Mitsuo Hayashi

The effects of a 20 min nap in the mid-afternoon on mood, performance and EEG activity

OBJECTIVE The aim of the study is to examine the effects of a 20 min nap in the mid-afternoon on mood, performance and EEG activities. METHODS Seven young adults who had normal sleep-wake habits without habitual daytime napping participated in the study. They underwent Nap and No-nap conditions at intervals of 1 week. After a nocturnal sleep recording (00:00-08:00 h), their EEG recordings during relaxed wakefulness, and their mood, performance and self-ratings of performance level were measured every 20 min from 10:00 to 18:00 h. For the nap condition, they went to bed at 14:00 h and were awakened when 20 min had elapsed from the onset of sleep stage 1. For the No-nap condition, they took a rest without sleep by sitting on a semi-reclining chair. RESULTS All of the subjects were awakened from sleep stage 2 during the nap. The 20 min nap improved the subjective sleepiness, performance level and self-confidence of their task performance. The nap also suppressed EEG alpha activity during eyes-open wakefulness. CONCLUSIONS The results suggest that a short 20 min nap in the mid-afternoon had positive effects upon the maintenance of the daytime vigilance level.

The alerting effects of caffeine, bright light and face washing after a short daytime nap.

OBJECTIVE The present study examined whether the combination of a short daytime nap with caffeine, bright light and face washing was effective against mid-afternoon sleepiness. METHODS Ten young healthy adults participated in 5 experimental conditions; those experiments were-Nap only: taking a 20 min nap; Caffeine+Nap: taking 200 mg of caffeine followed by a nap; Nap+Bright-light: being exposed to 2000 lx of bright light for 1 min immediately after napping; Nap+Face-washing: washing their faces immediately after napping; and No-Nap: taking a rest without sleep. These naps were taken at 12:40 hours. The subjects engaged in computer tasks for 15 min before napping and for 1 h after napping. RESULTS Caffeine+Nap was the most effective for subjective sleepiness and performance level; its effects lasted throughout 1 h after napping. Nap+Bright-light was comparable with Caffeine+Nap, except for performance level. Nap+Face-washing showed mild and transient effects, however, it suppressed subjective sleepiness immediately after napping. CONCLUSIONS The effects of a short nap against mid-afternoon sleepiness could be enhanced by combining caffeine intake, exposure to bright light, or face washing. SIGNIFICANCE The present study would provide effective countermeasures against mid-afternoon sleepiness and sleepiness related accidents.

The effects of a 20-min nap at noon on sleepiness, performance and EEG activity

The prophylactic effects of a 20-min nap at noon on afternoon sleepiness were studied. Ten young adults who had normal sleep-wake habits without habitual daytime napping were subjected to nap and no-nap conditions at an interval of 1 week. After a nocturnal sleep recording (00.00-08.00 h), their EEG recordings during relaxed wakefulness, mood, performance, and self-ratings of performance level were measured every 20 min from 10.00 h to 18.00 h. For the nap condition, they went to bed at 12.20 h and were awakened when 20 min had elapsed from the onset of sleep stage 1. For the no-nap condition, they rested without sleeping by sitting on a semi-reclining chair. The nap did not improve task performance, however, it improved volition and the self-rating of task performance. It also suppressed subjective sleepiness and attenuated eyes-opened EEG alpha activities. The results suggest that a 20-min nap at noon had partial positive effects on the maintenance of the daytime arousal level.

Effects of a daytime nap in the aged.

This study evaluated the effects of the daytime nap on performance, mood and physiological measures in aged individuals. Participants were six healthy aged persons (M = 72.2 years old) who habitually napped in the afternoon three or more times a week. They participated under two conditions with an interval of 1 week. In the nap condition, the subjects went to bed at 13:00 h and slept for 30 min. In the rest condition, they just watched television. In both conditions, electroencephalogram (EEG), blood pressure, mood and performance were measured before and after a nap or rest. The daytime nap improved performance, decreased subjective sleepiness and fatigue, and attenuated EEG alpha band activity. Moreover, following a nap diastolic blood pressure significantly decreased. These findings suggest that a habitual daytime nap helps aged individuals to maintain their daytime physiological, psychological and behavioral arousal at an adequate level.

Changes in Alpha Band Eeg Activity in the Frontal Area after Stimulation with Music of Different Affective Content

This study investigated the stimulating effects of music. Twelve-channel EEGs (Fp1, Fp2, F7, F8, Fz, C3, C4, Pz, T5, T6, O1, O2) were recorded on 10 students during periods of baseline, premusic rest, music (stimulating or calming), and postmusic rest. The amplitude of the alpha-2 (9.6 to 11.4 Hz) band was lower during the rest session than that during the baseline session. In the music period the amplitude of alpha-2 band increased during both the stimulating and calm music. The frontal interhemispheric coherence values (F7-F8) of the alpha-2 band increased during the stimulating music session, while the coherence values did not change during the calm music. These findings implied close relationships between the interhemispheric transmission of information in the frontal areas and positive attention to stimulating music.

Event-related potentials elicited by wrong terminal notes: effects of temporal disruption.

