Effects of fearful face presentation time and observer's eye movement on the gaze cue effect.

BACKGROUND: There are many conflicting findings on the gaze cueing effect (GCE) of emotional facial expressions. This study aimed to investigate whether an averted gaze, accompanied by a fearful expression of different durations, could enhance attentional orientation, as measured by a participant's eye movements. METHODS: Twelve participants (3 females) completed the gaze cue task, reacting to a target location after observing changes in the gaze and expression of a face illustrated on a computer screen. Meanwhile, participants' eye movements were monitored by electrooculography. The GCE was calculated by reaction time as an indicator of attention shift. RESULTS: The analysis of the overall data did not find a significant effect of fearful facial expressions on the GCE. However, analysis of trial data that excluded a participant's eye movement data showed that brief (0, 100 ms) presentation of the fearful facial expression enhanced the GCE compared to that during a neutral facial expression, although when the presentation time of the fearful expression was increased to 200 or 400 ms, the GCE of the fearful expression was at the same level as when model showed a neutral expression. CONCLUSIONS: The results suggest that the attention-enhancing effect of gaze cues induced by rapidly presented fearful expressions occurs only when the effect of eye movement trials is excluded. This effect may be mediated by reflexively neural circuits in the amygdala that process threatening stimuli. However, as the expression duration increased, the fearful expression's attention-enhancing effect decreased. We suggest that future studies on the emotion modulation of GCE should consider the negative effects of participants' saccades and blinks on the experimental results.

Heart rate and heart rate variability in infants during olfactory stimulation.

Background: Various plant odours have been shown to decrease heart rate and increase parasympathetic nervous activity. However, 'innate' autonomic responses without the influences of experience, assumptions and prejudices of odours remains unclear. Aim: To clarify changes in heart rate and heart rate variability in infants while presenting different components of plant odours. Subjects and methods: The study participants included 17 infants aged 1-3.5 months. Each infant was exposed to the odours of α-pinene, D-limonene and air (as a control) for 2 minutes after a 2-minute resting period without any odours. The intervals of heartbeat (R-R intervals) were recorded during this process. Results: Heart rate significantly decreased in response to the odour of limonene. Frequency analysis of heart rate variability revealed that the power value at 0.2 Hz was significantly higher during the odour presentation of limonene compared to the baseline and that at 0.1 Hz and 0.4 Hz was significantly lower during α-pinene presentation. Conclusion: Autonomic responses to specific natural odours may be partly shaped innately, while underlying physiological mechanisms may be different between infants and adults.

Revisiting human cerebral blood flow responses to augmented blood pressure oscillations.

KEY POINTS: Cerebral autoregulation is most effective in buffering against pressure fluctuations slower than 0.03 Hz (∼30 s). This suggests that frequency bands for characterizing cerebral autoregulation should be redefined Low cross-spectral coherence below 0.03 Hz highlights the limitations of transfer function approaches Haemodynamic changes induced by lower body pressure could not fully explain the differences in autoregulation estimated from spontaneous vs. augmented fluctuations, and thus, observations of spontaneous fluctuations should not be relied on whenever possible. ABSTRACT: There is currently little empirical basis for time scales that are considered to be most significant in cerebrovascular counter-regulation of changes in arterial pressure. Although it is well established that cerebral autoregulation behaves as a 'high-pass' filter, recommended frequency bands have been largely arbitrarily determined. To test effectiveness of cerebral autoregulation, we refined oscillatory lower body pressure (LBP) to augment resting pressure fluctuations below 0.1 Hz by a factor of two in 13 young male volunteers, and thoroughly characterized the time and frequency responses of cerebral autoregulation. We observed that despite a threefold increase in arterial pressure power <0.03 Hz with oscillatory LBP, there was no change in cerebral blood flow power, indicating near perfect counter-regulation. By contrast, in the range 0.03-0.10 Hz, both cerebral blood flow and arterial pressure power more than doubled. Our data demonstrate that cerebral autoregulation is most effective in buffering against pressure fluctuations slower than 0.03 Hz (∼30 s). This suggests that frequency bands of interest should be redefined and recording length should be increased considerably to account for this. Furthermore, low cross-spectral coherence below 0.03 Hz, even when pressure fluctuations were augmented, highlights the uncertainty in transfer function approaches and the need to either report precision or use non-linear approaches. Finally, haemodynamic changes induced by LBP could not fully explain the differences in autoregulation estimated from spontaneous vs. augmented fluctuations, and thus, observations of spontaneous fluctuations should not be relied on whenever possible.

