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.