A new [removed]study[/removed] in rats is shedding light on how sleep-deprived lifestyles might impair functioning without people realizing it. The more rats are sleep-deprived, the more some of their neurons take catnaps—with consequent declines in task performance. Even though the animals are awake and active, brainwave measures reveal that scattered groups of neurons in the thinking part of their brain, or cortex, are briefly falling asleep, scientists funded by the National Institutes of Health have discovered.
"Such tired neurons in an awake brain may be responsible for the attention lapses, poor judgment, mistake-proneness, and irritability that we experience when we haven’t had enough sleep, yet don’t feel particularly sleepy," explained Giulio Tononi, MD, PhD, of the University of Wisconsin-Madison. "Strikingly, in the sleep-deprived brain, subsets of neurons go offline in one cortex area but not in another—or even in one part of an area and not in another."
Previous studies had hinted at such local snoozing with prolonged wakefulness. Yet little was known about how underlying neuronal activity might be changing.
To learn more, the researchers tracked electrical activity at multiple sites in the cortex as they kept rats awake for several hours. They put novel objects into their cages—colorful balls, boxes, tubes, and odorous nesting material from other rats. The sleepier the rats got, more subsets of cortex neurons switched off, seemingly randomly, in various localities. These tired neurons’ electrical profiles resembled those of neurons throughout the cortex during NREM or slow wave sleep. Yet, the rats’ overall EEG, a measure of brain electrical activity at the scalp, confirmed that they were awake, as did their behavior. So neuronal tiredness differs from more overt microsleep that is sometimes experienced with prolonged wakefulness. It is more analogous to local lapses seen in some forms of epilepsy, suggest the researchers.
Tononi and colleagues report their findings online in the April 28, 2011, issue of the journal Nature.