A Short Nap and Natural Bright Light Exposure Improve Positive Mood Status

Transcription

1 Industrial Health 2007, 45, Original Article A Short Nap and Natural Bright Light Exposure Improve Positive Mood Status Kosuke KAIDA*, Masaya TAKAHASHI and Yasumasa OTSUKA National Institute of Occupational Safety and Health, Nagao, Tama-ku, Kawasaki, Kanagawa , Japan Received June 19, 2006 and accepted December 4, 2006 Abstract: While the effects of a short nap on performance and arousal level have been well investigated, less attention has been paid to its effects on mood status. The aim of the present study was to examine the effects of a short nap and natural bright light exposure on mood status. Participants were 16 healthy females who were on average 38.1 (SD = 2.68) yr old. From 11:00 to 12:00, the participants carried out a set of tasks twice with baseline lighting (<100 lux). From 12:40 to 13:10, they were subjected to three experimental conditions: control (<100 lux), natural bright light (>2,000 lux), and a 20-min nap. From 13:10 to 16:10, the tasks were repeated six times with the baseline lighting. To measure mood status, multiple visual analogue scales (to measure anxiety, sadness, anger, confusion, apathy, fatigue, and sleepiness) and the Mood Check List 3 (MCL-3) (to derive pleasantness, satisfaction and relaxation ) were employed. The results showed that brief (30 min) natural bright light exposure improved one dimension of mood status, pleasantness. A short nap also improved dimensions of mood status ( pleasantness, satisfaction, and relaxation ). These results suggest that the proper application of both natural light and a short nap shifts the mood status to the positive/favorable side. Key words: Natural bright light, Short daytime nap, Sleep, Sleepiness, Mood status Introduction A short nap and bright light exposure are well recognized as countermeasures against accidents or mistakes caused by sleepiness in various occupational situations such as car driving 1) and night shift work 2, 3). As a number of studies suggest 4 21), their positive effects on performance and arousal level seem to be evident. While the effects of a short nap on performance and arousal level have been well investigated, less attention has been paid to its effects on mood status. Given that subjective mood and job satisfaction influence each other 22), and job satisfaction relates to job performance, absenteeism and turnover, it is important to know the effects of a short nap and bright light on mood status. So far, several studies have examined subjective mood *To whom correspondence should be addressed. after a short nap 6, 9, 11, 23). Our previous questionnaire survey of the elderly (>65 yr) 24) suggested the positive effect of a short nap on mood status; i.e. a regular short nap habit was associated with higher self-efficacy, compared to an irregular one. Additionally, Milner et al. have recently reported that a short nap shifts subjective mood to the positive side, e.g. sad to happy or sluggish to energetic 25). These reports indicate the positive effects of a short nap on mood status, but more evidence needs to be accumulated. Similar positive effects on performance and mood have also been reported for bright light exposure. For example, Phipps-Nelson et al. reported that daytime exposure to bright light (1,000 lux) reduced subjective sleepiness and improved performance 14). Rüger et al. reported that 4-h bright light exposure suppressed increasing sleepiness and fatigue in the afternoon and at midnight, and that it might also improve energy status 17). Although the result of the energy status did not reach a statistically significant level 17), their hypothesis

