Jim Horne

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.

Vehicle accidents related to sleep: a review.

Falling asleep while driving accounts for a considerable proportion of vehicle accidents under monotonous driving conditions. Many of these accidents are related to work--for example, drivers of lorries, goods vehicles, and company cars. Time of day (circadian) effects are profound, with sleepiness being particularly evident during night shift work, and driving home afterwards. Circadian factors are as important in determining driver sleepiness as is the duration of the drive, but only duration of the drive is built into legislation protecting professional drivers. Older drivers are also vulnerable to sleepiness in the mid-afternoon. Possible pathological causes of driver sleepiness are discussed, but there is little evidence that this factor contributes greatly to the accident statistics. Sleep does not occur spontaneously without warning. Drivers falling asleep are unlikely to recollect having done so, but will be aware of the precursory state of increasing sleepiness; probably reaching a state of fighting off sleep before an accident. Self awareness of sleepiness is a better method for alerting the driver than automatic sleepiness detectors in the vehicle. None of these have been proved to be reliable and most have shortcomings. Putative counter measures to sleepiness, adopted during continued driving (cold air, use of car radio) are only effective for a short time. The only safe counter measure to driver sleepiness, particularly when the driver reaches the stage of fighting sleep, is to stop driving, and--for example, take a 30 minute break encompassing a short (< 15 minute) nap or coffee (about 150 mg caffeine), which are very effective particularly if taken together. Exercise is of little use. CONCLUSIONS: More education of employers and employees is needed about planning journeys, the dangers of driving while sleepy, and driving at vulnerable times of the day.

Falling asleep whilst driving: are drivers aware of prior sleepiness?

Abstract Falling asleep at the wheel is a common cause of road accidents, but little is known about the extent to which drivers are aware of their sleepiness prior to such accidents. It is an area with medico-legal implications. To simulate this situation 28 healthy young adult experienced drivers, sleep restricted the night before drove for 2 h in the afternoon in an interactive real-car simulator incorporating a dull and monotonous roadway. Lane drifting, typifying sleepy driving, was subdivided into minor and major incidents, where the latter was indicative of actually falling asleep. A distinction was made between the subjective perceptions of sleepiness and the likelihood of falling asleep which drivers reported separately. Increasing sleepiness was closely associated with an increase in the number of incidents. Major incidents were preceded by self-awareness of sleepiness well beforehand and typically, subjects reached the stage of fighting sleep when these incidents happened. Whilst the perceived likelihood of falling asleep was highly correlated with increasing sleepiness, some subjects failed to appreciate that extreme sleepiness is accompanied by a high likelihood of falling asleep. It was not possible for our subjects to fall asleep at the wheel and have an “accident” without experiencing a sustained period of increasing sleepiness, of which they were quite aware. There is a need to educate at least some drivers that extreme sleepiness is very likely to lead to falling asleep and a high accident risk.

Sleep loss impairs short and novel language tasks having a prefrontal focus.

Most cognitive tests administered during sleep loss are well rehearsed to remove practice effects. This can introduce tedium and a loss of novelty, which may be the key to the tests subsequent sensitivity to sleep loss, and why it may need only a few minutes administration before sleep loss effects are apparent. There is little evidence to show that any of these tests are actually affected by sleep loss if given de novo, without practice, but using a non‐sleep deprived control group. Although the sleep deprivation literature advocates that short, novel and stimulating tests would not be expected to be sensitive to sleep loss, recent sleep loss findings using neuropsychological tests focussing on the prefrontal cortex, indicate that such tests may challenge this maxim. Twenty healthy young adults were randomly assigned to two groups: nil sleep deprivation (control), and 36h continuous sleep deprivation (SD). Two, novel, interesting and short (6 min) language tests, known (by brain imaging) to have predominantly a PFC focus, were given, once, towards the end of SD: (i) the Haylings test – which measures the capacity to inhibit strong associations in favour of novel responses, and (ii) a variant of the word fluency test – innovation in a verb‐to‐noun association. Subjects were exhorted to do their best. Compared with control subjects both tasks were significantly impaired by SD. As a check on the effects on the Haylings test, a repeat study was undertaken with 30 more subjects randomly divided as before. The outcome was similar. Linguistically, sleep loss appears to interfere with novel responses and the ability to suppress routine answers.

Individual differences in human circadian rhythms

Research into individual differences in circadian rhythms is reviewed, particularly morningness-eveningness. It was hypothesised that extraverts would be inclined towards eveningness and introverts towards morningness. Forty-eight subjects took regularly their oral temperature. Peak times were identified from smoothed temperature curves. Results showed that extraverts had a peak time insignificantly later than introverts. Re-grouping of the data into the morningness-eveningness dimension, based upon the results of a self assessment questionnaire, showed that evening types had significantly later peak times than morning types. Morningness-eveningness was not significantly ocrrelated with extraversion-introversion, although there was a trend. No significant differences were found for sleep lengths with either groupings, or for sleep-wake habits within extraversion-introversion. Morning types retired and arose significantly earlier than evening types. Although sleep-wake habits and extraversion-introversion help to determine peak times there are other contributory factors to peak time which appear to be partly covered by the questionnaire.

