Interaction of the alerting effect of noise with partial sleep deprivation and circadian rhythmicity of vigilance

Effects of social stress on performance and strain in complex multiple task environments

While stress has been an important research area in the field of ergonomics, research on social stress and on the combination of stressors is largely lacking. This study examined the effects of social stress on psychological and physiological strain and performance. As an exploratory research question we looked at the combined effects of social stress and noise. Fifty-one male student participants were tested for 2 h using a computer-based simulation of a process control environment with multiple tasks. Social stress (TSST) and noise (80 dB) were varied experimentally. During the task, we repeatedly measured primary and secondary task performance, subjective strain, and psychophysiological strain (cortisol, heart rate). We found a main effect of social stress on physiological strain, both on cortisol and heart rate, but no main effects of social stress on subjective strain and performance. These results suggest that maintaining performance under stress comes at the cost of physiological strain. Practitioner summary: Although the presence of social stress is common at work, little experimental work has been done. Our experiment provides empirical evidence for negative effects of social stress on physiological stress responses while subjective strain and performance decrements could not be detected. Abbreviations: ANOVA: analysis of variance; b/min: beats per minute; CAMS: cabin air management system; CO2: carbon dioxide; dB: decibel; Df: degrees of freedom; ECG: electrocardiography; h: hours; Hz: hertz; M: mean; min: minutes; N: sample size; nmol/l: nanomol per liter; O2: oxygen; pm: post meridiem; SD: standard deviation; SE: standard error; sec/s: seconds; TSST: trier social stress test.

The Effects of Exercise as a Countermeasure for Fatigue in Sleep-Deprived Aviators

This study examined the effectiveness of exercise for sustaining performance despite moderate amounts of sleep. Twelve volunteers engaged in 10-min bouts of exercise during one 40-hr period of sleep deprivation and rested for an equivalent amount of time during a 2nd period. Participants were more alert immediately following exercise, as evidenced by longer sleep latencies, than after the resting, control condition. However, electroencephalogram data collected 50 min following exercise or rest showed that exercise facilitated increases in slow-wave activity, signs of decreased alertness. Cognitive deficits and slowed reaction times associated with sleep loss were equivalent in both conditions. The results from this study suggest that short bouts of exercise may ameliorate some of the increases in sleepiness and fatigue associated with sleep loss for a short period of time but are not likely to prevent performance decrements. In addition, less than 1 hr following exercise, significant increases in fatigue and sleepiness may occur.

Sleep inertia

Sleep inertia is a transitional state of lowered arousal occurring immediately after awakening from sleep and producing a temporary decrement in subsequent performance. Many factors are involved in the characteristics of sleep inertia. The duration of prior sleep can influence the severity of subsequent sleep inertia. Although most studies have focused on sleep inertia after short naps, its effects can be shown after a normal 8-h sleep period. One of the most critical factors is the sleep stage prior to awakening. Abrupt awakening during a slow wave sleep (SWS) episode produces more sleep inertia than awakening in stage 1 or 2, REM sleep being intermediate. Therefore, prior sleep deprivation usually enhances sleep inertia since it increases SWS. There is no direct evidence that sleep inertia exhibits a circadian rhythm. However, it seems that sleep inertia is more intense when awakening occurs near the trough of the core body temperature as compared to its circadian peak. A more controversial issue concerns the time course of sleep inertia. Depending on the studies, it can last from 1 min to 4 h. However, in the absence of major sleep deprivation, the duration of sleep inertia rarely exceeds 30 min. But all these results should be analysed as a function of type of task and dependent variables. Different cognitive functions are probably not sensitive to the same degree to sleep inertia and special attention should be provided to dependent variables as a result of the cognitive processes under review. Finally, sleep disorders represent risk factors which deserve new insight in treatment strategies to counteract the adverse effects of sleep inertia.

A specific role for the thalamus in mediating the interaction of attention and arousal in humans

The physiological basis for the interaction of selective attention and arousal is not clearly understood. Here we present evidence in humans that specifically implicates the thalamus in this interaction. We used functional magnetic resonance imaging to measure brain activity during the performance of an attentional task under different levels of arousal. Activity evoked in the ventrolateral thalamus by the attentional task changed as a function of arousal. The highest level of attention-related thalamic activity is seen under conditions of low arousal (secondary to sleep deprivation) compared with high arousal (secondary to caffeine administration). Other brain regions were also active during the attentional task, but these areas did not change their activity as a function of arousal. Control experiments establish that this pattern of changes in thalamic activity cannot be accounted for by nonspecific effects of arousal on cerebral hemodynamics. We conclude that the thalamus is involved in mediating the interaction of attention and arousal in humans.