2 302 K KAIDA et al. is plausible. In fact, a number of studies have asserted that bright light can be used for the treatment of depression or seasonal affective disorders 26). An intervention study found that repeated daytime bright light exposure improved vitality and reduced depressive symptoms in healthy people 15). The aim of the present study was to examine the effects of a short nap and bright light exposure on various mood statuses. For this purpose, the study employed multiple visual analogue scales (to measure anxiety, sadness, anger, confusion, apathy, fatigue, and sleepiness) and the Mood Check List 3 (MCL-3) (to derive pleasantness, satisfaction, and relaxation ) 27). We hypothesized that (1) a short nap would not only reduce subjective sleepiness and fatigue but also shift the mood status to the positive/ favorable side, and that (2) bright light would reduce subjective sleepiness and fatigue and also increase positive mood status during the exposure. Some of the results of the present study, those which examine the effects on the physiologic arousal level, have already been reported 28). Methods Participants and design The participants were 16 healthy female paid volunteers aged 33 to 43 yr (average, 38.1 ± 2.68 yr). Only females were selected for the present study because it was difficult to find a male participant who met the selection criteria. All of the participants met the following criteria: (1) a normal sleep-wake cycle classified as intermediate type according to the Morningness-Eveningness questionnaire 29, 30) ; (2) no report of any physical or mental health problems, and a score <15 on the Center for Epidemiological Studies-Depression Scale (CES-D) 31) ; (3) no experience of shift work within the 3 months prior to the experiment; (4) no travel to a different time zone within the 3 months prior to the experiment; (5) no use of medication; (6) non-smoker, and (7) a body mass index less than 25 (calculated as weight in kilograms divided by the square of the height in meters, BMI). The participants Morningness-Eveningness score, CES-D score, and BMI (mean ± standard deviation) score were 53.8 ± 4.38, 7.2 ± 5.99, and 21.6 ± 2.71 kg/m 2, respectively. The study 28) involved one preparatory day and three experimental days. The preparatory day was used for practicing and making participants accustomed to the experimental circumstances. During the preparatory day, the participants followed the same schedule as that for an experimental day as explained below, except for the explanation of the experiment and the signing of the forms of informed consent which took place during the first session from 11:00 to 11:30. The data obtained from the preparatory day were excluded from the analyses. During the experimental days, the participants arrived at the laboratory at 10:30 a.m. and had electrodes applied. From 11:00 to 12:00 a set of tasks (behavioral and electrophysiological see below) was repeated twice (Sessions 1 and 2) at a light level below 100 lux. During a break from 12:00 to 12:40, lunch was served. From 12:40 to 13:10 (Session 3) the participants experienced experimental conditions that differed among the three days, involving the performance of a set of tasks under two different lighting levels or a nap, each on a separate day. On day 1, the lighting was <100 lux (control condition, CNT); on day 2, the lighting was >2,000 lux (natural bright light condition, NBL); and on day 3, a 20-min nap opportunity was given (with lighting <5 lux, nap condition, NAP). From 13:10 to 16:10, the tasks were repeated six times (i.e., Session 4 to 9) with baseline lighting (<100 lux). Thus, the participants carried out the same task 26 times during the three experimental days (the task was not carried out during the nap). All of the light intensities were measured using an illuminometer (T-10, Konica Minolta Holdings, Inc., Tokyo, Japan) at the eye-level of the participants. The data obtained from Session 1 were excluded from the analyses. Natural bright light entered the experimental room through window glass to avoid the harmful effects of ultraviolet light in it. Participants went home after the experiment and returned to the laboratory the next morning. The participants were requested to refrain from drinking beverages containing caffeine and alcohol during the days of preparation and the experimental days. They were also requested to keep a normal sleep-wake cycle during those days, and their sleepwake cycles at home were monitored using the Actiwatch (Mini Mitter Co., Inc., Bend, Oregon, U.S.A.) and a sleep diary. The lunch served contained (mean ± standard deviation): carbohydrates, 200 ± 0 g; protein, 16.8 ± 3.49 g; fat, 23.2 ± 5.77 g; and had a caloric value of ± 63.8 Kcal. The meal was adjusted for the weight of the participants (52.2 ± 7.42 kg). The experimental protocol was reviewed and approved by the Ethical Committee in Research Involving Humans at the National Institute of Occupational Safety and Health (National Institute of Industrial Health), Japan. Procedure The set of tasks for measuring performance and the arousal Industrial Health 2007, 45,

