Shigekazu Higuchi

Effects of playing a computer game using a bright display on presleep physiological variables, sleep latency, slow wave sleep and REM sleep

Epidemiological studies have shown that playing a computer game at night delays bedtime and shortens sleeping hours, but the effects on sleep architecture and quality have remained unclear. In the present study, the effects of playing a computer game and using a bright display on nocturnal sleep were examined in a laboratory. Seven male adults (24.7 ± 5.6 years old) played exciting computer games with a bright display (game‐BD) and a dark display (game‐DD) and performed simple tasks with low mental load as a control condition in front of a BD (control‐BD) and DD (control‐DD) between 23:00 and 1:45 hours in randomized order and then went to bed at 2:00 hours and slept until 8:00 hours. Rectal temperature, electroencephalogram (EEG), heart rate and subjective sleepiness were recorded before sleep and a polysomnogram was recorded during sleep. Heart rate was significantly higher after playing games than after the control conditions, and it was also significantly higher after using the BD than after using the DD. Subjective sleepiness and relative theta power of EEG were significantly lower after playing games than after the control conditions. Sleep latency was significantly longer after playing games than after the control conditions. REM sleep was significantly shorter after the playing games than after the control conditions. No significant effects of either computer games or BD were found on slow‐wave sleep. These results suggest that playing an exciting computer game affects sleep latency and REM sleep but that a bright display does not affect sleep variables.

Sleep Debt Elicits Negative Emotional Reaction through Diminished Amygdala-Anterior Cingulate Functional Connectivity

Objectives Sleep debt reportedly increases emotional instability, such as anxiety and confusion, in addition to sleepiness and psychomotor impairment. However, the neural basis of emotional instability due to sleep debt has yet to be elucidated. This study investigated changes in emotional responses that are elicited by the simulation of short-term sleep loss and the brain regions responsible for these changes. Subjects and Methods Fourteen healthy adult men aged 24.1±3.3 years (range, 20–32 years) participated in a within-subject crossover study consisting of 5-day sessions of both sleep debt (4 h for time in bed) and sleep control (8 h for time in bed). On the last day of each session, participants underwent polysomnography and completed the State-Trait Anxiety Inventory and Profile of Mood States questionnaires. In addition, functional magnetic resonance imaging was conducted while performing an emotional face viewing task. Results Restricted sleep over the 5-day period increased the activity of the left amygdala in response to the facial expression of fear, whereas a happy facial expression did not change the activity. Restricted sleep also resulted in a significant decrease in the functional connectivity between the amygdala and the ventral anterior cingulate cortex (vACC) in proportion to the degree of sleep debt (as indicated by the percentage of slow wave sleep and δ wave power). This decrease was significantly correlated with activation of the left amygdala and deterioration of subjective mood state. Conclusion The results of this study suggest that continuous and accumulating sleep debt that can be experienced in everyday life can downregulate the functional suppression of the amygdala by the vACC and consequently enhance the response of the amygdala to negative emotional stimuli. Such functional alteration in emotional control may, in part, be attributed to the neural basis of emotional instability during sleep debt.

Body support effect on standing balance in the visually impaired elderly

OBJECTIVE To evaluate the effectiveness of body support in compensating for decreased standing balance stability in elderly persons with visual impairment. DESIGN Standing balance was measured in a cross-section of elderly persons from two nursing homes--one for aged individuals with visual impairment, the other for aged individuals without visual impairment. PARTICIPANTS The subjects were 44 visually impaired persons with a mean age of 79.0 yrs and 39 people without visual impairment, mean age 76.3 yrs. OUTCOME MEASURES The area of gravity-center sway was measured with subjects standing on a gravicorder for 30sec in three positions: (1) without support, (2) with cane, (3) with light support by touching a wall. RESULTS Both men and women in the visually impaired group swayed more than their sighted counterparts when standing without support, the only statistically significant difference between the two groups. For all subjects, the greatest degree of sway occurred when subjects stood unsupported, and the least sway occurred when subjects touched a wall for support. CONCLUSION In visually impaired elderly persons, touching a wall for body support while standing is more effective than using a cane.

Physical performance tests after stroke: reliability and validity.

