New imaging research shows that brain activity differs in sleep-deprived and well-rested people. The study, in the May 21 issue of The Journal of Neuroscience, shows that individuals who are sleep-deprived experience periods of near-normal brain function, but these periods are interspersed with severe drops in attention and visual processing.
This study shows what happens in the sleep-deprived brain and may explain why sleep-deprived people fail to stay alert. “The main finding is that the brain of the sleep-deprived individual is working normally sometimes, but intermittently suffers from something akin to power failure,” said Clifford Saper, MD, PhD, of Harvard University, an expert unaffiliated with the study.
The research team, led by Michael Chee, MBBS, at the Duke–National University of Singapore Graduate Medical School in Singapore (Duke-NUS), used functional magnetic resonance imaging (fMRI) to measure brain blood flow in people who were either kept awake all night or allowed a good night’s sleep. Researchers tested the same participants in both conditions.
During imaging, participants did a task that required visual attention. Researchers showed them large letters composed of many smaller letters. Participants were asked to identify either the large or small letters and to indicate their responses by pushing a button.
Well-rested and sleep-deprived volunteers showed a range of reaction times. Those participants with the fastest responses, both in sleep-deprived and well-rested conditions, showed similar patterns of brain activity. However, well-rested and sleep-deprived participants with the slowest responses—also called attentional lapses—showed different patterns of brain activity.
Previous research showed that attentional lapses normally induce activity in frontal and parietal regions of the brain, “command centers” that may compensate for lost focus by increasing attention. However, during attentional lapses, Chee and colleagues found reduced activity in these brain command centers in sleep-deprived compared to well-rested volunteers. This finding suggests that sleep deprivation reduces the brain’s ability to compensate for lost focus.
Sleep-deprived people also showed reduced activity in brain regions involved in visual processing during attentional lapses. Because the brain becomes less responsive to sensory stimuli during sleep, reduced activity in these regions suggests that, during attentional lapses, the sleep-deprived brain enters a sleep-like state.
“To my knowledge, this is one of the first studies to look carefully at brain imaging during lapses of consciousness after sleep deprivation, the equivalent of ‘blanking out,’” said Emmanuel Mignot, MD, PhD, at Stanford University, who was not involved in the study. Although attentional lapses result in the same behaviors, “lapses due to sleep deprivation are clearly different neurobiologically than lapses in well-rested people,” Mignot said.
Saper says the study highlights the importance of preventing sleep deprivation in people who are doing critical tasks, like night driving. Although sleep deprivation harms decision making and may increase on-the-job errors, sleep-deprived workers may not know they are impaired. “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,” study author Chee said.
This research was performed collaboratively by researchers at the Duke-NUS Graduate Medical School, University of Michigan, and University of Pennsylvania. 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 National Space Biomedical Research Institute, and the Air Force Office of Scientific Research.
The Journal of Neuroscience is published by the Society for Neuroscience, an organization of more than 38,000 basic scientists and clinicians who study the brain and nervous system. Chee can be reached at mchee@pacific.net.sg.