Desiree B. Killgore

The trait of Introversion-Extraversion predicts vulnerability to sleep deprivation.

According to Eysenck’s theory of Introversion–Extroversion (I–E), introverts demonstrate higher levels of basal activity within the reticular‐thalamic‐cortical loop, yielding higher tonic cortical arousal than Extraverts, who are described conversely as chronically under‐aroused and easily bored. We hypothesized that higher scores on the trait of Extraversion would be associated with greater declines in psychomotor vigilance performance during prolonged wakefulness. We evaluated the relationship between I–E and overnight psychomotor vigilance performance during 77 h of continuous sleep deprivation in a sample of 23 healthy adult military personnel (19 men; four women), ranging in age from 20 to 35 years. At baseline, volunteers completed the Revised NEO Personality Inventory (NEO PI‐R) and completed psychomotor vigilance testing at approximately 10‐min intervals from 00:15 to 08:50 hours over three nights of continuous sleep deprivation. In addition, 12 participants received four repeated administrations of caffeine (200 mg) every 2 h each night. Analysis of covariance and stepwise multiple regression analyses showed that, above and beyond the effects of caffeine, higher Extraversion was significantly related to more extensive declines in speed of responding and more frequent attentional lapses, but only for the first overnight testing session. Sub‐factors of Extraversion, including Gregariousness and higher Activity level were most predictive of these changes following sleep loss. These findings are consistent with Eysenck’s cortico‐reticular activation theory of I–E and suggest that individual differences in the trait of Extraversion confer some vulnerability/resistance to the adverse effects of sleep loss on attention and vigilance.

Executive Functions and the Ability to Sustain Vigilance During Sleep Loss

INTRODUCTION There is considerable individual variability in the ability to sustain performance during sleep loss. Preliminary evidence suggests that individuals with higher trait-like activation/functioning of the prefrontal cortex may be less vulnerable to fatigue. METHODS We tested this hypothesis in a sample of 54 healthy volunteers who were assessed bi-hourly on a variant of the Psychomotor Vigilance Test during 41 h of sleep deprivation. A subset of these subjects, representing the top and bottom 25% of the sample based on their ability to sustain vigilance performance during sleep deprivation, were compared with respect to baseline neurocognitive abilities. RESULTS The sleep deprivation Resistant group (N = 13) scored significantly higher than the sleep deprivation Vulnerable (N = 13) group on all three baseline tasks assessing prefrontal executive function abilities (letter fluency, Stroop Color-Word test, Color Trails Form 2), whereas no differences were found on non-executive function tasks. Similarly, groups showed no differences on demographic variables including age, education, hand preference, morningness-eveningness preference, global intellectual ability, or pre-study sleep history. DISCUSSION Findings are consistent with the hypothesis that greater prefrontal/executive functioning may be protective against the adverse effects of sleep deprivation and suggest that baseline executive function testing may prove useful for prediction of resilience during sleep loss.

Restoration of risk-propensity during sleep deprivation: caffeine, dextroamphetamine, and modafinil.

INTRODUCTION Sleep deprivation alters risk-related judgments, decision-making, and behavioral control. Stimulant medications are used to restore cognitive performance, but their effects on risk-taking and judgment in sleep-deprived subjects have not been explored. METHODS There were 54 healthy adults (29 men, 25 women; age range 18 to 36) who completed a test of cognitive ability and daily measures of risk-taking propensity, including the Brief Sensation Seeking Scale (BSSS), Evaluation of Risks (EVAR) scale, and the Balloon Analog RiskTask (BART). Following 44 h of continuous wakefulness, participants ingested caffeine 600 mg (N = 12), dextroamphetamine 20 mg (N = 16), modafinil 400 mg (N = 12), or a placebo (N = 14) in a double blind manner, and completed risk-taking measures 2 h later (i.e., 0535). RESULTS Relative to rested baseline, the placebo group showed a decline in risk-taking as measured by the BSSS (16% decline), EVAR Danger Seeking (32% decline) and Energy (22% decline), and BART (32% decline), consistent with previous reports of the effects of sleep deprivation. Comparisons among drug conditions showed that dextroamphetamine restored risk-taking propensity and risky behavior to baseline levels, an effect that was significantly greater than placebo or caffeine for several indices of risk-taking, but which did not differ from modafinil. Cognitive ability was significantly correlated with changes on some risk-taking indices following stimulant administration. CONCLUSIONS Stimulant medications, particularly dextroamphetamine, sustained risk-related attitudes and behavior during continuous wakefulness. The extent to which stimulants restore other aspects of judgment during sleep loss remains to be determined.

Morningness-Eveningness Correlates with Verbal Ability in Women but Not Men

Individuals differ along a continuum of preference for diurnal activity level, known as Morningness-Eveningness. Some evidence suggests that an Eveningness orientation (i.e., preference for later rise and bed times) is weakly associated with higher cognitive ability, but no studies have examined this relationship using clinically accepted, psychometrically valid measures of cognitive ability. The present study examined the correlation between Morningness-Eveningness with scores on the Wechsler Abbreviated Scale of Intelligence (WASI) of 54 healthy volunteers. Lower Morningness (i.e., Greater Eveningness) orientation was correlated (r = −.23) with higher Verbal IQ for the entire sample. When the data were examined separately by sex, the correlation between Morningness-Eveningness and Verbal IQ was significant for women (r = −.44) but not for men (r = −.09).

