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Though extended night-time sleep mostly reduces the ‘afternoon dip’, little is known about evening benefits to alertness, or about comparisons with an afternoon nap or caffeine. Twenty healthy carefully screened adults, normal waking alertness levels, underwent four counterbalanced conditions: usual night sleep; night sleep extended<90 min (usual bed-time); up to 20 min afternoon nap; and 150 mg afternoon caffeine (versus decaffeinated coffee). Sleepiness was measured by afternoon and evening multiple sleep latency test (MSLTs), longer psychomotor vigilance test (PVT) sessions and a subjective sleepiness scale. Sleep was extended by average of 74 min, and all participants could nap 15–20 min. Sleep extension had little effect on PVT determined modest levels of morning sleepiness. Afternoon and evening MSLTs showed all active treatments significantly reduced the ‘dip’, with nap most effective until mid-evening; next effective was caffeine, then extension. Late evening sleepiness and subsequent sleep did not differ between conditions. Arguably, participants may have experienced some ‘sleep debt’, given they extended sleep and reflected some sleepiness within settings sensitive to sleepiness. Nevertheless, extended sleep seemed largely superfluous and inefficient in reducing modest levels of sleepiness when compared with a timely nap, and even caffeine. Sleep, such as food and fluid intakes, can be taken to excess of real biological needs, and for many healthy adults, there is a level of modest daytime sleepiness, only unmasked by very sensitive laboratory measures. It may reflect a requirement for more sleep or simply be within the bounds of normal acceptability. [ABSTRACT FROM AUTHOR]

Caffeine is the most widely used stimulant to counteract sleepiness. However, little is known about any placebo effect of caffeine in sleepy people and the effect of suggestibility. Over a 95 min test period, and in a counterbalanced design, 16 young healthy adults underwent 3 × 30 min sessions at the psychomotor vigilance test (PVT), during an early afternoon ‘dip’ enhanced by a prior night's sleep restriction (5 h). On both occasions they were given a cup of a decaffeinated coffee; once when the participant was verbally primed to suggest the coffee was caffeinated (Placebo) and on the other under neutral priming (Control). There were significantly fewer lapses and shorter reaction times following Placebo, for the initial two 30 min sessions, indicating that suggestion about consuming caffeine was effective in improving performance in moderately sleepy people. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The extent to which sleepy drivers are aware of sleepiness has implications for the prevention of sleep-related crashes, especially for drivers younger than 30 years old who are most at risk. Using a real car interactive simulator, we report on EEG, subjective sleepiness, and lane drifting (sleepiness-related driving impairment) from 38 sleep-restricted, healthy young adults undergoing nontreatment control conditions from three (unpublished) investigations using the same experimental protocols for assessing various drinks intended to alleviate sleepiness. Participants drove 2 h during midafternoon under monotonous conditions. For all studies, subjective sleepiness and EEG activity indicative of sleepiness were highly correlated, with both changing concomitantly, along with lane drifting. Drivers had knowledge of their physiological sleepiness. There were indications that sugar content of these drinks may additionally affect sleepiness. [ABSTRACT FROM AUTHOR]

Investigates the effectiveness of 200 milligrams of caffeine in preventing early morning driver sleepiness. Prevalence of sleep-related vehicle accidents in the early morning; Reduction in driving incidents in the first 30 minutes and subjective sleepiness in the first hour after caffeine intake.

Previous research has shown that caffeine and a<15-min nap effectively and separately reduce sleepiness in drivers for 1 hr. in the present study, we examined in 12 sleepy individuals the treatments combined, taken during a 30-min break, prior to a longer (2 hr) continuous monotonous afternoon drive in a car simulator. Nonnap comparisons were 200 mg caffeine only and placebo. For placebo, driving incidents, subjective and electroencephalographic measures of sleepiness all reflected a mid-afternoon peak. This peek was significantly reduced by caffeine and eliminated by the combined treatment, which reduced incidents to 9% of placebo levels versus 34% of placebo levels for caffeine alone. Naps comprising "nonsleep dozing" were still effective. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: Laboratory-based studies show that drowsiness increases the propensity to become distracted. As this phenomenon has not been investigated in drowsy drivers, we underwent a pilot study under realistic monotonous driving conditions to see if distraction was more apparent when drowsy; if so, how does it affect driving performance? Methods: A repeated measures counterbalanced design whereby participants drove for two hours in a fully interactive car simulator during the bi circadian afternoon drive, after a night of either normal (baseline) or restricted sleep to five hours (sleep restriction). Videos of drivers’ faces were analysed blind for short (<3s) and long (>3s) distractions, in which drivers took their eyes off the road ahead. These results were compared with the likelihood of simultaneous lane-drifting incidents, when at least two wheels left the driving lane. Results: More distractions occurred after restricted sleep (p <0.005) for both short and long distractions (p <0.05). There was an overall significant (p <0.02) positive correlation between distractions and driving incidents for both conditions but with significantly more distraction-related incidents after sleep restriction (p <0.03). Conclusions: Following restricted sleep, drivers had an increased propensity to become distracted, which was associated with an increased likelihood of poor driving performance as evidenced by the car leaving the driving lane. [Copyright &y& Elsevier]

Abstract: Young men figure prominently in sleep-related road crashes. Non-driving studies show them to be particularly vulnerable to sleep loss, compared with older men. We assessed the effect of a normal night''s sleep vs. prior sleep restricted to 5h, in a counterbalanced design, on prolonged (2h) afternoon simulated driving in 20 younger (av. 23y) and 19 older (av. 67y) healthy men. Driving was monitored for sleepiness related lane deviations, EEGs were recorded continuously and subjective ratings of sleepiness taken every 200s. Following normal sleep there were no differences between groups for any measure. After sleep restriction younger drivers showed significantly more sleepiness-related deviations and greater 4–11Hz EEG power, indicative of sleepiness. There was a near significant increase in subjective sleepiness. Correlations between the EEG and subjective measures were highly significant for both groups, indicating good self-insight into increasing sleepiness. We confirm the greater vulnerability of younger drivers to sleep loss under prolonged afternoon driving. [Copyright &y& Elsevier]

Abstract: Seemingly, many healthy adults have accrued a sleep debt, as determined by findings based on the multiple sleep latency test (MSLT). However, our recent, extensive survey found self-reported sleep deficit was not linked to daytime sleepiness determined by the Epworth sleepiness scale (ESS). Here, we report on the link between self-reported sleep deficit and gold standard measures of sleepiness: MSLT, Psychomotor vigilance test (PVT) and Karolinska Sleepiness Scale (KSS). Habitual sleep time in forty-three participants, from using a week long sleep diary and actiwatch data, compared with self-ratings of how much sleep they needed, provided estimates of apparent sleep deficit or otherwise. They were split into categories: ‘sleep deficit’ (Av. −47 min), ‘sleep plus’ (Av. 47 min) or ‘neutral’ (Av. 0±15 min), depicting perceived shortfall (or excess) sleep. Although the deficit group desired to sleep longer than the other groups, they actually obtained similar habitual nightly sleep as the neutral group, but less than the sleep plus group. ‘Survival curves’ based on those falling asleep during the MSLT showed no difference between the groups. Neither was there any difference between the groups for the PVT, KSS, or ESS. Here, factors other than sleepiness seem to influence self-perceived sleep deficits. [Copyright &y& Elsevier]