Nancy L. Grugle

Effects of dextroamphetamine, caffeine and modafinil on psychomotor vigilance test performance after 44 h of continuous wakefulness.

Prolonged sleep loss impairs alertness, vigilance and some higher‐order cognitive and affective capacities. Some deficits can be temporarily reversed by stimulant medications including caffeine, dextroamphetamine, and modafinil. To date, only one study has directly compared the effectiveness of these three compounds and specified the doses at which all were equally effective in restoring alertness and vigilance following 64 h of wakefulness. The present study compared the effectiveness of these same three stimulants/doses following a less extreme period of sleep loss (i.e., 44 h). Fifty‐three healthy adults received a single dose of modafinil 400 mg (n = 11), dextroamphetamine 20 mg (n = 16), caffeine 600 mg (n = 12), or placebo (n = 14) after 44 h of continuous wakefulness. After 61 h of being awake, participants obtained 12 h of recovery sleep. Psychomotor vigilance was assessed bi‐hourly during waking and following recovery sleep. Relative to placebo, all three stimulants were equally effective in restoring psychomotor vigilance test speed and reducing lapses, although the duration of action was shortest for caffeine and longest for dextroamphetamine. At these doses, caffeine was associated with the highest percentage of subjectively reported side‐effects while modafinil did not differ significantly from placebo. Subsequent recovery sleep was adversely affected in the dextroamphetamine group, but none of the stimulants had deleterious effects on postrecovery performance. Decisions regarding stimulant selection should be made with consideration of how factors such as duration of action, potential side‐effects, and subsequent disruption of recovery sleep may interact with the demands of a particular operational environment.

Gambling When Sleep Deprived: Don't Bet on Stimulants

Recent evidence suggests that sleep deprivation leads to suboptimal decision-making on the Iowa Gambling Task (IGT), a pattern that appears to be unaffected by moderate doses of caffeine. It is not known whether impaired decision-making could be reversed by higher doses of caffeine or by other stimulant countermeasures, such as dextroamphetamine or modafinil. Fifty-four diurnally active healthy subjects completed alternate versions of the IGT at rested baseline, at 23 and 46 h awake, and following a night of recovery sleep. After 44 h awake, participants received a double-blind dose of caffeine (600 mg), dextroamphetamine (20 mg), modafinil (400 mg), or placebo. At baseline, participants showed a normal pattern of advantageous performance, whereas both sleep-deprived sessions were associated with suboptimal decision-making on the IGT. Following stimulant administration on the second night of sleep deprivation, groups receiving caffeine, dextroamphetamine, or modafinil showed significant reduction in subjective sleepiness and improvement in psychomotor vigilance, but decision-making on the IGT remained impaired for all stimulants and did not differ from placebo. Decision-making returned to normal following recovery sleep. These findings are consistent with prior research showing that sleep deprivation leads to suboptimal decision-making on some types of tasks, particularly those that rely heavily on emotion processing regions of the brain, such as the ventromedial prefrontal cortex. Moreover, the deficits in decision-making were not reversed by commonly used stimulant countermeasures, despite restoration of psychomotor vigilance and alertness. These three stimulants may restore some, but not all, aspects of cognitive functioning during sleep deprivation. (Author correspondence: Killgore@mclean.harvard.edu)

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.

The Effects of Modafinil, Caffeine, and Dextroamphetamine on Judgments of Simple Versus Complex Emotional Expressions Following Sleep Deprivation

Cognitive abilities such as vigilance, attention, memory, and executive functioning can be degraded significantly following extended periods of wakefulness. Although much evidence suggests that sleep-loss induced deficits in alertness and vigilance can be reversed or mitigated by stimulants such as caffeine, it is not clear how these compounds may affect other higher level cognitive processes such as emotional perception and judgment. Following 47 h of sleep deprivation, the study examined the effect of three stimulant medications (modafinil 400 mg, dextroamphetamine 20 mg, caffeine 600 mg) or placebo on the ability of 54 healthy participants to discriminate and label simple emotional expressions versus complex affect blends (created by morphing photographs of two different affective facial expressions). For simple affective faces, neither sleep loss nor stimulant medications made any difference on the accuracy of judgments. In contrast, for complex emotion blends, all three stimulant medications significantly improved the ability to discriminate subtle aspects of emotion correctly relative to placebo, but did not differ from one another. These findings suggest that all three stimulant medications are effective at restoring some aspects of subtle affective perception.

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.

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.

Handedness correlates with actigraphically measured sleep in a controlled environment.

The relationship between hand preference and duration of sleep was assessed in 40 healthy subjects using self-report estimates, sleep diaries, and wrist activity monitors during an uncontrolled 7-day at-home phase and during a controlled overnight stay in a sleep laboratory. Handedness was unrelated to any index of sleep duration when assessed in the unregulated home environment. In the controlled environment of the laboratory, however, greater right-hand dominance was positively correlated with more minutes of obtained sleep and greater sleep efficiency. Findings were consistent with previous reports which suggest measures of brain lateralization may be related to sleep and health but further suggest that these relationships may be easily obscured by extraneous environmental factors when assessed in an uncontrolled setting.

Refining the Walter Reed Sleep Management System: An Exemplar for Systems Improvement Using a Macroergonomic Approach

Sleep deprivation, by impairing performance capacity, threatens health and safety across both civilian and military sectors. The Walter Reed Army Institute of Research (WRAIR) has developed a sleep management system (SMS) which provides a sociotechnical template for research in this area. A literature review was conducted to lay the groundwork for development of additional empirical research studies relative to sleep deprivation in order to further develop the sleep management system. Based on the existing body of knowledge regarding sleep deprivation effects on cognitive performance, and based on the ongoing development of the sleep management system, we suggest that a macroergonomic or sociotechnical systems approach to intervention may be useful in optimizing health and safety performance. This paper reviews the pertinent sleep deprivation literature and outlines the important issues for a macroergonomic research agenda.