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Sleep-deprived Brains Alternate Between Normal Activity And ‘Power Failure’

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Neuroscience researchers at the Duke-NUS Graduate Medical School in Singapore have shown for the first time what happens to the visual perceptions of healthy but sleep-deprived volunteers who fight to stay awake, like people who try to drive through the night.

The scientists found that even after sleep deprivation, people had periods of near-normal brain function in which they could finish tasks quickly. However, this normalcy mixed with periods of slow response and severe drops in visual processing and attention, according to their paper, published in the Journal of Neuroscience on May 21.

“Interestingly, the team found that a sleep-deprived brain can normally process simple visuals, like flashing checkerboards. But the ‘higher visual areas’ — those that are responsible for making sense of what we see — didn’t function well,” said Dr. Michael Chee, lead author and professor at the Neurobehavioral Disorders Program at Duke-NUS. “Herein lies the peril of sleep deprivation.”

The research team, including colleagues at the University of Michigan and University of Pennsylvania, used magnetic resonance imaging to measure blood flow in the brain during speedy normal responses and slow “lapse” responses. The study was funded by grants from the DSO National Laboratories in Singapore, the National Institutes of Health, the National Institute on Drug Abuse, the NASA Commercialization Center, and the Air Force Office of Scientific Research.

Study subjects were asked to identify letters flashing briefly in front of them. They saw either a large H or S, and each was made up of smaller Hs or Ss. Sometimes the large letter matched the smaller letters; sometimes they didn’t. Scientists asked the volunteers to identify either the smaller or the larger letters by pushing one of two buttons.

During slow responses, sleep-deprived volunteers had dramatic decreases in their higher visual cortex activity. At the same time, as expected, their frontal and parietal ‘control regions’ were less able to make their usual corrections.

Scientists also could see brief failures in the control regions during the rare lapses that volunteers had after a normal night’s sleep. However, the failures in visual processing were specific only to lapses that occurred during sleep deprivation.

The scientists theorize that this sputtering along of cognition during sleep deprivation shows the competing effects of trying to stay awake while the brain is shutting things down for sleep. The brain ordinarily becomes less responsive to sensory stimuli during sleep, Chee said.

This study has implications for a whole range of people who have to struggle through night work, from truckers to on-call doctors. “The periods of apparently normal functioning could give a false sense of competency and security when in fact, the brain’s inconsistency could have dire consequences,” Chee said.

“The study task appeared simple, but as we showed in previous work, you can’t effectively memorize or process what you see if your brain isn’t capturing that information,” Chee said. “The next step in our work is to see what we might do to improve things, besides just offering coffee, now that we have a better idea where the weak links in the system are.”

Michael W. L. Chee, Jiat Chow Tan, Hui Zheng, Sarayu Parimal, Daniel H. Weissman, Vitali Zagorodnov, and David F. Dinges
Lapsing during Sleep Deprivation Is Associated with Distributed Changes in Brain Activation
J. Neurosci. 2008 28: 5519-5528; doi:10.1523/JNEUROSCI.0733-08.2008

Lapses of attention manifest as delayed behavioral responses to salient stimuli. Although they can occur even after a normal night’s sleep, they are longer in duration and more frequent after sleep deprivation (SD). To identify changes in task-associated brain activation associated with lapses during SD, we performed functional magnetic resonance imaging during a visual, selective attention task and analyzed the correct responses in a trial-by-trial manner modeling the effects of response time. Separately, we compared the fastest 10% and slowest 10% of correct responses in each state. Both analyses concurred in finding that SD-related lapses differ from lapses of equivalent duration after a normal night’s sleep by (1) reduced ability of frontal and parietal control regions to raise activation in response to lapses, (2) dramatically reduced visual sensory cortex activation, and (3) reduced thalamic activation during lapses that contrasted with elevated thalamic activation during nonlapse periods. Despite these differences, the fastest responses after normal sleep and after SD elicited comparable frontoparietal activation, suggesting that performing a task while sleep deprived involves periods of apparently normal neural activation interleaved with periods of depressed cognitive control, visual perceptual functions, and arousal. These findings reveal for the first time some of the neural consequences of the interaction between efforts to maintain wakefulness and processes that initiate involuntary sleep in sleep-deprived persons.

Written by huehueteotl

May 22, 2008 at 7:48 am

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