ObjectiveTo evaluate the reliability and validity of the modified physical performance tests for stroke survivors who live in a community. DesignThe subjects included 40 stroke survivors and 40 apparently healthy independent elderly persons. The physical performance tests for the stroke survivors comprised two physical capacity evaluation tasks that represented physical abilities necessary to perform the main activities of daily living, e.g., standing-up ability (time needed to stand up from bed rest) and walking ability (time needed to walk 10 m). ResultsRegarding the reliability of tests, significant correlations were confirmed between test and retest of physical performance tests with both short and long intervals in individuals after stroke. Regarding the validity of tests, the authors studied the significant correlations between the maximum isometric strength of the quardriceps muscle and the time needed to walk 10 m, centimeters reached while sitting and reaching, and the time needed to stand up from bed rest. ConclusionsThe authors confirmed that there were significant correlations between the instrumental activity of daily living and the time needed to stand up from bed rest, along with the time needed to walk 10 m for the stroke survivors. These physical performance tests are useful guides for evaluating a level of activity of daily living and physical frailty of stroke survivors living in a community.

Less exposure to daily ambient light in winter increases sensitivity of melatonin to light suppression

This study was carried out to examine the seasonal difference in the magnitude of the suppression of melatonin secretion induced by exposure to light in the late evening. The study was carried out in Akita (39° North, 140° East), in the northern part of Japan, where the duration of sunshine in winter is the shortest. Ten healthy male university students (mean age: 21.9±1.2 yrs) volunteered to participate twice in the study in winter (from January to February) and summer (from June to July) 2004. According to Japanese meteorological data, the duration of sunshine in Akita in the winter (50.5 h/month) is approximately one‐third of that in summer (159.7 h/month). Beginning one week prior to the start of the experiment, the level of daily ambient light to which each subject was exposed was recorded every minute using a small light sensor that was attached to the subjects wrist. In the first experiment, saliva samples were collected every hour over a period of 24 h in a dark experimental room (<15 lux) to determine peak salivary melatonin concentration. The second experiment was conducted after the first experiment to determine the percentage of melatonin suppression induced by exposure to light. The starting time of exposure to light was set 2 h before the time of peak salivary melatonin concentration detected in the first experiment. The subjects were exposed to light (1000 lux) for 2 h using white fluorescent lamps (4200 K). The percentage of suppression of melatonin by light was calculated on the basis of the melatonin concentration determined before the start of exposure to light. The percentage of suppression of melatonin 2 h after the start of exposure to light was significantly greater in winter (66.6±18.4%) than summer (37.2±33.2%), p<0.01). The integrated level of daily ambient light from rising time to bedtime in summer was approximately twice that in winter. The results suggest that the increase in suppression of melatonin by light in winter is caused by less exposure to daily ambient light.

Influence of Light at Night on Melatonin Suppression in Children

CONTEXT The sensitivity of melatonin to light suppression is expected to be higher in children because children have large pupils and pure crystal lenses. However, melatonin suppression by light in children remains unclear. OBJECTIVE We investigated whether light-induced melatonin suppression in children is larger than that in adults. METHODS Thirty-three healthy primary school children (mean age, 9.2 ± 1.5 y) and 29 healthy adults (mean age, 41.6 ± 4.7 y) participated in two experiments. In the first experiment, salivary melatonin concentrations in 13 children and 13 adults were measured at night under a dim light (<30 lux) and a moderately bright light (580 lux) in an experimental facility. Pupil diameters were also measured under dim light and bright light. In the second experiment, melatonin concentrations in 20 children and 16 adults were measured under dim light in the experimental facility and under room light at home (illuminance, 140.0 ± 82.7 lux). RESULTS In experiment 1, the melatonin concentration was significantly decreased by exposure to moderately bright light in both adults and children. Melatonin suppression was significantly larger in children (88.2%; n = 5) than in adults (46.3%; n = 6; P < .01), although the data for some participants were excluded because melatonin concentrations had not yet risen. In experiment 2, melatonin secretion was significantly suppressed by room light at home in children (n = 15; P < .05) but not in adults (n = 11). CONCLUSION We found that the percentage of melatonin suppression by light in children was almost twice that in adults, suggesting that melatonin is more sensitive to light in children than in adults at night.

Validity of the Japanese version of the Munich ChronoType Questionnaire

To assess circadian preference with a score, the Morningness-Eveningness Questionnaire (MEQ) has been used for more than 3 decades now. More recently, the Munich ChronoType Questionnaire (MCTQ) was developed: it asks for sleep-wake behavior on work and free days and uses the midpoint of sleep on free days (MSF), corrected for sleep debt accumulated during the work week as an indicator of chronotype (MSFsc). In this study, we developed a Japanese version of the MCTQ by using a translation/back-translation approach including an examination of its semantic validity. In a subsequent questionnaire survey, 450 adult men and women completed the Japanese versions of the MCTQ and MEQ. Results showed that MEQ scores were significantly negatively correlated with mid-sleep parameters assessed by the MCTQ, on both, work and free days, as well as with the chronotype measure MSFsc (r = −0.580 to −0.652, all p < 0.001). As in the original German version, the strongest correlation was observed between MEQ score and MSF. A physiological validation study using dim light melatonin onset as a circadian phase marker (N = 37) showed a high correlation between chronotype as assessed with the MSFsc (r = 0.542, p < 0.001), and less so for MEQ score (r = −0.402, p = 0.055). These results demonstrate the validity of the Japanese MCTQ and provide further support of the adequacy of the MCTQ as a chronotype measure.