3 A SHORT NAP, BRIGHT LIGHT AND POSITIVE MOOD STATUS 303 level consisted of the psychomotor vigilance task (PVT) 32) using the Psychomotor Vigilance Task Monitor (PVT-192, Ambulatory Monitoring, Inc., New York, U.S.A.), the Karolinska drowsiness test (KDT) 33), the alpha attenuation test (AAT) 34), the multiple 100 mm visual analogue scale (VAS) 35) for sleepiness, fatigue, apathy, confusion, anger, sadness, and anxiety, and the MCL-3 27). The time schedule of the series of tasks was 10 min for the PVT, 1 min each for the Karolinska sleepiness scale 33), VAS, and MCL-3, 7 min for the KDT, 8 min for the AAT, with 4 min for rest (total: 30 min). The detailed experimental schedule and results, except VAS and MCL-3, reported in other publications 28, 36). Rated subjective mood status The MCL-3 was originally developed for the measures of positive mood status following exercise 27). The MCL-3 scale is composed of 22 items (7-grade Likert scales), which are categorized into three independent factors: pleasantness, relaxation, and satisfaction. Its reliability has been confirmed (Cronbach s α coefficients = 0.959) 27). Pleasantness consists of 14 items (animated/apathetic, refreshed/fatigue, lively/depressed, neat/disorganized, buoyant/dejected, bright/dark, spirited/dispirited, lighthearted/heavy-hearted, pleasant/unpleasant, delighted/ agonized, good-humored/ill humored, relieved/hampered, fulfilled/unfulfilled, clear-headed/foggy), Relaxation consists of 5 items (composed/fidgety, relaxed/tense, comfortable/uncomfortable, peaceful/angry, calm/irritable); and satisfaction of 3 items (happy/unhappy, satisfied/ dissatisfied, cheerful/gloomy). Participants were asked to circle the scale number indicating their feeling at the moment. For the analysis, the items related to the three factors were averaged separately. The VAS was presented on 100-mm lines with 7 dimensions, which were not anxious, not sleepy, not fatigued, vigor, not confused, not angry, and not sad on the left end of the line and anxious, sleepy, fatigued, apathetic, confused, angry, and sad on the right end of the line. These factors were selected from those of the Japanese version of the Profile of Mood States (POMS) 37). Participants were asked to view the lines as representing their personal range of feelings and to place a mark on the line indicating their feeling at the moment. Statistical analysis All of the data were submitted to a Condition (CNT, NBL and NAP) Session (from Sessions 4 to 9) repeated-measures analysis of variance (ANOVA) with the SPSS software system. To control for the type 1 error associated with violation of the sphericity assumption, degrees of freedom greater than one were reduced by the Huynh-Feldt ε correction. The multiple paired t-test with the Bonferroni correction was applied for post-hoc comparisons. Sleep stages during naps were visually scored every 20 seconds according to the criteria of Rechtshaffen and Kales 38). Results Sleep/rest time at night and during the naps Total sleep/rest time measured by the Actiwatch prior to the experimental days was (± 52.56) min for Day 1, (± 49.17) min for Day 2, and (± 53.86) min for Day 3. The variation across days was not significant [F(2, 30) = 1.09, p = 0.92, ε = 0.92]. Total sleep time in the nap Fig. 1. Scores of the Mood Check List (MCL-3). CNT, the control condition; NBL, the natural bright light condition; NAP, the nap condition. a, CNT vs. NBL; b, CNT vs. NAP; c, NBL vs. NAP. Significant levels set at p<0.017 for Sessions 2 and 4, p<0.05 for Session 3.

