Word: slow
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Dates: during 2000-2009
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...slight bias to the cursor's motion, forcing them to adjust their movements. Half the group slept between sessions and the other half did not. Among the sleepers, the part of the brain that was learning to compensate for the bias while awake turned out to have the largest slow waves during sleep. "The bigger the slow waves were in that part of the brain, the better they performed the next day," Tononi says...
...good. But what does it mean? Tononi speculates that instead of strengthening neural connections responsible for a given task, as appears to happen during the day or in REM sleep, slow-wave sleep actually indiscriminately weakens the connections among all nerves. The idea sounds counterintuitive, but it may simply be a matter of self-preservation. "Normally the brain takes up 20% of the energy of the entire body," Tononi explains. Most of that energy goes into sustaining the connecting points, or synapses, between neurons. The more you learn, the greater the number of synapses...
...take a neuroscientist to figure out where that leads. After a few days, the number of new synapses in the brain would require more energy than the body could possibly supply. So some of those connections must be weakened--and the best guess is that it happens during slow-wave sleep...
That explanation is still hypothetical, but Tononi thinks he has evidence to back it up. "In slow-wave activity, all the neurons fire for half a second," he explains. "Then they're totally silent for half a second." For complex bioelectrical reasons, that turns out to be a perfect way for the brain to lower the strength of the connections between its neurons. Intermittent firing makes the connections leaner and more efficient and may even allow the weakest ones to drop out, clearing the mind so that it can learn something new in the morning...
...they right--or does the altered state brought on by caffeine, fatigue and lack of slow-wave sleep merely make them believe they are right? It's a question they might do well to ponder--if only they had the time. --Reported by Anna Macias Aguayo/ Dallas, Paige Bowers/Atlanta, Simon Crittle/ New York and Leslie Whitaker/Chicago