Relative contributions of systemic hemodynamic variables to cerebral autoregulation during orthostatic stress.

Postural changes impair the ability of the cerebrovasculature to buffer against dynamic pressure fluctuations, but the mechanisms underlying this impairment have not been elucidated. We hypothesized that autoregulatory impairment may reflect the impact of static central volume shifts on hemodynamic factors other than arterial pressure (AP). In 14 young volunteers, we assessed the relation of fluctuations in cerebral blood flow (CBF) to those in AP, cardiac output, and CO2, during oscillatory lower body pressure (LBP) (±20 mmHg at 0.01 and 0.06 Hz) at three static levels (-20, 0, and +20 mmHg). Static and dynamic changes in AP, cardiac output, and CO2 explained over 70% of the variation in CBF fluctuations. However, their contributions were different across frequencies and levels: dynamic AP changes explained a substantial proportion of the variation in faster CBF fluctuations (partial R2 = 0.75, standardized ß = 0.83, P < 0.01), whereas those in CO2 explained the largest portion of the variation in slow fluctuations (partial R2 = 0.43, ß = 0.51, P < 0.01). There was, however, a major contribution of slow dynamic AP changes during negative (ß = 0.43) but not neutral (ß = 0.05) or positive (ß = -0.07) LBP. This highlights the differences in contributions of systemic variables to dynamic and static autoregulation and has important implications for understanding orthostatic intolerance. NEW & NOTEWORTHY While fluctuations in blood pressure drive faster fluctuations in cerebral blood flow, overall level of CO2 and the magnitude of its fluctuations, along with cardiac output, determine the magnitude of slow ones. The effect of slow blood pressure fluctuations on cerebrovascular responses becomes apparent only during pronounced central volume shifts (such as when standing). This underlines distinct but interacting contributions of static and dynamic changes in systemic hemodynamic variables to the cerebrovascular regulation.

Cathodal transcranial direct-current stimulation over right posterior parietal cortex enhances human temporal discrimination ability.

BACKGROUND: Time perception associated with durations from 1 s to several minutes involves activity in the right posterior parietal cortex (rPPC). It is unclear whether altering the activity of the rPPC affects an individual's timing performance. Here, we investigated the human timing performance under the application of transcranial direct-current stimulation (tDCS) that altered the neural activities of the rPPC. METHODS: We measured the participants' duration-discrimination threshold by administering a behavioral task during the tDCS application. The tDCS conditions consisted of anodal, cathodal, and sham conditions. The electrodes were placed over the P4 position (10-20 system) and on the left supraorbital forehead. On each task trial, the participant observed two visual stimuli and indicated which was longer. The amount of difference between the two stimulus durations was varied repeatedly throughout the trials according to the participant's responses. The correct answer rate of the trials was calculated for each amount of difference, and the minimum amount with the correct answer rate exceeding 75% was selected as the threshold. The data were analyzed by a linear mixed-effects models procedure. RESULTS: Nineteen volunteers participated in the experiment. We excluded three participants from the analysis: two who reported extreme sleepiness while performing the task and one who could recognize the sham condition correctly with confidence. Our analysis of the 16 participants' data showed that the average value of the thresholds observed under the cathodal condition was lower than that of the sham condition. This suggests that inhibition of the rPPC leads to an improvement in temporal discrimination performance, resulting in improved timing performance. CONCLUSIONS: In the present study, we found a new effect that cathodal tDCS over the rPPC enhances temporal discrimination performance. In terms of the existence of anodal/cathodal tDCS effects on human timing performance, the results were consistent with a previous study that investigated temporal reproduction performance during tDCS application. However, the results of the current study further indicated that cathodal tDCS over the rPPC increases accuracy of observed time duration rather than inducing an overestimation as a previous study reported.

