What goes on in your brain when you're sleep deprived and how does it affect your ability to process information and make decisions?
A research study conducted at Washington State University into the effects of sleep deprivation on executive functioning—the ability to initiate, monitor and stop actions to achieve objectives—has yielded surprising results and caused a shift in the current thinking on this topic.
Published in the January 2010 issue of the journal "SLEEP," the study found that sleep deprivation affects distinct cognitive processes in different ways. The researchers found that working memory—a key element of executive functioning—was essentially unaffected by as much as 51 hours of total sleep deprivation. Instead, they saw a degradation of non-executive components of cognition, such as information intake, that accounted for the overall impairment in subjects' performance on cognitive tasks. In other words, the sleep deprived brain appears to be capable of processing information, but this information may be distorted before it can be processed.
These results challenge an existing theory that states that sleep deprivation affects executive functions more than non-executive cognitive processes. They also show that previous experimental support for this theory was hampered by task impurity, the problem that any cognitive performance task involves a number of intertwined cognitive processes that must be distinguished to really understand the effects of sleep deprivation on cognitive performance.
"These findings are significant for our understanding of how sleep deprivation affects the brain," said Hans Van Dongen, principal investigator on the study and a research professor in the WSU Sleep and Performance Research Center. "They show that a large body of research on the effects of sleep deprivation needs to be revisited to verify the conclusions, which may have been drawn incorrectly because of task impurity issues."
The study looked at 23 subjects, who spent 6.5 consecutive days in a controlled laboratory environment. One group was kept awake for two consecutive nights (62 hours), while the other was on a normal sleep schedule. Three times throughout the experiment, the subjects completed an executive functions task battery composed of tasks that were selected because they allowed for important executive functions to be examined separately from non-executive components of cognition. The task battery measured such executive functions as working memory scanning efficiency, resistance to proactive interference and verbal fluency.
The paper was authored by Adrienne Tucker, a doctoral student in WSU's experimental psychology program who carried out the study as part of her dissertation research. In addition to Van Dongen, her co-authors were WSU professors of psychology Paul Whitney and John Hinson and research professor Gregory Belenky, director of the Sleep and Performance Research Center. Funding for the research came from the Department of Defense Congressionally Directed Medical Research Programs.
Van Dongen and his colleagues first came up with their new perspective following earlier research studies that examined individual differences in the effects of sleep deprivation, which showed that these differences depended on the task being performed.
"This suggested that sleep deprivation can affect multiple aspects of cognitive task performance in different ways, and that we should look at separate components of cognition and not just overall task performance," Van Dongen said.
Their recent study was the first step in a new line of research the researchers are pursuing, in which they will investigate the effects of sleep deprivation on a variety of distinct cognitive processes. They are planning follow-up studies that will examine how distinct components of decision making are affected by sleep deprivation and how this influences the overall decisions people make. Ultimately, this may lead to the development of interventions that target the components of cognition most affected by sleep deprivation. Such interventions could improve decision making in situations where getting more sleep is not an option. This work will have important implications for emergency responders, police officers, military personnel and anyone required to make sound decisions in safety-critical environments with little opportunity for sleep.
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