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SINGAPORE -- When an air traffic controller at the end of a
double shift forgets the location of an aircraft that had
recently appeared on his screen, it may be that he did not
properly take in the visual information.

While it is well documented that sleep deprivation leads to
short-term memory loss, it had been believed that it was the
result of the brain not being able to assemble and "file away"
the information it received in its proper place.

However, experiments by researchers from the Duke University-National University of
Singapore Graduate Medical School at the SingHealth
Cognitive Neuroscience Laboratory suggest that the problem
occurs earlier in the information-gathering process.

"We generally think of memory decline as a result of faulty
storage of information," said cognitive neuroscientist Michael
Chee, M.D., whose findings are published online in the journal
Proceedings of the National Academy of Sciences. The research
was supported by Singapore's DSO National Laboratories, the
SingHealth Foundation and the Shaw Foundation.

"However, if the information is not properly handled by the
visual system, either as a result of a failure to direct
attention appropriately or a failure of visual areas to process
what is seen, you can forget about the later stages of
information consolidation and storage," Chee said. "When people
are sleep deprived, they may not be seeing what they think they
should be seeing, and it appears that this is what contributes
to memory declines following sleep deprivation."

In their experiments, the researchers found that people who
are sleep deprived can see and take in only a small number of
objects at a time. Objects over this threshold are lost.

"Our findings support and help explain what experts have
known about designing critical information-delivery systems
such as flight displays on aircraft or medical monitors in
intensive care units: you have to carefully select what is
displayed on the screen at any one time," Chee said. "The brain
is not in a good state to process visual information, let alone
too much of it, when it is sleep deprived."

The researchers tested 30 healthy volunteers on the same
memory tests after a regular night's sleep and also after 24
hours without sleep. The researchers used a technique called
functional magnetic resonance imaging to measure which areas of
the volunteers' brains were active during the tests. This
technique measures the changes in blood flow and blood
oxygenation in the brain in response to different stimuli.

The researchers briefly flashed increasing numbers of
colored squares on a computer screen and asked the volunteers
to remember if a new square displayed on the screen was the
same color as any of the earlier squares. The idea was that
increasing memory load would tax the storage system and give
insight into memory capacity.

"We found that visual short-term memory capacity dropped
following sleep deprivation and that this was likely due to a
reduced ability to focus attention," Chee said.

The sleep-deprived volunteers showed brain activation
deficiencies with visual arrays involving as few as one or two
squares, indicating that the deficit in visual processing was
quite severe, he said.

"A small group of sleep-deprived volunteers who had better
performance were better able to tune out distractions, but even
they suffered from compromised visual attention and
processing," Chee said.

Chee's laboratory is continuing to investigate the changes
that occur within the visual and attention systems during sleep
deprivation. He hopes the use of functional magnetic resonance
imaging could help identify people who might be more
susceptible to the attention deficits that occur during sleep
deprivation.

"It might be possible to determine whether or nor certain
people would be suitable candidates for occupations where
repeated and prolonged sleep deprivation is a routine part of
the job," Chee said.

Lisa Chuah of the Cognitive Neuroscience Laboratory was a
co-investigator in the research project.

About the Duke-NUS Graduate Medical School Singapore

The Duke-NUS Graduate Medical School Singapore is a
collaboration between the Duke University School of Medicine
and the National University of Singapore (NUS). The Duke-NUS
Graduate Medical School Singapore offers a graduate-entry
medical program based on the Duke model of education, with one
year dedicated to independent study and research projects of a
basic science or clinical nature. Graduates of the program
receive a joint M.D. degree from both Duke University and the
NUS.