Additive Effects of Sinusoidal Lower Body Negative Pressure on Cardiovascular Responses.

BACKGROUND: Sinusoidal lower body negative pressure (SLBNP) has been used to investigate the cardiovascular response to slow periodic changes in blood shifts, but measurements of slow fluctuations take a long time if measured for each period of SLBNP separately. Our study aimed to investigate whether the cardiovascular responses to superimposed SLBNP (S-SLBNP), which is expected to reduce the measurement time, are different from responses measured individually. METHODS: S-SLBNP was configured by superimposing two conventional SLBNPs (C-SLBNP) at 180-s and 30-s periods in the pressure range from 0 to -25 mmHg. As the S-SLBNP has double the static load of C-SLBNP, we also used offset SLBNP (O-SLBNP), which has the same static load level as S-SLBNP. Heart rate (HR), thoracic impedance (Z0), and mean arterial pressure (MAP) were measured from 11 male subjects. The transfer functions of gains from MAP to HR (Gain-HR/MAP) and from Z0 to HR (Gain-HR/Z0) were calculated as indexes of arterial baroreflex and cardiopulmonary baroreflex regulation of HR, respectively. RESULTS: The Gain-HR/MAP in the 180-s period (2.11 ± 0.17 bpm/mmHg; mean ± SEM) was larger than that of the 30-s period (1.04 ± 0.09 bpm/mmHg); however, there was no significant difference between the SLBNP conditions. The Gain-HR/Z0 in C-SLBNP (9.37 ± 1.47 bpm/ohm) was smaller than that of the other conditions [18.46 ± 2.45 bpm/ohm (O-SLBNP); 16.09 ± 2.29 bpm/ohm (S-SLBNP)]. DISCUSSION: Using S-SLBNP could reduce the measurement time needed to examine the arterial baroreflex. However, the cardiopulmonary baroreflex was modified by the static load of SLBNP.Ishibashi K, Oyama F, Yoshida H, Iwanaga K. Additive effects of sinusoidal lower body negative pressure on cardiovascular responses. Aerosp Med Hum Perform. 2017; 88(2):137-141.

Beneficial effects of vildagliptin combined with miglitol on glucose tolerance and islet morphology in diet-controlled db/db mice.

Dipeptidyl peptidase-4 (DPP-4) inhibitors improve glycemic control in patients with type 2 diabetes primarily by increasing plasma active glucagon-like peptide-1 (GLP-1) levels. While various combination therapies based on DPP-4 inhibitors have been proposed for treatment of type 2 diabetes, the effects of combination therapy of DPP-4 inhibitors and alpha-glucosidase inhibitors on ß-cell function are less characterized. We evaluated the effects of long-term treatment with vildagliptin, a DPP-4 inhibitor, on metabolic parameters and ß-cell function, in combination with miglitol, an alpha-glucosidase inhibitor, in diet-controlled db/db mice. In this study, 6-week-old male db/db mice were provided with standard chow twice a day for 6 weeks. Meal tolerance tests and glucose tolerance tests showed that the combination therapy of vildagliptin with miglitol, but not each alone, suppressed postprandial glycemic excursion, enhanced postprandial active GLP-1 levels and prevented deterioration of glucose tolerance in the db/db mice. The combination treatment did not alter ß-cell mass, but resulted in preserved expression of glucose transporter 2, Zinc transporter 8 and MafA and reduced the number of α cells. These results suggest that the combination of vildagliptin and miglitol prevents the development of overt diabetes in diet-controlled pre-diabetic db/db mice by normalizing postprandial glucose and incretin response, and by preserving ß-cell structure and the expression of factors essential for ß-cell function.

Comparison of cardiovascular response to sinusoidal and constant lower body negative pressure with reference to very mild whole-body heating.

