Munehisa Tamaki Department of Behavioral Science, Faculty of Integrated Arts and Sciences, Hiroshima University, 1-7-1, Kagamiyama, Higashihiroshima, 739-8521, Japan.
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.
It is well known that sleepiness occurs and performance declines in the mid-afternoon. Various studies report that a daytime nap in adults improves these impairments.1 On the other hand, it has been proposed that a daytime nap in aged individuals causes their sleep problem, such as, waking in the night and waking in early morning. However, recent studies have reported that there is little relationship between nocturnal sleep and napping,2,3 and that napping is common in healthy aged individuals.4 The purpose of this study is to evaluate the effects of daytime nap on performance, mood and physiological measures in healthy aged individuals. In particular, we studied participants who habitually napped.
Six healthy aged individuals participated in the study. They were initially screened with a modified version of the sleep-health questionnaire5 and were interviewed about their usual sleep. All of them habitually napped in the afternoon three or more times a week and had a good attitude towards the daytime nap (e.g. ‘When I take a nap, I usually feel better afterwards’). The subjects ranged in age between 66 and 78 years old. They were given a detailed description of the study and signed an informed consent. The experiment comprised nap and rest conditions. In the nap condition, the subjects went to bed at 13.00 h and were awakened when 30 min had elapsed from the onset of the sleep stage 1. In this study, a relatively short duration of daytime nap was designed to minimize negative after-effects of nap such as sleep inertia that causes confusion, disorientation and impairment of performance. In the rest condition they took a rest watching a videotape instead of taking a nap. Participants could select a videotape of their choice from the video library. The program was emotionally neutral but not boring. Subjects participated in both conditions with a interval of 1 week.
In both conditions, participants arrived at the laboratory at 09.00 h. Test batteries comprised (i) electroencephalogram (EEG) recordings when relaxed with eyes open and closed; (ii) self-rating of mood; (iii) performance of a visual detection task. These batteries were performed every 30 min from 10.00 to 12.00 h and from 14.00 to 16.00 h. Electroencephalograms were recorded from Fz, Cz, Oz (referred to linked earlobes, τ = 0.3 s) throughout the study except lunch time. Electroencephalogram recordings during the nap were scored by 30-s epochs according to standard sleep stages criteria.6 Blood pressure was recorded before and after taking a nap or a rest lying on the bed. Mood (sleepiness and fatigue) was assessed by a self-rating scale (visual analog scale). The visual detection task was a modified version of the task devised by Englund et al.7 Simple reaction time and percentage correct were used as a performance measure.
Two-way analyses of variance with repeated measures were performed on all of the measures (two conditions × two periods for blood pressure measures, two conditions × eight periods for other measures). The degrees of freedom were adjusted by Greenhouse-Geisser’s epsilon.
Reaction time was shorter in the nap condition than in the rest condition after 14.00 h. Percentage correct increased after taking a nap, but decreased after taking a rest. As for mood measures, subjective sleepiness was lower in the nap condition than in the rest condition after 14.00 h. The main effect of the conditions [F(1/5) = 19.88, P < 0.05] and the interaction [F(2/10) = 5.43, P < 0.05] were significant for subjective sleepiness. Subjective fatigue was constantly maintained from 10.00 to 16.00 h, although it increased remarkably from 14.00 to 16.00 h in the rest condition. The main effect of conditions [F(1/5) = 4.25, P < 0.05] was significant and the interaction [F(2/9) = 3.38, P < 0.08] was almost significant for subjective fatigue. These results showed that the daytime nap had a positive effect upon performance and mood measures.
The EEG α band activity with eyes open increased after taking a rest more than after taking a nap (Fig. 1). This result showed that arousal level was improved by a nap.
In addition, following a nap their diastolic blood pressure (DBP) decreased when compared with the rest condition (Fig. 2). The interaction was significant for DBP [F(1/5) = 4.21, P < 0.05].
The present results showed that performance, mood, EEG arousal and blood pressure in the aged individuals were improved after taking a nap. These results agree with previous studies in adults who take a nap habitually.8,9 However, it had not been sufficiently clear how blood pressure was influenced by a nap. A previous study showed that napping was common in healthy aged individuals.4 The findings of the present study indicate that behavioral, psychological and physiological functions in aged individuals are adequately maintained or facilitated by taking a habitual nap in the mid-afternoon. It is also suggested that taking a nap is an effective strategy for aged individuals to lead a healthy life.
This study was supported in part by the Special Coordination Funds for Promoting Science and Technology of the Science and Technology Agency of the Japanese Government.