Neurobehavioral Correlates of How Time-on-task and Sleep Deprivation Modulate Deployment of Cognitive Effort

Sustaining attention is highly demanding and can falter if there is a shift in willingness to exert effort. Motivated attentional performance and effort preference were tracked in relation to increasing time-on-task (Experiment 1) and sleep deprivation (Experiment 2). Performance decrement with time-on-task was attenuated with reward, while preference to deploy effort decreased with longer task duration. Sleep deprivation, accentuated performance decline with time-on-task, and was accompanied by greater effort-discounting. Motivated attention performance was associated with higher fronto-parietal activation, in both normal and sleep deprived conditions. However, after sleep deprivation modulation of activation by reward was reduced in the anterior cingulate cortex (ACC) and left anterior insula (aIns). Together, these results depict how motivational decline affects performance when one gets tired after sustained task performance and/or sleep deprivation.

Daytime napping after a night of sleep loss decreases sleepiness, improves performance, and causes beneficial changes in cortisol and interleukin-6 secretion

Sleep loss has been associated with increased sleepiness, decreased performance, elevations in inflammatory cytokines, and insulin resistance. Daytime napping has been promoted as a countermeasure to sleep loss. To assess the effects of a 2-h midafternoon nap following a night of sleep loss on postnap sleepiness, performance, cortisol, and IL-6, 41 young healthy individuals (20 men, 21 women) participated in a 7-day sleep deprivation experiment (4 consecutive nights followed by a night of sleep loss and 2 recovery nights). One-half of the subjects were randomly assigned to take a midafternoon nap (1400–1600) the day following the night of total sleep loss. Serial 24-h blood sampling, multiple sleep latency test (MSLT), subjective levels of sleepiness, and psychomotor vigilance task (PVT) were completed on the fourth (predeprivation) and sixth days (postdeprivation). During the nap, subjects had a significant drop in cortisol and IL-6 levels ( P < 0.05). After the nap they experienced significantly less sleepiness (MSLT and subjective, P < 0.05) and a smaller improvement on the PVT ( P < 0.1). At that time, they had a significant transient increase in their cortisol levels ( P < 0.05). In contrast, the levels of IL-6 tended to remain decreased for ∼8 h ( P = 0.1). We conclude that a 2-h midafternoon nap improves alertness, and to a lesser degree performance, and reverses the effects of one night of sleep loss on cortisol and IL-6. The redistribution of cortisol secretion and the prolonged suppression of IL-6 secretion are beneficial, as they improve alertness and performance.

Responses to Confinement: An Investigation of Sensory Deprivation, Social Isolation, Restriction of Movement and Set Factors

An attempt was made to investigate the interactive roles of social isolation, movement restriction, and prior information in the sensory deprivation experiment. 20 Ss were put into an 8-hr. sensory deprivation condition and 20 other Ss into an 8-hr. social isolation (with sensory stimulation) condition. All Ss were also seen on a non-confined control day in the laboratory. The order of the control and experimental days was counterbalanced within each group. These groups were compared with other groups with less movement restriction. The results indicated that the interaction between confinement and familiarity-uncertainty set produced psychological stress effects. Sensory deprivation and uncertainty produced “primary-process” effects; movement restriction enhanced these effects and produced additional discomfort and more autonomic arousal.