BACKGROUND: The purpose of the present study was to compare sinusoidal versus constant lower body negative pressure (LBNP) with reference to very mild whole-body heating. Sinusoidal LBNP has a periodic load component (PLC) and a constant load component (CLC) of orthostatic stress, whereas constant LBNP has only a CLC. We tested two sinusoidal patterns (30-s and 180-s periods with 25 mmHg amplitude) of LBNP and a constant LBNP with -25 mmHg in 12 adult male subjects. RESULTS: Although the CLC of all three LBNP conditions were configured with -25 mmHg, the mean arterial pressure (MAP) results showed a significantly large decrease from baseline in the 30-s period condition (P <0.01). In contrast, the other cardiovascular indices (heart rate (HR), stroke volume (SV), cardiac output (CO), basal thoracic impedance (Z(0)), total peripheral resistance (TPR), the natural logarithmic of the HF component (lnHF), and LF/HF (ln(LF/HF))) of heart rate variability (HRV) showed relatively small variations from baseline in the 30-s period condition (P <0.01). The result of the gain and phase of transfer function at the sinusoidal period of LBNP showed that the very mild whole-body heating augmented the orthostatic responses. CONCLUSION: These results revealed that the effect of the CLC of LBNP on cardiovascular adjustability was attenuated by the addition of the PLC to LBNP. Based on the results of suppressed HRV response from baseline in the 30-s period condition, we suggest that the attenuation may be caused by the suppression of the vagal responsiveness to LBNP.

Thermoregulatory effect in humans of suppressed endogenous melatonin by pre-sleep bright-light exposure in a cold environment.

This study investigated the physiological function of suppressed melatonin through thermoregulation in a cold environment. Interactions between thermoregulation directly affected by exposure to a cold environment and indirectly affected by endogenous melatonin suppression by bright-light exposure were examined. Ten male subjects were exposed to two different illumination intensities (30 and 5000 lux) for 4.5 h, and two different ambient temperatures (15 and 27 degrees C) for 2 h before sleep under dark and thermoneutral conditions. Salivary melatonin level was suppressed by bright light (p < 0.001), although the ambient temperature condition had no significant effect on melatonin. During sleep, significant effects of pre-sleep exposure to a cold ambient temperature (p < 0.001) and bright light (p < 0.01) on rectal temperature (T(re)) were observed. Pre-sleep, bright-light exposure led to an attenuated fall in T(re) during sleep. Moreover, T(re) dropped more precipitously after cold exposure than thermoneutral conditions (cold: -0.54 +/- 0.07 degrees C/h; thermoneutral: -0.16 +/- 0.03 degrees C/h; p < 0.001). Pre-sleep, bright-light exposure delayed the nadir time of T(re) under thermoneutral conditions (p < 0.05), while cold exposure masked the circadian rhythm with a precipitous decrease in T(re). A significant correlation between the T(re) nadir and melatonin level (r = -0.774, p < 0.05) indicated that inter-individual differences with higher melatonin levels lead to a reduction in T(re) after cold exposure. These results suggest that suppressed endogenous melatonin inhibits the downregulation of the body temperature set-point during sleep.

Essential oil of lavender inhibited the decreased attention during a long-term task in humans.

This study examined the effects of odors on sustained attention during a vigilance task. Two essential oils (lavender and eucalyptus) and two materials (l-menthol and linalyl acetate) were compared with a control. The increase in reaction time was significantly lower with lavender than with the control. The results suggest that the administration of lavender helped to maintain sustained attention during the long-term task.

Inter-individual difference in pupil size correlates to suppression of melatonin by exposure to light.

There are large inter-individual differences in pupil size and suppression of melatonin by exposure to light. It has been reported that melatonin suppression by exposure to light increases when pupils are pharmacologically dilated. However, the correlation between normal inter-individual difference in pupil size and melatonin suppression by exposure to light is not clear. Twenty-three healthy male subjects (22.6+/-2.7 years old) were exposed to light (1000 lx) for 2 h at night. The starting time of exposure to light was set to the ascending phase of melatonin concentration of each subject. Pupil area and saliva melatonin concentration were measured before exposure to light under dim light (15 lx) and during exposure to light. There were large inter-individual differences in melatonin suppression and pupil area. The mean and standard deviation of percentage of melatonin suppression 2 h after exposure to light was 57.2+/-22.1%. The mean and standard deviation of pupil areas before and 2 h after exposure to light were 30.7+/-7.9 mm2 and 15.9+/-4.8 mm2, respectively. The percentage of melatonin suppression by light was positively correlated with pupil area during light exposure (r=0.525, p<0.02). Interestingly, it was also correlated with pupil area measured before exposure to light, under dim light (15 lx) (r=0.658, p<0.001). These results suggest that inter-individual difference in pupil area positively correlates with melatonin suppression by light and that pupil area under dim light is a predictor of inter-individual differences in melatonin suppression by light.