Wrong terminal notes of familiar musical phrases are known to elicit a large positive deflection of the event-related potential (ERP). The present study examined whether the effect of wrong terminal notes on ERP was modulated by the timing of their occurrence. Sixteen non-musicians were asked to rate the congruity of the endings of 50 well-known musical phrases. Four different types of endings were made for each phrase by manipulating the timing (well-timed vs. delayed for 750 ms) and pitch (correct vs. wrong) of the last note orthogonally. These ending patterns were presented equiprobably in an unpredictable order. Wrong notes elicited large late positive waves irrespective of the timing of occurrence. When the notes were delayed, however, the positive waves were reduced in amplitude to about 50% of those elicited by well-timed notes. These results suggest that the temporal (rhythmic) structure of musical phrases strongly influences the processing of melodic information.

Effects of Self-Awakening on Sleep Structure of a Daytime Short Nap and on Subsequent Arousal Levels

To investigate the effects of self-awakening on sleep structure and daytime arousal after a short nap, a within-subjects comparison was made of participants in self-awakening and forced-awakening conditions. In the self-awakening condition, participants were instructed to wake up by themselves 15 min. after the experimenter turned the lights off. In the forced-awakening condition, the experimenter awakened them 20 min. after the lights were turned off. To control the maximum sleep time for the two conditions, we used different instructions in each condition. Participants were 10 healthy college students. Their physiological arousal and subjective sleepiness were evaluated using the P300 amplitude of the auditory event-related potential (ERP) and the visual analog scale previously described by Monk and Kathryn, et al. For evaluating sleep structure during the nap, Horis 1994 hypnagogic EEG stages were used. P300 amplitude was significantly lower, and subjective sleepiness was significantly higher after forced-awakening than self-awakening, indicating that arousal was higher after self-awakening. The EEGs during napping in the forced-awakening condition indicated deeper sleep. Given this deeper sleep, severe sleep inertia occurred after the forced-awakening condition. In conclusion, it appeared a short nap with self-awakening was more effective in reducing a post-lunch dip than one with forced-awakening.

Short nap versus short rest: recuperative effects during VDT work

The effects of a 20-min nap during 2 h of visual display terminal (VDT) work were examined. Ten young healthy adults took a 20-min nap or a 20-min rest 1 h after VDT work, followed by another 1 h of VDT work. A 20-min rest temporarily restored subjective sleepiness, but it deteriorated during the additional 1 h of work. In contrast, a 20-min nap maintained subjective alertness and performance level at a higher level and mental fatigue at a lower level for the additional 1 h of work. These results suggest that a short nap would be useful to both fatigue recovery and fatigue prevention during continuous VDT work. The present findings may provide a new work/rest strategy.

Auto power and coherence analysis of delta-theta band EEG during the waking-sleeping transition period.

To evaluate the spatio-temporal variation of delta and theta band EEGs during the waking-sleeping transition period, auto power and coherence analyses of scalp EEGs were carried out on 12 male subjects. The 7 auto power and 21 coherence values obtained from the 7 areas were studied every 20 s from 5 min before stage 1 onset to 24 min after stage 1 onset. The consecutive samples of spectra were computed for two frequency bands (delta: 2.5-3.5 Hz; theta: 4.0-7.5 Hz). Auto power started to increase after stage 1 onset and terminated 8.4 min after stage 2 onset. Topograms of each band power changed with progression towards deep sleep from the flat or relatively low voltage pattern without any focus to the frontopolar-parietal pattern or the fronto-parietal dominant pattern. Principal component analysis of the coherence values revealed generalized and localized components in each band. The generalized component was distributed across scalp areas, while the localized component was distributed in frontopolar-frontal areas. The generalized component decreased to the plateau level of non-rapid eye movement (NREM) sleep 5.4 min after stage 2 onset. The localized component started to increase after stage 1 onset and reached the plateau level of NREM sleep 2.4 min after stage 2 onset. These results indicate that the delta-theta band EEG structures of the waking-sleeping transition period may not be uniform across the scalp areas and the hypnagogic period may start after stage 1 onset and continue for 8.4 min after stage 2 onset.

Circasemidian 12 h cycle of slow wave sleep under constant darkness.

OBJECTIVES Afternoon sleepiness is a widespread phenomenon. The present study aimed to test Broughtons hypothesis (Sleep and alertness: chronobiological, behavioral, and medical aspects of napping. New York, NY: Raven Press, 1989. p. 71-98) that afternoon sleep propensity might reflect the circasemidian 12h cycle of slow wave sleep (SWS). METHODS Nine subjects (21-27 year) stayed alone under constant darkness (0 lux) without social contact for 72 h. They were allowed to sleep and eat freely. Their polysomnograms during 72 h of constant darkness were analyzed. RESULTS The total sleep time (TST) accounted for 41.6h (57.9%) of the 72 h and decreased progressively as a function of time. The reduction in TST was dependent on the decrease in sleep stage 2 and rapid eye movement (REM) sleep. The amount of SWS did not significantly change among the days. The circadian (1 cycle/day) and circasemidian (2cycles/day) cycles were observed in SWS. Those accounted for 13.9 and 11.1% of the total variance, respectively. SWS during the time corresponding to daytime occurred 9-10h before and 15-16 h after the nocturnal sleep gate. In addition, weak but significant correlations were observed between the amounts of SWS and the waking time before the sleep episodes (r=0.332) and prior REM sleep (r=-0.236). CONCLUSIONS The present findings suggest that SWS might occur not only always in a homeostatic manner as a function of prior wakefulness, but also as a circasemidian rhythmic function.