4 304 K KAIDA et al. Table 1. Scores of the mood check list (MCL-3) and visual analogue scale (VAS) by Condition and Session Session S5 S6 S7 S8 S9 MCL-3 Pleasantness CNT 2.6 (0.56) 2.5 (0.53) 2.6 (0.57) 2.7 (0.60) 2.8 (0.72) NBL 2.6 (0.46) 2.5 (0.52) 2.7 (0.39) 2.7 (0.52) 3.0 (0.44) NAP 2.7 (0.38) 2.6 (0.49) 2.6 (0.43) 2.6 (0.47) 2.9 (0.32) Relaxation CNT 3.8 (0.58) 3.8 (0.46) 3.8 (0.44) 3.6 (0.44) 3.6 (0.62) NBL 3.7 (0.58) 3.8 (0.52) 3.8 (0.43) 3.8 (0.46) 3.7 (0.44) NAP 3.7 (0.66) 3.8 (0.66) 3.8 (0.64) 3.7 (0.68) 3.6 (0.59) Satisfaction CNT 3.0 (0.21) 2.9 (0.32) 3.0 (0.27) 3.0 (0.24) 3.2 (0.53) NBL 2.9 (0.42) 2.9 (0.36) 2.9 (0.29) 3.0 (0.43) 3.1 (0.47) NAP 3.0 (0.29) 2.9 (0.36) 2.9 (0.28) 3.0 (0.36) 3.1 (0.39) VAS Anxiety CNT 5.5 (9.32) 11.6 (23.82) 9.9 (19.82) 8.9 (17.71) 8.5 (13.75) NBL 10.6 (18.10) 13.1 (21.89) 9.5 (18.10) 7.1 (14.41) 7.5 (16.11) NAP 11.7 (21.56) 10.7 (20.70) 12.4 (21.49) 9.5 (15.59) 7.0 (13.93) Sadness CNT 3.9 (5.72) 8.4 (18.55) 10.7 (24.76) 6.5 (14.48) 4.4 (7.08) NBL 11.8 (21.85) 14.3 (24.62) 9.2 (17.56) 5.7 (9.13) 6.0 (9.35) NAP 12.8 (23.20) 13.2 (25.68) 12.8 (24.60) 11.8 (22.56) 7.0 (12.94) Anger CNT 3.6 (5.23) 6.1 (14.86) 8.2 (16.04) 4.3 (6.41) 4.9 (7.26) NBL 5.4 (9.19) 6.9 (14.40) 6.7 (14.75) 6.4 (14.10) 5.6 (10.35) NAP 7.0 (12.89) 4.8 (7.52) 5.0 (8.87) 5.0 (7.82) 3.9 (5.67) Confusion CNT 22.9 (23.66) 27.1 (28.06) 30.3 (29.21) 22.5 (28.21) 25.5 (26.04) NBL 24.2 (25.57) 29.0 (31.95) 27.1 (30.97) 28.8 (33.73) 31.4 (37.95) NAP 25.1 (25.74) 27.0 (28.88) 29.5 (32.36) 28.2 (30.70) 22.0 (30.08) Apathy CNT 33.0 (19.78) 25.4 (18.88) 24.5 (17.40) 35.6 (23.11) 38.5 (21.99) NBL 28.4 (14.37) 24.9 (11.02) 26.9 (17.43) 30.1 (20.70) 40.3 (18.80) NAP 39.1 (19.63) 29.5 (18.65) 27.0 (12.91) 29.1 (18.30) 41.5 (18.20) Fatigue CNT 65.1 (23.21) 66.3 (26.76) 72.5 (23.36) 63.0 (22.40) 65.6 (26.72) NBL 64.2 (17.38) 67.6 (15.41) 74.4 (17.18) 70.0 (17.18) 67.9 (14.65) NAP 61.2 (18.63) 67.6 (16.96) 65.9 (16.66) 69.9 (16.55) 68.2 (13.38) Sleepiness CNT 76.1 (19.35) 82.9 (16.16) 79.8 (18.79) 65.1 (28.56) 60.5 (30.43) NBL 73.1 (16.01) 77.4 (14.82) 74.4 (20.65) 67.4 (27.62) 60.7 (21.06) NAP 67.4 (16.68) 78.1 (16.06) 76.4 (15.36) 68.6 (21.15) 57.1 (27.31) SD s are shown in parentheses. CNT, the control condition; NBL, the natural bright light condition; NAP, the nap condition. condition was 13.0 ± 5.74 minutes. Slow-wave sleep and rapid eye movement sleep did not appear during the naps. Positive mood status (MCL-3) Before the nap/bright light exposure (i.e. Session 2), there was no significant difference among the three conditions in positive mood status as shown in Fig. 1. During Session 3 under bright light exposure, pleasantness was significantly higher than in the CNT condition. Significant interactions were found between Condition and Session in pleasantness and satisfaction from the ANOVA of Sessions 4 to 9 (see Table 2). Post-hoc analysis detected significant differences in Session 4 (i.e., immediately after the nap), in which all three variables were significantly higher in the NAP condition than in the other two conditions. The three positive mood statuses declined as the sessions proceeded. The results of Sessions 2 to 4 are depicted in Fig. 1. Post-hoc analysis for the remaining data did not yield significant outputs. These data and SD are shown in Table 1. Negative mood status (VAS) Before the nap/bright light exposure (i.e., Session 2), there was no significant difference among the three conditions in negative mood status, as shown in Fig. 2. During Session 3, sleepiness was significantly lower in the NBL condition than in the CNT condition. Even though ANOVA yielded no significant main effect Industrial Health 2007, 45,

5 A SHORT NAP, BRIGHT LIGHT AND POSITIVE MOOD STATUS 305 Table 2. Results of the two-way ANOVA Condition Session Interaction F (2, 30) p ε F (5, 75) p ε F (10, 150) p ε MCL-3 Pleasantness 0.56 n.s < < Relaxation 0.50 n.s < n.s Satisfaction 0.22 n.s < < VAS Anxiety 0.26 n.s n.s n.s Sadness 1.62 n.s n.s n.s Anger 0.09 n.s n.s n.s Confusion 0.07 n.s n.s n.s Apathy 0.88 n.s < n.s Fatigue 0.79 n.s < n.s Sleepiness 0.76 n.s < n.s of Condition and no interaction between Condition and Session, the differences among conditions seemed to be clear in Session 4 (see Fig. 2). Thus, the post-hoc analysis was directly applied to Session 4. In Session 4, sleepiness was significantly