Body temperature and mood variations during forced desynchronization in winter depression: a preliminary report

Seasonal Forest Changes of Color and Temperature: Effects on the Mood and Physiological State of University Students

In this study, we attempted to analyze the effect of color and temperature changes in the forest environment over time on the mood and physiological state of university students. The survey was conducted four times considering forest changes such as new leaf appearance and growth, autumn leaf changes, and fallen leaves. The participants' moods and physiological states were first evaluated in an indoor environment; a second evaluation was conducted after contact with the forest. The color visual information of the forest environment was analyzed through color extraction from photographs taken each survey day. The participants' moods and physiological states were measured using the Korean Profile of Mood States-Brief and a heart rate variability measuring device, respectively. Changes in the forest experience according to the season had an effect on university students' mood states. In particular, the effects of the spring forest experience included the relaxation of tension and the activation of vigor. This result is considered to be influenced by factors such as the season's temperature and the green color, which is predominant in the spring forest. However, no physiological changes were found in the participants according to each season. The results of this study can lead to greater consideration of the role of color in urban forest planning for universities and other public spaces.

Bright Light Increases Alertness and Not Cortisol in Healthy Men: A Forced Desynchrony Study Under Dim and Bright Light (I)

Light-induced improvements in alertness are more prominent during nighttime than during the day, suggesting that alerting effects of light may depend on internal clock time or wake duration. Relative contributions of both factors can be quantified using a forced desynchrony (FD) designs. FD designs have only been conducted under dim light conditions (<10 lux) since light above this amount can induce non-uniform phase progression of the circadian pacemaker (also called relative coordination). This complicates the mathematical separation of circadian clock phase from homeostatic sleep pressure effects. Here we investigate alerting effects of light in a novel 4 × 18 h FD protocol (5 h sleep, 13 h wake) under dim (6 lux) and bright light (1300 lux) conditions. Hourly saliva samples (melatonin and cortisol assessment) and 2-hourly test sessions were used to assess effects of bright light on subjective and objective alertness (electroencephalography and performance). Results reveal (1) stable free-running cortisol rhythms with uniform phase progression under both light conditions, suggesting that FD designs can be conducted under bright light conditions (1300 lux), (2) subjective alerting effects of light depend on elapsed time awake but not circadian clock phase, while (3) light consistently improves objective alertness independent of time awake or circadian clock phase. Reconstructing the daily time course by combining circadian clock phase and wake duration effects indicates that performance is improved during daytime, while subjective alertness remains unchanged. This suggests that high-intensity indoor lighting during the regular day might be beneficial for mental performance, even though this may not be perceived as such.

Living Without Temporal Cues: A Case Study

Isolation from external time cues allows endogenous circadian rhythmicity to be demonstrated. In this study, also filmed as a television documentary, we assessed rhythmic changes in a healthy man time isolated in a bunker for 9 days/nights. During this period the lighting conditions were varied between: (1) self-selected light/dark cycle, (2) constant dim light, and (3) light/dark cycle with early wake up. A range of variables was assessed and related to the sleep-wake cycle, psychomotor and physical performance and clock-time estimation. This case study using modern non-invasive monitoring techniques emphasizes how different physiological circadian rhythms persist in temporal isolation under constant dim light conditions with different waveforms, free-running with a period (τ) between 24 and 25 h. In addition, a significant correlation between time estimation and mid-sleep time, a proxy for circadian phase, was demonstrated.

Diurnal mood variation in depression: a signal of disturbed circadian function?

BACKGROUND

Diurnal variation in mood is a prominent symptom of depression, and is typically experienced as positive mood variation (PMV - mood being worse upon waking and better in the evening). The present study sought to advance understanding of PMV by measuring daily mood variation in non-clinical individuals with varying levels of depressed mood. Based on research into normative variation in mood and evidence that circadian amplitudes may be decreased in depression, it was hypothesised that compared to those with low levels of depression, individuals meeting Centre for Epidemiological Studies-Depression Scale (CES-D) cut-off for probable depression would exhibit an attenuated circadian component in diurnal variation of Positive Affect (PA).

METHOD

Ninety-nine young healthy women (mean age=21.5, SD=3.0) living on a normal sleep-wake schedule provided mood reports every two hours between 0800 h and 2200 h for 7 days.