Fatigue, alcohol, and serious road crashes in France: factorial study of national data

Editorial by Feyer France has a high rate of road traffic crashes.1 Although driver fatigue may be an important factor,2–4 it has not been investigated in France, and no comparisons have been made with alcohol related crashes.5 We investigated the role of fatigue in serious road crashes using the French national database.1 We obtained data from the French Ministry of Transport on all road crashes during 1994–8 (640 670) in which at least one person was severely injured (confirmed by paramedics) or died. Crashes were attended by police officers, who completed a standard ministry questionnaire that covered time of incident, location, road and weather conditions, vehicles involved, mechanical defects, health of driver, and alcohol consumption as well as giving summaries of interviews and probable causes. As crashes related to fatigue can be difficult …

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.

Early morning driver sleepiness: Effectiveness of 200 mg caffeine

Sleep-related vehicle accidents are prevalent early morning, especially in younger drivers. In two independent studies following a night of either restricted or nil sleep, young experienced drivers drove for 2 hr (0600-0800 h) continuously in an immobile car on an interactive, computer-generated, dull, and monotonous roadway. This exercise followed ingestion (at 0530 h) of 200 mg caffeine (= 2-3 cups coffee) versus placebo, counterbalanced, double blind. Driving incidents (lane drifting), subjective sleepiness, and 4-11 Hz electroencephalogram (EEG) activity were logged. In Study 1 (sleeping 0000-0500 h), caffeine significantly reduced incidents and subjective sleepiness throughout the 2-hr drive, and EEG power for the second 30-min period. In Study 2 (no sleep), sleepiness affected all measures profoundly, and driving was terminated after 1 hr. Nevertheless, caffeine reduced incidents significantly for the first 30 min and subjective sleepiness for the hour. This caffeine dose, feasibly taken via coffee, effectively reduces early morning driver sleepiness for about 30 min following nil sleep, and for around 2 hr after sleep restriction.

A review of the biological effects of total sleep deprivation in man

This biologically oriented review attempts to complement earlier and more psychological performance based reviews of total sleep deprivation. Also, the effects of total sleep deprivation are interpreted, here, from a function of human sleep perspective, rather than from the more usual stress viewpoint. It would appear that total sleep deprivation does not produce any major changes in biochemical and physiological measures of somatic functioning. Such a conclusion would not seem to support an hypothesis that human sleep is for body restitution. Although there are equivocal results amongst several of the more psychophysiological measures, EEG does show a pronounced change. This latter finding, together with many reports of psychological performance detriment, would appear to sustain a CNS or cerebral restitutional role for human sleep. However, before definitive conclusions can be drawn from the biochemical and physiological findings of total sleep deprivation, the following qualifications of experimental methodology are made: (1) Apart from sleep loss, many studies have provided unnatural regimes which may have ameliorated possible effects of total sleep deprivation. (2) Most studies are of relatively short duration and may not have been sufficiently long for effects to develop. (3) Measures are often limited in range and depth of analysis. (4) Subjects are mostly fit, young adult, intelligent males and there is little constitutional variability. (5) Reported changes of statistical significance may be of no physiological significance and changes of possible physiological significance may be obscured by statistical procedures. (6) Intervening behavioural variables, such as novelty and anticipation of the sleep deprivation situation, may confound real effects.

High incentive effects on vigilance performance during 72 hours of total sleep deprivation.

Abstract Three matched groups of five subjects, designated sleep deprived with incentive (I), sleep deprived without incentive (NI), no sleep deprivation, no incentive control (C), were run on separate occasions. All underwent 1 2 h of auditory vigilance performance three times per 24 h, following a baseline non-incentive day. During deprivation, group I were given attractive monetary reward for “hits” and were “fined” for false alarms and misses. These stakes were doubled for each successive deprivation day in an attempt to combat the increasing tiredness effects. At the end of deprivation, groups I and NI were allowed 8 h of recovery sleep, and were tested again, without incentive for I. It was found that incentive was able to maintain performance (hits and d′) at baseline levels for up to 36 h of deprivation. Thereafter, although this performance fell, it remained significantly better than that for NI, for a further day only. Despite substantive rewards on the third day, incentive was ineffective. Following the recovery sleep, performance returned to normal. Although no significant time-of-day effects were found in performance during the normal waking hours, it was apparent that the major decline per 24 h occurred through the night, with a levelling off in the day.