lower in the NAP condition than in the NBL and CNT conditions. Fatigue and apathy were also significantly lower in the NAP condition than in the NBL condition in Session 4. These three negative mood statuses increased as the sessions proceeded. The results of ANOVA and the post-hoc analysis are shown in Table 2 and Fig. 2, respectively. Discussion The present study has demonstrated that brief (30 min) exposure to natural bright light (>2,000 lux) improved one dimension of positive mood status, pleasantness, and reduced subjective sleepiness, although this immediate effect was limited to the period of light exposure. A short nap also improved dimensions of positive mood status, pleasantness, satisfaction, and relaxation, and reduced subjective sleepiness. These results are compatible with our previous report 28), which demonstrated that bright light exposure and a short nap improved the electrophysiological arousal level. The results suggest that these two interventions could improve mood status and arousal level. The major findings of the present study can be summarized as two issues. First, an immediate effect of natural bright light can be obtained from a brief (30 min) period of exposure in the afternoon. Although previous studies have reported the effects of bright light during day and night 7, 14, 16, 17), most studies kept the participants under bright light for more than 4 h used fluorescent or incandescent lamps rather than natural light for exposure. Second, all three dimensions of positive mood measured by the MCL-3 ( pleasantness, satisfaction, and relaxation ) and subjective sleepiness improved after a short nap. Although it is beyond the topic of the present report, a short nap and natural bright light exposure may be a useful strategy to improve not only mood but also job satisfaction, as noted by Judge and Ilies (2004) who suggested that positive mood improves job satisfaction 22). Given that light temperature rather than its intensity has received considerable interest 39, 40) and that the color temperature of natural light differs between morning and evening, the next research question is the sensitivity to natural light exposure at different times of day (i.e., morning, midday, evening). Although many studies have compared light sensitivity, which varies at different times of day and different color temperatures 41 43), to the best of our knowledge, few studies have investigated its immediate effects on arousal level or mood status. Light sensitivity research may contribute to architectural lighting design and the effective use of natural light in developing optimal economical and ecological occupational environments. The results of the present study on the effect of a short nap on subjective sleepiness is consistent with previous studies 4 6, 9 12, 21, 23, 25). Some studies have reported that subjective fatigue declined after a short nap 4, 12, 25, 44), but others, including the present results, have not 9, 11, 21). This inconsistency may be caused by differences in defining fatigue. Several investigators have employed the terms sleepiness and fatigue interchangeably 45, 46), even though fatigue involves a number of psychosocial and behavioral processes whereas the term sleepiness has a rather precise definition 47).

6 306 K KAIDA et al. In conclusion, the present study confirmed mood improvement due to natural bright light exposure or a short nap. The results suggest that proper application of both natural light and a short nap might make a workplace more comfortable. Acknowledgments The principal author is the recipient of the Japan Society for the Promotion of Science (JSPS) postdoctoral fellowship. We would like to thank Naoko Kaida at Stockholm Environment Institute (SEI) for helpful comments on the manuscript. References Fig. 2. Scores of the multiple visual analogue scale (VAS). CNT, the control condition; NBL, the natural bright light condition; NAP, the nap condition. a, CNT vs. NBL; b, CNT vs. NAP; c, NBL vs. NAP. Significant levels set at p<0.017 for Sessions 2 and 4, p<0.05 for Session 3. The present study did not detect significant deterioration in the subjective mood immediately after the nap (Session 4). As reported earlier 8, 9, 25, 48 50), a 20-min nap is long enough to obtain recuperative effects and short enough to avoid sleep inertia. Moreover, subjective mood and sleepiness after the bright light exposure deteriorated significantly more than after the short nap in Session 4. The acute effect of bright light may not remain after the exposure in the afternoon, when melatonin secretion is at its lowest 43). Thus, a short nap could be preferable to brief bright light exposure to improve arousal levels and mood status in the afternoon. 