The ability of the brain to function following sleep deprivation appears to vary with the task at hand, and in some cases the brain attempts to compensate for the adverse effects caused by lack of sleep, according to a study published in the Feb. 10 issue of Nature.
A team of researchers from the UCSD School of Medicine and the Veterans Affairs Healthcare System, San Diego used functional magnetic resonance imaging (fMRI) technology to monitor activity in the brains of sleep-deprived subjects performing simple verbal learning tasks.
They were somewhat surprised to learn that 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.
“Only in recent years have we begun to realize the prevalence and severity of sleep deprivation in our population, with a significant number of people doing shift work, suffering from jet lag and so forth,” said J. Christian Gillin, M.D., professor of psychiatry at the UCSD and the San Diego VAMC, and an author of the Nature paper. “Yet, we don’t know very much about how sleep deprivation impairs performance, and how precisely the brain reacts to lack of sleep. These findings are just a beginning, and as we learn more, perhaps will be able to devise interventions to alleviate the behavioral impairments associated with lack of sleep.”
For this study, thirteen normal healthy subjects were first evaluated in a sleep laboratory to determine that their sleep patterns were normal. They were then kept awake and carefully monitored in a hospital sleep laboratory for over a period of about 35 hours. During this experiment, they were given separate cognitive tasks which they performed while undergoing fMRI scans which produced images revealing brain activity. These images reveal increased and decreased activation of specific regions of the brain in each subject from a rested state through various stages of sleep deprivation.
This study and another study published by Gillin’s team in the December 1999 NeuroReport indicate that the brain is extremely dynamic in its efforts to function when deprived of sleep, though the consequence for the subject is diminished ability to perform basic cognitive tasks. It is also apparent that the effects of sleep loss are different depending on the cognitive task the brain is asked to perform.
In the earlier study, the team studied sleep-deprived subjects performing an arithmetic task involving subtraction. In that study, they observed that the brain regions activated in rested subjects doing the arithmetic problems were not active in the sleep-deprived subjects. No other region of the brain became activated when subjects performed arithmetic when sleep-deprived. Subjects had fewer correct answers and omitted more responses when sleepy than when rested.
Why the sleepy brain displays increased activity in certain regions when confronted with verbal problems, but in general shows less activity when challenged with arithmetic problems, is not entirely clear.
“It is possible that when the prefrontal and temporal regions were affected by sleepiness, the brain shifted the verbal processing to another system in the parietal lobes that could compensate for the loss of function. This suggests that parietal lobes might play a special role in the brain’s compensation for sleepiness,” said Gregory G. Brown, Ph.D., associate professor of psychiatry at UCSD and a member of the team.
“However, the parietal lobes are the system primarily associated with arithmetic performance when subjects are well rested, so when it becomes less responsive with sleeplessness, there is not a brain system available to come online to compensate for the negative effects of sleep deprivation,” he said.
“It is important to remember that sleep deprivation does have detrimental effects, which we sometimes forget as we push workers, students and others to perform even when they are functioning with a lack of sleep,” said Gillin.
The researchers speculate that the brain is adversely affected by sleep deprivation because certain patterns of electrical and chemical activity that occur during sleep are interrupted, impeding the brain’s ability to function normally.
Source: UCSD School of Medicine and the Veterans Affairs Healthcare System, San Diego Press Release, February 9, 2000.