Sex differences in cognitive estimation during sleep deprivation: Effects of stimulant countermeasures

Stimulant medications restore simple alertness during sleep loss, but it is not clear how they affect complex executive functions, particularly in light of sex differences in cerebral organization. The effectiveness of caffeine, modafinil, dextroamphetamine, or placebo for sustaining performance on the Biber Cognitive Estimation Test (BCET) was compared in 29 men and 25 women following 46 hr of sleep deprivation. Stimulants had differential effects on BCET performance as a function of the sex of the subjects. Women receiving placebo or caffeine scored significantly worse than males, while modafinil and dextroamphetamine were effective at sustaining BCET performance of men andwomen.

Baseline Odor Identification Ability Predicts Degradation of Psychomotor Vigilance During 77 Hours of Sleep Deprivation

Scores on the University of Pennsylvania Smell Identification Test, a measure of the functional integrity of the orbitofrontal cortex, were used to predict the vulnerability to cognitive declines during 77 hr of sleep deprivation. Twenty-one healthy volunteers completed the Smell Identification Test at rested baseline followed by repeated psychomotor vigilance testing throughout each night. Participants with better smell identification abilities sustained faster speeds and fewer lapses on the second and third nights of sleep deprivation than participants with lower scores. Individual differences in trait-like functioning of the orbitofrontal cortex are predictive of the ability to sustain alertness and vigilance during continuous wakefulness.

Sex Differences in Self-Reported Risk-Taking Propensity on the Evaluation of Risks Scale

The Evaluation of Risks scale was recently developed as a self-report inventory for assessing risk-taking propensity, but further validation is necessary because most studies have predominantly included male subjects. Because males commonly exhibit greater risk-taking propensity than females, evidence of such a sex difference on the scale would further support its construct validity. 29 men and 25 women equated for age (range: 18 to 36 years) completed the scale. Internal consistency of the scale was generally modest, particularly among women. Men scored significantly higher than women on four of nine indices of risk-taking propensity, including Danger Seeking, Energy, Invincibility, and Total Risk-Propensity. Factors measuring thrill seeking and danger seeking correlated positively with a concurrent measure of sensation seeking. Although the higher scores exhibited by men are consistent with prior research on other measures of risk-taking, further research on this scale with samples including women is warranted.

Odor Identification Ability Predicts Executive Function Deficits Following Sleep Deprivation

ABSTRACT Odor identification ability is sensitive to prefrontal lobe dysfunction and preliminary evidence suggests that this capacity may decline with prolonged wakefulness. We hypothesized that declines in odor identification during a single night of sleep loss might, therefore, be predictive of prefrontal lobe executive function deficits following an additional night of sleep deprivation. Change scores between two administrations of the University of Pennsylvania Smell Identification Test (SIT) during 24 hr of sleep deprivation were used to predict performance on the Wisconsin Card Sorting Test (WCST) following 45 hr of wakefulness in 54 healthy adults. Declines in SIT performance predicted poorer performance on the WCST following an additional night of sleep loss. These findings suggest that individual differences in vulnerability to the effects of sleep loss on odor identification ability are predictive of deficits in executive functioning following additional wakefulness. Odor identification ability may provide an unobtrusive method for assessing vulnerability to sleep deprivation.

Trait-Anger Enhances Effects of Caffeine on Psychomotor Vigilance Performance

This study examined the combined effects of caffeine and the personality attribute of trait-anger on the speed of psychomotor vigilance performance during sleep deprivation. 23 young adult soldiers (19 male) were administered the State-Trait Anger Expression Inventory–2 when well-rested. Participants were then sleep deprived for three consecutive nights (77 hours total) during which they completed repeated psychomotor vigilance testing. Half of the participants received four doses of oral caffeine (200 mg every 2 hr.; 800 mg total) each night, while the other half were administered a placebo. For the first night, higher scores on trait-anger, outward anger expression, and intensity of anger expression predicted better sustained overnight vigilance performance, but only for those volunteers receiving caffeine. These correlations were not significant for the subsequent nights. Findings suggest a possible synergistic effect between personality traits associated with arousal of the central nervous system and vigilance-promoting effects of caffeine.

Effects of Acute Caffeine Withdrawal on Short Category Test Performance in Sleep-Deprived Individuals

Caffeine is a popular stimulant often used to counter the effects of sleep loss and fatigue. Withdrawal from caffeine may produce mild declines in simple cognitive capacities such as attention and concentration, but it is unclear whether more complex cognitive functions, such as abstract reasoning or concept formation, may be similarly affected. To assess the effect of acute caffeine withdrawal on executive functioning during sleep deprivation, 26 healthy volunteers were administered in double-blind form either repeated doses of caffeine or placebo over two nights of continuous wakefulness. The 108-item Short Category Test was administered after 56 hr. of total sleep deprivation (9 hr. post-caffeine administration). The caffeine group scored significantly more poorly, making approximately 57% more errors on the test than the placebo group. These findings suggest that acute caffeine withdrawal during prolonged sleep deprivation has an adverse effect on abstract reasoning and concept formation.