1) Horne JA, Reyner LA (1996) Counteracting driver sleepiness: effects of napping, caffeine, and placebo. Psychophysiology 33, ) Lowden A, Åkerstedt T, Wibom R (2004) Suppression of sleepiness and melatonin by bright light exposure during breaks in night work. J Sleep Res 13, ) Sallinen M, Härmä M, Åkerstedt T, Rosa R, Lillqvist O (1998) Promoting alertness with a short nap during a night shift. J Sleep Res 7, ) Hayashi M, Chikazawa Y, Hori T (2004) Short nap versus short rest: recuperative effects during VDT work. Ergonomics 47, ) Takahashi M, Arito H (2000) Maintenance of alertness and performance by a brief nap after lunch under prior sleep deficit. Sleep 23, ) Kaida K, Nakano E, Nittono H, Hayashi M, Hori T (2003) The effects of self-awakening on heart rate activity in a short afternoon nap. Clin Neurophysiol 114, ) Thorn L, Hucklebridge F, Esgate A, Evans P, Clow A (2004) The effect of dawn simulation on the cortisol response to awakening in healthy participants. Psychoneuroendocrinology 29, ) Kaida K, Ogawa K, Nittono H, Hayashi M, Takahashi M, Hori T (2006) Self-awakening, sleep inertia, and P3 amplitude in elderly people. Percept Mot Skills 102, ) Hayashi M, Watanabe M, Hori T (1999) The effects of a 20 min nap in the mid-afternoon on mood, performance and EEG activity. Clin Neurophysiol 110, ) Gillberg M, Kecklund G, Axelsson J, Åkerstedt T (1996) The effects of a short daytime nap after restricted night sleep. Sleep 19, ) Tietzel AJ, Lack LC (2001) The short-term benefits of brief and long naps following nocturnal sleep restriction. Sleep 24, ) Brooks A, Lack L (2006) A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? Sleep 29, Industrial Health 2007, 45,

7 A SHORT NAP, BRIGHT LIGHT AND POSITIVE MOOD STATUS ) Campbell SS, Dawson D (1990) Enhancement of nighttime alertness and performance with bright ambient light. Physiol Behav 48, ) Phipps-Nelson J, Redman JR, Dijk DJ, Rajaratnam SM (2003) Daytime exposure to bright light, as compared to dim light, decreases sleepiness and improves psychomotor vigilance performance. Sleep 26, ) Partonen T, Lonnqvist J (2000) Bright light improves vitality and alleviates distress in healthy people. J Affect Disord 57, ) Cajochen C, Zeitzer JM, Czeisler CA, Dijk DJ (2000) Doseresponse relationship for light intensity and ocular and electroencephalographic correlates of human alertness. Behav Brain Res 115, ) Rüger M, Gordijn MC, Beersma DG, de Vries B, Daan S (2006) Time-of-day-dependent effects of bright light exposure on human psychophysiology: comparison of daytime and nighttime exposure. Am J Physiol Regul Integr Comp Physiol 290, R ) Dawson D, Campbell SS (1991) Timed exposure to bright light improves sleep and alertness during simulated night shifts. Sleep 14, ) Campbell SS (1995) Effects of timed bright-light exposure on shift-work adaptation in middle-aged subjects. Sleep 18, ) Badia P, Myers B, Boecker M, Culpepper J, Harsh JR (1991) Bright light effects on body temperature, alertness, EEG and behavior. Physiol Behav 50, ) Hayashi M, Masuda A, Hori T (2003) The alerting effects of caffeine, bright light and face washing after a short daytime nap. Clin Neurophysiol 114, ) Judge TA, Ilies R (2004) Affect and job satisfaction: a study of their relationship at work and at home. J Appl Psychol 89, ) Tamaki M, Shirota A, Hayashi M, Hori T (2000) Restorative effects of a short afternoon nap (<30 min) in the elderly on subjective mood, performance and EEG activity. Sleep Res Online 3, ) Kaida K, Ogawa K, Matsuura N, Takahashi M, Hori T (2006) The relationship between nap habit with self-awakening and generalized self-efficacy. Jpn J Health Psychol 19, 1 9 (in Japanese with English abstract). 