness has long mystified scientists. The new finding suggests that it
depends on the brain's ability to integrate information, Tononi says.
The compartmentalization might also help the brain's synapses, which make all
the connections that give us thought, to take a break, according to Tononi's
colleague, Marcello Massimini.
"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.
The machine used to conduct the experiments is new. It generates a magnetic
field to provide stimulation, and Tononi's team expects this to be the first of
many similar studies that will help researchers better understand the mind and
specific disorders of the brain.
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