More threads by David Baxter PhD

David Baxter PhD

Late Founder
Is Your Brain Sleeping While You're Awake?
by Christine Dell'Amore, National Geographic
April 27, 2011

Key parts of sleep-deprived brains may go offline, hindering decision-making.

If you think you can function on minimal sleep, here's a wake-up call: Parts of your brain may doze off even if you're totally awake, according to a new study in rats.

Scientists observed the electrical activity of brains in rats forced to stay up longer than usual. Problem-solving brain regions fell into a kind of "local sleep"?a condition likely in sleep-deprived humans too, the study authors say.

Surprisingly, when sections of the rats' brains entered these sleeplike states, "you couldn't tell that [the rats] are in any way in a different state of wakefulness," said study co-author Giulio Tononi, a neuroscientist at the University of Wisconsin, Madison.

Despite these periods of local sleep, overall brain activity?and the rats? behaviors?suggested the animals were fully awake.

This phenomenon of local sleep is "not just an interesting observation of unknown significance," Tononi said. It "actually affects behavior?you make a mistake." For example, when the scientists had the rats perform a challenging task?using their paws to reach sugar pellets?the sleep-deprived animals had trouble completing it.

Sleep Allows Neurons to Reset?
Tononi and colleagues recorded the electrical activity of lab rats via electroencephalogram (EEG) sensors connected to the rodents' heads. As predicted, when the rats were awake, their neurons?nerve cells that collect and transmit signals in the brain?fired frequently and irregularly. When the animals slept, their neurons fired less often, usually in a regular up-and-down pattern that manifests on the EEG as a "slow wave." Called non-rapid eye movement, this sleep stage accounts for about 80 percent of all sleep in both rats and people.

The researchers used toys to distract the rats into staying awake for a few hours?normally "rats take lots of siestas," Tononi noted.

The team discovered that neurons in two sections of these overtired rats' cerebral cortexes entered a slow-wave stage that is essentially sleep.

Why Do We Sleep?
It's unknown why parts of an awake brain nod off, though it may have something to do with why mammals sleep?still an open question, said Tononi, whose study appears tomorrow in the journal Nature.

According to one leading theory, since neurons are constantly "recording" new information, at some point the neurons need to "turn off" in order to reset themselves and prepare to learn again.

"If this hypothesis is correct, that means that at some point [if you're putting off sleep] you're beginning to overwhelm your neurons?you are reaching the limit of how much input they can get."

So the neurons "take the rest, even if they shouldn't"?and there's a price to pay in terms of making "stupid" errors, he said.

Even "Alert" People Make Mistakes
Sleep deprivation may have dangerous consequences, Tononi said?and those mistakes may become more common.

For one, many people are getting fewer z's. In 2008 about 29 percent of U.S. adults reported sleeping fewer than seven hours per night, and 50 to 70 million had chronic sleep and wakefulness disorders, according to the U.S. Centers for Disease Control and Prevention. Adults generally need about seven to nine hours of sleep a day, according to the National Sleep Foundation.

What's more, you don't need to feel sleepy to screw up, Tononi emphasized. "Even if you may feel that you're fit and fine and are holding up well," he said, "some parts of your brain may not [be] ... and those are the ones that make judgments and decisions."


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David Baxter PhD

Late Founder
Tired Neurons Caught Nodding Off in Sleep-deprived Rats

Tired Neurons Caught Nodding Off in Sleep-deprived Rats
NIMH
April 27, 2011

Performance Decline Belies Seeming Wakefulness ? NIH-funded Study

A new study 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, M.D., Ph.D., 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."

Tononi and colleagues report their findings online in the April 28, 2011 issue of the journal Nature. Their study was funded in part by the NIH's National Institute of Mental health and a NIH Director's Pioneer Award, supported through the Common Fund, and administered by NIMH and the National Institute on Neurological Disorders and Stroke.

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" ? 3-15-second lapses with eyes closing and sleep-like EEG - that is sometimes experienced with prolonged wakefulness. It is more analogous to local lapses seen in some forms of epilepsy, suggest the researchers.

However subtle, having tired neurons did interfere with task performance. If neurons switched off in the motor cortex within a split second before a rat tried to reach for a sugar pellet, it decreased its likelihood of success by 37.5 percent. And the overall number of such misses increased significantly with prolonged wakefulness. This suggests that tired neurons, and accompanying increases in slow wave activity, might help to account for the impaired performance of sleep-deprived people who may seem behaviorally and subjectively awake.

Subsets of neurons going offline with longer wakefulness is, in many ways, the mirror image of progressive changes that occur during recovery sleep following a period of sleep deprivation. Tononi suggests that both serve to maintain equilibrium ? part of the compensatory mechanisms that regulate sleep need. Just as sleep deprivation produces a brain-wide state of instability, it may also trigger local instability in the cortex, possibly by depleting levels of brain chemical messengers. So, tired neurons might nod off as part of an energy-saving or restorative process for overloaded neuronal connections.

"Research suggests that sleep deprivation during adolescence may have adverse emotional and cognitive consequences that could affect brain development," noted NIMH Director Thomas R. Insel, M.D. "The broader line of studies to which this belongs, are, in part, considering changes in sleep patterns of the developing brain as a potential index to the health of neural connections that can begin to go awry during the critical transition from childhood to the teen years."

Reference
Vyazovskiy VV, Olcese U, Hanlon EC, Nir Y, Cirelli C, Tononi G. Local sleep in awake rats. Nature. 2011 April 28.
 
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