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DURHAM, N.C. – 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."

Other authors of the study include Jiat Chow Tan, Hui Zheng,
and Sarayu Parimal of the Cognitive Neuroscience Lab at the
Duke-NUS Graduate Medical School; Daniel Weissman of the
University of Michigan Psychology Department; David Dinges of
the University of Pennsylvania School of Medicine; and Vitali
Zagorodnov of the Computer Engineering Department of the
Nanyang Technological University in Singapore.