Yvonne Harrison

The Impact of Sleep Deprivation on Decision Making: A Review

Few sleep deprivation (SD) studies involve realism or high-level decision making, factors relevant to managers, military commanders, and so forth, who are undergoing prolonged work during crises. Instead, research has favored simple tasks sensitive to SD mostly because of their dull monotony. In contrast, complex rule-based, convergent, and logical tasks are unaffected by short-term SD, seemingly because of heightened participant interest and compensatory effort. However, recent findings show that despite this effort, SD still impairs decision making involving the unexpected, innovation, revising plans, competing distraction, and effective communication. Decision-making models developed outside SD provide useful perspectives on these latter effects, as does a neuropsychological explanation of sleep function. SD presents particular difficulties for sleep-deprived decision makers who require these latter skills during emergency situations.

Sleep Loss and Temporal Memory

Historical evidence suggests that sleep deprivation affects temporal memory, but this has not been studied systematically. We explored the effects of 36 hr of sleep deprivation on a neuropsychological test of temporal memory. To promote optimal performance, the test was short, novel, and interesting, and caffeine was used to reduce “sleepiness”. A total of 40 young adults were randomized into four groups: control + caffeine (Cc), control + placebo (Cp), sleep deprived + caffeine (SDc), and sleep deprived + placebo (SDp). Controls slept normally. Caffeine (350 mg) or placebo were given just prior to testing. The task comprised colour photographs of unknown faces and had two components: recognition memory (distinction between previously presented and novel faces), and recency discrimination (temporal memory), when a previously shown face was presented. An interpolated task, self-ordered pointing, acted as a distraction. Caffeine had no effects within control conditions, but significantly reduced subjective sleepiness in SDc. Recognition was unaffected by sleep deprivation, whereas for recency, sleep deprivation groups scored significantly lower than controls. There was no significant improvement of recency with caffeine in the SDc group. Both sleep deprivation groups had poorer insight into their performance with recency. Self-ordered pointing remained unchanged. In conclusion, sleep deprivation impairs temporal memory (i.e. recency) despite other conditions promoting optimal performance.

The relationship between daytime exposure to light and night‐time sleep in 6–12‐week‐old infants

This project investigated the relationship between exposure to light and 24‐h patterns of sleep and crying in young, healthy, full‐term babies living at home and following a normal domestic routine. Measures included an ankle worn activity monitor, an external light monitor and the Barr Baby Day Diary in which parents recorded periods of sleep, crying, feeding and other behaviours at 5‐min intervals throughout the 24‐h period. Fifty‐six babies (26 males and 30 females) were monitored across three consecutive days at 6, 9 and 12 weeks of age. There was an early evening peak in crying which was associated with reduced sleep at 6 weeks. Across the trials there was a gradual shift towards a greater proportion of sleep occurring at night. Sleeping well at 6 weeks was a good indication of more night‐time sleep at 9 and 12 weeks. Babies who slept well at night were exposed to significantly more light in the early afternoon period. These data suggest that light in the normal domestic setting influences the development of the circadian system.

Lack of Evidence for a Marked Endogenous Component Determining Food Intake in Humans During Forced Desynchrony

In an attempt to investigate the relative importance of endogenous and exogenous factors in determining food intake, 14 healthy subjects were studied while living in an Isolation Unit (where external time cues were absent) for eighteen 28 h “days” (equal to 21 solar days). The subjects were free to spend their waking time as they chose, and they had a free choice of what they ate and when they ate it. The only restrictions were that no naps were allowed in the “daytime,” that some time was required to perform a variety of tests at regular intervals throughout the 18.67 h waking periods, and that any food preparation had to be performed by the subjects themselves. Core (rectal) temperature and activity were monitored throughout, and the subjects answered a questionnaire on their eating habits at 3 h intervals during the waking periods. The questionnaire investigated reasons for eating or not eating a meal during the previous 3 h and, if a meal had been eaten, its type, the factors influencing that choice, and the subjects’ subjective responses (hunger before, enjoyment during, and satiety after) to it. The results were analyzed (two-way ANOVA) in terms of both the imposed day length (the exogenous component) and the free-running period of the temperature rhythm (the endogenous component). Results indicated that by far the main reason for eating/not eating was hunger/lack of hunger rather than factors such as food availability and time-pressure. There were statistically significant effects of time within the imposed waking periods upon the type of meal eaten—“breakfast” tending to be a snack, “lunch” a small hot meal, and the “evening meal” a large hot meal. Hot meals (whether small or large) were associated with more hunger before the meal, more enjoyment of the meal, and a greater degree of satiety afterward than were cold meals. These effects suggest that the individuals adjusted their eating habits to fit in with the imposed wake times. By contrast, the effect of circadian phase upon food intake, the type of meal eaten, and subjective responses to the meal was much weaker, and either statistically nonsignificant (P > 0.10) or only marginally so (0.10 > P > 0.05). For example, a large hot meal was chosen as readily for an “evening meal,” and subjective responses to it were the same, at whatever circadian phase it was eaten. We conclude that food intake during forced desynchronization is dominated by the waking schedule rather than by circadian influences; some of the implications of these findings when eating habits and the metabolism of food are concerned, particularly in night workers, are considered briefly.

Loss of negative priming following sleep deprivation

It has been argued that one night of sleep loss in young healthy adults produces changes similar to that associated with normal, healthy ageing—in particular, that young sleep-deprived adults perform similarly to 60-year-old sleep-satiated adults on some tasks of frontal lobe function. This proposition was examined using a protocol viewed by many to be a direct probe of nonvolitional attention mechanisms associated with frontal lobe function. A negative priming (NP) procedure was used to compare performance between non-sleep-deprived (NSD) and sleep-deprived (SD, 34 hr) young, healthy adults. This protocol allowed for exploration of two theories of the NP effect based on inhibitory or memorial processes. Under conditions believed to facilitate inhibitory processes a normal NP effect was found for NSD(16 ms) and SD (9 ms) participants. Under conditions believed to rely on memorial processes there was no NPeffect following SD, compared with a normal NP effect for NSD participants (11 ms). Distractor interference was also greater following SD. These findings do not suggest a similar pattern of change following sleep loss in healthy young adults to that of normal, healthy, non-sleep-deprived aged groups.

Individual response to the end of Daylight Saving Time is largely dependent on habitual sleep duration

The end of Daylight Saving Time provides a valuable opportunity to study the effects of a small, 1-h shift in local clock time in a naturalistic setting. Previous research suggests a delay in adjusting activity patterns by at least one week, possibly more. This study was designed to investigate the importance of prior sleep habits in predicting adaptation to the new schedule. One hundred and twenty participants completed the Pittsburgh Sleep Diary for six days before and six days after the October, UK transition (2010). A subsample (n = 35) also wore activity watches throughout the study. Adherence to the external clock by adjusting bed times and rise times was apparent on the first night, but difficulties in following this timing on subsequent nights, along with deterioration in sleep latency and efficiency, point to a delay in full adjustment, particularly for those who habitually sleep for less than 7.5 h/night.