DIURNAL VARIATION IN THE P300 COMPONENT OF HUMAN COGNITIVE EVENT-RELATED POTENTIAL

Diurnal variation in the P300 component of the human cognitive event-related potential (ERP) was examined. The P300 component is considered to be a measure of neuroelectric activity related to cognitive functions such as attention allocation and information processing. Nine diurnally active healthy male subjects whose sleep-wake rhythms were synchronized prior to the experiment were studied. The P300 components oral temperature, heart rate, left- and right-hand grip strength, reaction time, subjectively rated sleepiness, attention level, and fatigue were measured at 08:00, 11:00, 14:00, 17:00, and 20:00. Significant diurnal variations in P300 latency, P300 amplitude, oral temperature, heart rate, left- and right-hand grip strength, subjectively rated sleepiness, and attention level were observed. The P300 latency at 08:00 was significantly longer than at 11:00, 17:00, and 20:00, while the P300 amplitude at 08:00 was significantly greater than at 17:00 and 20:00. The P300 latency was correlated positively with subjectively rated sleepiness and negatively correlated with subjectively rated attention level. These results suggest the existence of diurnal variation in human cognitive functions. (Chronobiology International, 17(5), 669–678, 2000)

Expression profiles of PERIOD1, 2, and 3 in peripheral blood mononuclear cells from older subjects

AIMS Circadian clocks regulate daily rhythms of behavior and physiology such as the sleep-wake cycle and hormonal secretion. Numerous characteristics of the behavioral and physiological processes change with age. In this study, we evaluated the circadian clockwork in older people by measuring daily profiles of PERIOD (PER) gene expression in peripheral blood mononuclear cells (PBMCs). MAIN METHODS Blood samples were collected from 6 healthy older subjects (mean age 62 years) at 2-h intervals over a 24-h period under a semi-constant routine condition where masking effects are minimized. PBMCs were isolated from whole blood and temporal mRNA expression profiles of PER1, PER2, and PER3 were determined by RT-PCR. Phases of the PER rhythms, and times of sleep onset and offset were determined using data from those subjects who showed significant 24-h rhythms. The values for the parameters were compared between the older subjects and 8 young control subjects (mean age 21 years). KEY FINDINGS Prominent daily rhythms of PER1, PER2, and PER3 mRNA levels, advanced sleep-wake timing and advanced phases of PER rhythms were observed in the older subjects compared to the young controls. There was no significant age-related phase difference in PER1 or PER2 rhythm with respect to sleep timing; however, PER3 expression pattern was altered in the older subjects. SIGNIFICANCE This preliminary study shows that human circadian clockwork in PBMCs remains intact at least until the presenile stage and suggests that the altered PER3 expression pattern may reflect decreased homeostatic sleep drive in older people.

Modeling circadian and sleep-homeostatic effects on short-term interval timing

Short-term interval timing i.e., perception and action relating to durations in the seconds range, has been suggested to display time-of-day as well as wake dependent fluctuations due to circadian and sleep-homeostatic changes to the rate at which an underlying pacemaker emits pulses; pertinent human data being relatively sparse and lacking in consistency however, the phenomenon remains elusive and its mechanism poorly understood. To better characterize the putative circadian and sleep-homeostatic effects on interval timing and to assess the ability of a pacemaker-based mechanism to account for the data, we measured timing performance in eighteen young healthy male subjects across two epochs of sustained wakefulness of 38.67 h each, conducted prior to (under entrained conditions) and following (under free-running conditions) a 28 h sleep-wake schedule, using the methods of duration estimation and duration production on target intervals of 10 and 40 s. Our findings of opposing oscillatory time courses across both epochs of sustained wakefulness that combine with increasing and, respectively, decreasing, saturating exponential change for the tasks of estimation and production are consistent with the hypothesis that a pacemaker emitting pulses at a rate controlled by the circadian oscillator and increasing with time awake determines human short-term interval timing; the duration-specificity of this pattern is interpreted as reflecting challenges to maintaining stable attention to the task that progressively increase with stimulus magnitude and thereby moderate the effects of pacemaker-rate changes on overt behavior.