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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]

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. [ABSTRACT FROM AUTHOR]

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]