Involvement of basal metabolic rate in determination of type of cold tolerance.

This study aimed to assess the relationship between basal metabolic rate (BMR) and metabolic heat production, and to clarify the involvement of BMR in determining the phenotype of cold tolerance. Measurements of BMR, maximum oxygen uptake, and cold exposure test were conducted on ten males. In the cold exposure test, rectal (T(rec)) and mean skin temperatures (T(ms)), oxygen uptake, and blood flow at forearm (BF(arm)) were measured during exposure to cold (10 degrees C) for 90 min. Significant correlations were observed between BMR and increasing rate of oxygen uptake, as well as between decreasing rate of BF(arm) and increasing rate of oxygen uptake at the end of cold exposure. These findings suggested that individuals with a lower BMR were required to increase their metabolic heat production during cold exposure, and that those with a higher BMR were able to moderate increased metabolic heat production during cold exposure because they were able to reduce heat loss. This study showed that BMR is an important factor in determining the phenotype of cold tolerance, and that individuals with a low BMR showed calorigenic-type cold adaptation, whereas subjects with a high BMR exhibited adiabatic-type cold adaptation by peripheral vasoconstriction.

Influence of eye colors of Caucasians and Asians on suppression of melatonin secretion by light.

This experiment tested effects of human eye pigmentation depending on the ethnicity on suppression of nocturnal melatonin secretion by light. Ten healthy Caucasian males with blue, green, or light brown irises (light-eyed Caucasians) and 11 Asian males with dark brown irises (dark-eyed Asians) volunteered to participate in the study. The mean ages of the light-eyed Caucasians and dark-eyed Asians were 26.4 +/- 3.2 and 25.3 +/- 5.7 years, respectively. The subjects were exposed to light (1,000 lux) for 2 h at night. The starting time of exposure was set to 2 h before the time of peak salivary melatonin concentration of each subject, which was determined in a preliminary experiment. Salivary melatonin concentration and pupil size were measured before exposure to light and during exposure to light. The percentage of suppression of melatonin secretion by light was calculated. The percentage of suppression of melatonin secretion 2 h after the start of light exposure was significantly larger in light-eyed Caucasians (88.9 +/- 4.2%) than in dark-eyed Asians (73.4 +/- 20.0%) (P < 0.01). No significant difference was found between pupil sizes in light-eyed Caucasians and dark-eyed Asians. These results suggest that sensitivity of melatonin to light suppression is influenced by eye pigmentation and/or ethnicity.

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 degrees North, 140 degrees 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 subject's 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.

Inhibition of heart rate variability during sleep in humans by 6700 K pre-sleep light exposure.

Two different spectral analyses of heart rate (HR) variability (HRV) were performed on seven young male subjects to evaluate the effects of different color temperatures of light exposure (6700 K, 5000 K, 3000 K) before sleep on cardiac vagal activity. In investigating HRV, we used an ordinary fast Fourier transform (FFT) and coarse graining spectral analysis (CGSA), which selectively extracts random fractal components from a given time series. The results showed that suppressions of HR during sleep after 6700 K light exposure were more inhibited than the other two lighting conditions. Increases in high-frequency (HF) components of HRV during sleep were also inhibited by 6700 K pre-sleep lighting. These results indicate that pre-sleep exposure to light of a higher color temperature may inhibit the enhancement of cardiac vagal activity during sleep. Moreover, significant HF alterations were shown in fractal-free HF (not in ordinary HF) components by CGSA. Because the HF component originates from respiratory sinus arrhythmia with periodical fluctuations, CGSA may be an appropriate approach for HRV evaluation during sleep.

Error and individual difference in cardiovascular responses to orthostatic stress in humans.

