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.

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.

Lack of degradation in visuospatial perception of line orientation after one night of sleep loss.

Sleep deprivation impairs a variety of cognitive abilities including vigilance, attention, and executive function. Although sleep loss has been shown to impair tasks requiring visual attention and spatial perception, it is not clear whether these deficits are exclusively a function of reduced attention and vigilance or if there are also alterations in visuospatial perception. Visuospatial perception and sustained vigilance performance were therefore examined in 54 healthy volunteers at rested baseline and again after one night of sleep deprivation using the Judgment of Line Orientation Test and a computerized test of psychomotor vigilance. Whereas psychomotor vigilance declined significantly from baseline to sleep-deprived testing, scores on the Judgment of Line Orientation did not change significantly. Results suggest that documented performance deficits associated with sleep loss are unlikely to be the result of dysfunction within systems of the brain responsible for simple visuospatial perception and processing of line angles.

The effects of caffeine, dextroamphetamine, and modafinil on humor appreciation during sleep deprivation.

STUDY OBJECTIVES: Sleep loss consistently impairs performance on measures of alertness, vigilance, and response speed, but its effects on higher-order executive functions are not well delineated. Similarly, whereas deficits in arousal and vigilance can be temporarily countered by the use of several different stimulant medications, it is not clear how these compounds affect complex cognitive processes in sleep-deprived individuals. DESIGN: We evaluated the effects of double-blind administration of 3 stimulant medications or placebo on the ability to appreciate humor in visual (cartoons) or verbal (headlines) stimuli presented on a computer screen following 49.5 hours of sleep deprivation. SETTING: In-residence sleep-laboratory facility at the Walter Reed Army Institute of Research. PARTICIPANTS: Fifty-four healthy adults (29 men, 24 women), ranging in age from 18 to 36 years. INTERVENTIONS: Each participant was randomly assigned to 1 of 3 stimulant medication groups, including caffeine, 600 mg, n = 12; modafinil, 400 mg, n = 11; dextroamphetamine, 20 mg, n = 16; or placebo, n = 14. MEASUREMENTS AND RESULTS: Humor appreciation for cartoon stimuli was enhanced by modafinil relative to both placebo and caffeine, but there was no effect of any stimulant medication on the appreciation of verbal humor during sleep loss. In contrast, all 3 stimulants improved psychomotor response speed, whereas only caffeine and dextroamphetamine improved ratings of subjective sleepiness. CONCLUSIONS: Findings suggest that, despite similar alerting and vigilance-promoting effects, these 3 compounds have significantly different effects on those highly complex cognitive abilities mediated by the pre-frontal cortex.

Odor identification accuracy declines following 24 h of sleep deprivation.

Brain imaging studies demonstrate that sleep deprivation reduces glucose metabolism and blood flow in the prefrontal cortex, and such reductions are associated with impairments in cognitive functioning. Although some of the greatest metabolic declines occur within the orbitofrontal cortex, little is known about the effects of sleep loss on the types of processes mediated by this region, including emotion, motivation, feeding, and olfaction. The present study tested odor identification accuracy when individuals were well rested and again following 24 h of wakefulness. Relative to rested baseline performance, sleep-deprived individuals demonstrated a significant decline in the ability to identify specific odors on the Smell Identification Test. This decrement in olfactory functioning occurred concomitantly with slowed psychomotor speed and increased ratings of self-reported sleepiness. Performance on a task that required complex mental set shifting did not change significantly following sleep deprivation, suggesting that the decrements in odor identification could not be attributed to task difficulty. Finally, while there was no relationship between subjective sleepiness and odor identification at rested baseline, greater subjective sleepiness was associated with better odor identification ability following 24 h of sleep loss. Possible implications of these findings are discussed.

Effects of the periodic administration of odor or vibration on a 3-hr. vigilance task.

The present study examined performance during 3 hr. of simulated sentry duty with and without the intermittent administration of low-level sensory stimuli (odor or vibration). For odor and control conditions, target-detection latency increased steadily over the course of the 3-hr. session. Administration of a tactile stimulus reduced the increase in detection latency compared to that found in odor and control conditions. For all conditions, there were no significant differences in target-detection frequency, shot accuracy, or friend-foe discrimination. Across all conditions, restlessness (motor activity) increased significantly the first hour and remained elevated for the rest of the session. Subjective measures of workload (NASA-TLX) indicated that the 3-hr. task rated high on physical demand, mental demand, frustration, and overall workload. These findings suggest that the intermittent delivery of a clearly detectable tactile stimulus can reduce reaction-time decrements that occur as time on task increases.