Sleep deprivation takes a heavier toll on the performance and alertness of people who are extroverts than it does on their introverted counterparts, according to results of a randomized clinical study.
Extroverts had lower scores on tests of alertness and wakefulness during 36 consecutive hours awake, including a 12-hour period of social interaction, researcher Tracy L. Rupp of Walter Reed Army Institute of Research in Silver Spring, Md., and co-authors reported in the November issue of Sleep.
In contrast, 36 hours of sleep deprivation that included no social interaction had minimal effect on performance or alertness of extroverts or introverts.
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The findings provide insights into interindividual differences in vulnerability to sleep deprivation, particularly interaction between personality traits and social conditions. However, the effect of the interaction was the opposite of what the investigators had hypothesized.
"Although the hypothesized main effects of social condition and personality were not confirmed, the significant interaction between these two factors tends to confirm our primary hypothesis that social experience does significantly affect the ability to resist subsequent sleep deprivation," they wrote in the discussion of their findings.
"But this effect is mediated by individual differences in introversion-extroversion, a personality trait that is believed to reflect general cerebral arousal level."
The findings reflect the investigators' ongoing investigation of Eysenck's theory, which revolves around the concept of cortical arousal as a determinant of introverted or extroverted personality.
According to the theory, social gregariousness and sensation-seeking behaviors arise, at least in part, from lower levels of tonic arousal. Because of their presumed lower level of cortical arousal, extroverts seek out social contact and stimulation to increase brain arousal to optimum levels, the authors noted.
In contrast, introverts are thought to have relatively higher levels of cortical arousal and avoid socially active environments that would lead to more cortical arousal. Consistent with the theory, Rupp and colleagues previously reported that higher scores on a test of introversion were associated with greater resistance to sleep deprivation.
To continue their investigation of the theory, the authors recruited 48 volunteers for a study of the interaction among personality traits, social exposures, and vulnerability to sleep deprivation. All participants completed a personality inventory assessment that led to categorization of 23 participants as extroverts and 25 as introverts.
The participants were randomly assigned to one of two social experiences, which followed eight hours in bed and two hours to eat breakfast and get ready for the evaluation.
Participants assigned to the socially enriched condition could watch television, play games, read, or eat, and remained with laboratory technicians, who were instructed to keep the participants engaged socially throughout the exposure.
Participants assigned to the socially impoverished condition had access to the same activities as in the socially enriched condition, but had no interaction with each other or with technicians.
Both social conditions lasted 12 hours (10 a.m. to 10 p.m.), and was followed by 22 hours of sleep deprivation, during which time participants were tested hourly for alertness and performance. Technicians monitored participants continuously to ensure that participants did not fall asleep. All told, participants remained awake for 36 consecutive hours.
During sleep deprivation, scores for speed on the Psychomotor Vigilance Test (PVT) deteriorated in all groups but was more pronounced in extroverts assigned to the socially enriched exposure compared with extroverts assigned to the socially impoverished condition at 4 a.m., 6 a.m., and noon.
The socially impoverished condition had minimal impact on test performance or subjective sleepiness in any of the groups.
"The ability of introverts to resist sleep loss, on the other hand, was relatively unaffected by the social environment," the authors noted.