Variations in cardiovascular responses to orthostatic stress were investigated in terms of physiological polymorphism. Variations of physiological measurements are subdivided into individual differences and measurement errors. However, individual differences are often considered to be an error in statistical analysis due to its limitations in experimental design. In order to discuss about the relative contribution of individual difference in cardiovascular responses to postural changes, percent contribution (PC) was estimated using the Taguchi method. Six healthy male adults (age range: 21-27) were subjected to orthostatic stress by inducing a postural inclination of 60 degrees head-up-tilting to the horizontal, and the responses were measured thrice in each subject on different days. The respective changes of heart rate (HR) and stroke volume (SV) in the period from the resting supine to the head-up-tilt position were significantly increased (p < 0.01) and decreased (p < 0.01) without affecting the mean blood pressure (MBP). The PC of individual difference in HR showed a significantly higher ratio of individual difference during the head-up-tilt (71.4-76.2%) compared with supine rest (0.0-50.4%). While the main variations of HR during supine rest were not the individual differences between the subjects, the day-to-day differences within the subject were significant. The PC of individual differences in MBP and SV constantly displayed a significant difference between the subjects. These results suggest that the strategy for maintaining stable cardiovascular regulation may be different even in normal subjects. In the perspective of physiological parameters, PC monitoring may serve as an empirical approach to evaluate physiological polymorphism.

Relationship between individual difference in melatonin suppression by light and habitual bedtime.

The purpose of this study was to determine the relationship between individual difference in melatonin suppression by exposure to light and habitual bedtime. Seventeen healthy male students (mean age: 22.6+/-2.4 yr) volunteered to participate in the study. The subjects were exposed to light (1000 lx) for 2 hours from 2 hours before the time of peak salivary melatonin concentration. Two hours after exposure to the light, melatonin suppression had occurred in fifteen subjects. No significant correlation was found between the rate of melatonin suppression and habitual bedtime in the fifteen subjects in whom melatonin suppression occurred. However, the habitual bedtime of the two subjects in whom melatonin suppression did not occur was earlier than that of the other subjects. These results suggest that there are some people with very low sensitivity to light and that this may affect habitual bedtime.

Effects of lifestyle, body composition, and physical fitness on cold tolerance in humans.

In the present study, we attempted to clarify the effects of lifestyle and body compositions on basal metabolism and to clarify the effects of physical training on thermoregulatory responses to cold. Basal metabolism, body compositions, and questionnaires regarding lifestyle were evaluated in 37 students. From multiple linear regression analysis, sex, muscle weight, fat intake, and diurnal temperature were selected as significant explanatory variables. In a second experiment, rectal and the skin temperature at 7 different points as well as the oxygen uptake of eight males were measured at 10 degrees C for 90 min before and after training. The decline in rectal temperature that was observed before training was not observed after training. In addition, rectal temperature was significantly higher at post-training than at pre-training. These results suggest that some lifestyle factors affect cold tolerance; in particular, daily activity might improve our ability to control heat radiation and basal heat production.

Effect of color temperature of light sources on slow-wave sleep.

In order to examine whether the spectral compositions of light source may affect sleep quality, sleep architecture under different color temperatures of light sources was evaluated. Seven healthy males were exposed to the light sources of different color temperatures (3000 K, 5000 K and 6700 K) for 6.5 h before sleep. The horizontal illuminance level was kept at 1000 lux. Subjects slept on a bed in near darkness (< 10 lux) after extinguishing the light, and polysomnograms recorded the sleep parameters. In the early phase of the sleep period, the amount of stage-4 sleep (S4-sleep) was significantly attenuated under the higher color temperature of 6700 K compared with the lower color temperature of 3000 K. Present findings suggest that light sources with higher color temperatures may affect sleep quality in a view that S4-sleep period is important for sleep quality.

Non-visual effects of the color temperature of fluorescent lamps on physiological aspects in humans.

The non-visual effects of the color temperature of fluorescent lamps were reviewed based mainly on our recent studies with special reference to physiological aspects in humans such as arousal level, autonomic nerve system including heart rate variability, blood pressure and body temperature regulation, and sleep architecture. It was concluded that there obviously existed the non-visual effects of the spectral composition of fluorescent lamps on physiological aspects, as predicted based on the functions of the nuclei located on the photic non-visual pathway.