25) Milner CE, Fogel SM, Cote KA (2006) Habitual napping moderates motor performance improvements following a short daytime nap. Biol Psychol 73, ) Golden RN, Gaynes BN, Ekstrom RD, Hamer RM, Jacobsen FM, Suppes T, Wisner KL, Nemeroff CB (2005) The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence. Am J Psychiatry 162, ) Hashimoto K, Tokunaga M (1995) Reliability and validity of the Mood Check List (MCL-3) measuring the mood state following exercise. J Health Sci 17, ) Kaida K, Takahashi M, Haratani T, Ostuka Y, Fukasawa K, Nakata A (2006) Indoor exposure to natural bright light prevents afternoon sleepiness. Sleep 29, ) Horne JA, Ostberg O (1976) A self-assessment questionnaire to determine morningness-eveningness in human circadian rhythms. Int J Chronobiol 4, ) Ishihara K, Miyashita A, Inugami M, Fukuda K, Yamazaki K, Miyata Y (1986) The results of investigation by the Japanese version of Morningness-Eveningness Questionnaire. Shinrigaku Kenkyu 57, (in Japanese with English abstract). 31) Radloff LS (1977) The CES-D scale: a self-report depression in scale for research in the general population. Applied Psychological Measurement 1, ) Dinges D, Powell J (1985) Microcomputer analysis of performance on a portable, simple visual RT task during sustained operations. Behav Res Methods Instrum Comput 17, ) Åkerstedt T, Gillberg M (1990) Subjective and objective sleepiness in the active individual. Int J Neurosci 52, ) Stampi C, Stone P, Michimori A (1995) A new quantitative method for assessing sleepiness. Work Stress 9, ) Monk TH (1989) A Visual Analogue Scale technique to measure global vigor and affect. Psychiatry Res 27, ) Kaida K, Takahashi M, Åkerstedt T, Nakata A, Otsuka Y, Haratani T, Fukasawa K (2006) Validation of the Karolinska sleepiness scale against performance and EEG variables. Clin Neurophysiol 117, ) Yokoyama K, Araki S, Kawakami N, Takeshita T (1990) Production of the Japanese edition of profile of mood states (POMS): assessment of reliability and validity. Nippon Koshu Eisei Zasshi 37, (in Japanese with English abstract). 38) Rechtschaffen A, Kales A (1968) A manual of standardized terminology, techniques and scoring system for sleep stage of human subject, National Institute of Health, Washington, DC. 39) Lockley SW, Evans EE, Scheer FA, Brainard GC, Czeisler CA, Aeschbach D (2006) Short-wavelength sensitivity for the direct effects of light on alertness, vigilance, and the waking electroencephalogram in humans. Sleep 29, ) Cajochen C, Munch M, Kobialka S, Krauchi K, Steiner R, Oelhafen P, Orgul S, Wirz-Justice A (2005) High sensitivity of human melatonin, alertness, thermoregulation, and heart rate to short wavelength light. J Clin Endocrinol Metab 90, ) Czeisler CA, Allan JS, Strogatz SH, Ronda JM, Sanchez R, Rios CD, Freitag WO, Richardson GS, Kronauer RE (1986) Bright light resets the human circadian pacemaker independent of the timing of the sleep-wake cycle. Science 233, ) Shanahan TL, Zeitzer JM, Czeisler CA (1997) Resetting the melatonin rhythm with light in humans. J Biol Rhythms 12, ) Burgess HJ, Sharkey KM, Eastman CI (2002) Bright light, dark and melatonin can promote circadian adaptation in night shift workers. Sleep Med Rev 6,

8 308 K KAIDA et al. 44) Hayashi M, Motoyoshi N, Hori T (2005) Recuperative power of a short daytime nap with or without stage 2 sleep. Sleep 28, ) Dinges DF (1995) An overview of sleepiness and accidents. J Sleep Res 4, ) Lal SK, Craig A (2002) Driver fatigue: electroencephalography and psychological assessment. Psychophysiology 39, ) Shen J, Barbera J, Shapiro CM (2006) Distinguishing sleepiness and fatigue: focus on definition and measurement. Sleep Med Rev 10, ) Hayashi M, Hori T (1998) The effects of a 20-min nap before post-lunch dip. Psychiatry Clin Neurosci 52, ) Hayashi M, Ito S, Hori T (1999) The effects of a 20-min nap at noon on sleepiness, performance and EEG activity. Int J Psychophysiol 32, ) Kaida K, Nittono H, Hayashi M, Hori T (2003) Effects of self-awakening on sleep structure of a daytime short nap and on subsequent arousal levels. Percept Mot Skills 97, Industrial Health 2007, 45,