April 4, 2003

UCSD Studies May Identify People Who Perform Well With Little Sleep

Some people thrive on little sleep, while others drag through the day if they don't get eight hours of shut-eye. For most individuals, sleep deprivation isn't a factor in their daily lives. For others long-haul truck drivers, pilots, and soldiers participating in the Iraqi war lack of sleep can cause lapses in performance and possibly jeopardize lives.

Recent news reports from the Iraqi war describe exhausted soldiers who've battled their way through hundreds of miles to reach Baghdad. USA Today, for example, quoted Lt. Col. Jim Chartier, commander of the Marine 1st Tank Battalion, as saying that sleep deprivation has been their biggest enemy, making easy tasks difficult.

While currently there is no evidence pinpointing the biological conditions that make some people function well with little sleep, the Department of Defense is supporting two studies at the University of California, San Diego (UCSD) School of Medicine to find those differences. One study, funded by the U.S. Navy, will use functional magnetic resonance imaging (fMRI) brain scans to study healthy adults who function well with very little sleep on a regular basis, and individuals who normally sleep more than average.

"The idea is to see if there are baseline differences in brain function due to habitual sleep times and to see if one group or the other is less vulnerable to the effects of sleep loss," said Sean P.A. Drummond, Ph.D., UCSD assistant professor of psychiatry. "We have seen some informal evidence of differential responses in people, but there hasn't been a formal study to evaluate these differences."

The second study, funded by the U.S. Army, will use fMRI to explore longer-term sleep deprivation, as much as 62 hours without sleep, and the impact it has on brain function in people who sleep "normal" amounts.

"These studies are based on previous work we have done that suggest the brain may be able to compensate for sleep loss, at least in certain circumstances," Drummond said.

UCSD studies published in 1999, 2000 and 2001 examined the effects of 35 hours of sleep deprivation on cognitive performance, comparing cerebral activation during performance of verbal learning, arithmetic and divided attention tasks. The researchers found that some areas of the brain appeared to compensate for other areas affected by sleep deprivation. For example, regions of the brain's prefrontal cortex (PFC) displayed more activity in direct correlation with the subject's sense of sleepiness; the sleepier the subject, the more active the PFC. Furthermore, the temporal lobe, a brain region involved in language processing, was activated during verbal learning in rested subjects but not in sleep deprived subjects.

Additionally, a region of the brain called the parietal lobes, not activated in rested subjects during the verbal exercise, was more active when the subjects were deprived of sleep. The parietal region normally performs somewhat different functions in the learning process than the temporal region. Although subjects' memory performance was less efficient with sleep deprivation, greater activity in the parietal region was associated with better memory.

During their studies, the researchers noted great variability in participant responses to sleep deprivation, leading them to hypothesize that biological differences between people might predispose some people to function better than others when sleep deprived.

If the new studies can identify the biological make-up of these higher-performing, sleep-deprived individuals, then they may become candidates for a variety of jobs that require long periods of wakefulness.

For information on enrolling in the sleep studies, call UCSD at 858-642-1259.

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Studies in Journals (call 619-543-6163 to request copies of studies):

"The Effects of Total Sleep Deprivation on Cerebral Responses to Cognitive Performance," Neuropsychopharmacology 2001 (one of the Nature magazines), Vo. 25, S5

"Increased cerebral response during a divided attention task following sleep deprivation," Journal of Sleep Research (2001), 10, 85-92

"Altered brain response to verbal learning following sleep deprivation," Nature, Vo. 403, 10 February 2000

"Sleep deprivation-induced reduction in cortical functional response to serial subtraction," NeuroReport 10, 3745-3748 (1999)

News Media Contact:
Sue Pondrom
619-543-6163
spondrom@ucsd.edu

UCSD Health Sciences Communications HealthBeat: http://health.ucsd.edu/news/