RESULTS

The high depression group (CES-D > or = 23, n=22) exhibited a pattern of diurnal variation consistent with PMV (increased PA in the evening relative to the morning). As predicted, evidence was also found that the high depression group was characterized by a decreased circadian component to diurnal variation in PA relative to the low depression group (CES-D < 23, n=77).

CONCLUSIONS

It is provisionally concluded that diurnal mood variation in depression can usefully be understood from the perspective of weakened circadian function. Findings are discussed in terms of limitations of the study's naturalistic design and future research avenues identified.

BOLD fMRI deactivation of limbic and temporal brain structures and mood enhancing effect by transcutaneous vagus nerve stimulation

Direct vagus nerve stimulation (VNS) has proved to be an effective treatment for seizure disorder and major depression. However, since this invasive technique implies surgery, with its side-effects and relatively high financial costs, a non-invasive method to stimulate vagal afferences would be a great step forward. We studied effects of non-invasive electrical stimulation of the nerves in the left outer auditory canal in healthy subjects (n = 22), aiming to activate vagal afferences transcutaneously (t-VNS). Short-term changes in brain activation and subjective well-being induced by t-VNS were investigated by functional magnetic resonance imaging (fMRI) and psychometric assessment using the Adjective Mood Scale (AMS), a self-rating scale for current subjective feeling. Stimulation of the ear lobe served as a sham control. fMRI showed that robust t-VNS induced BOLD-signal decreases in limbic brain areas, including the amygdala, hippocampus, parahippocampal gyrus and the middle and superior temporal gyrus. Increased activation was seen in the insula, precentral gyrus and the thalamus. Psychometric assessment revealed significant improvement of well-being after t-VNS. Ear lobe stimulation as a sham control intervention did not show similar effects in either fMRI or psychometric assessment. No significant effects on heart rate, blood pressure or peripheral microcirculation could be detected during the stimulation procedure.

CONCLUSIONS

Our study shows the feasibility and beneficial effects of transcutaneous nerve stimulation in the left auditory canal of healthy subjects. Brain activation patterns clearly share features with changes observed during invasive vagus nerve stimulation.

Circadian phase shifting, alerting, and antidepressant effects of bright light treatment

Bright light treatment is the most potent melatonin suppressor and circadian phase shifter and is a safe nonpharmacologic antidepressant for seasonal depression. In addition, bright light treatment may restore performance in conditions of sleep debt and misalignment between peak performance and the athletic event. This article discusses the therapeutic use of bright light treatment, its side effects, and mechanisms of action.

Spontaneous internal desynchronization of locomotor activity and body temperature rhythms from plasma melatonin rhythm in rats exposed to constant dim light

Background

We have recently reported that spontaneous internal desynchronization between the locomotor activity rhythm and the melatonin rhythm may occur in rats (30% of tested animals) when they are maintained in constant dim red light (LL_dim) for 60 days. Previous work has also shown that melatonin plays an important role in the modulation of the circadian rhythms of running wheel activity (R_w) and body temperature (T_b). The aim of the present study was to investigate the effect that desynchronization of the melatonin rhythm may have on the coupling and expression of circadian rhythms in R_w and T_b.

Methods

Rats were maintained in a temperature controlled (23–24°C) ventilated lightproof room under LL_dim (red dim light 1 μW/cm² [5 Lux], lower wavelength cutoff at 640 nm). Animals were individually housed in cages equipped with a running wheel and a magnetic sensor system to detect wheel rotation; T_b was monitored by telemetry. T_b and R_w data were recorded in 5-min bins and saved on disk. For each animal, we determined the mesor and the amplitude of the R_w and T_b rhythm using waveform analysis on 7-day segments of the data. After sixty days of LL_dim exposure, blood samples (80–100 μM) were collected every 4 hours over a 24-hrs period from the tail artery, and serum melatonin levels were measured by radioimmunoassay.

Results

Twenty-one animals showed clear circadian rhythms R_w and T_b, whereas one animal was arrhythmic. R_w and T_b rhythms were always strictly associated and we did not observe desynchronization between these two rhythms. Plasma melatonin levels showed marked variations among individuals in the peak levels and in the night-to-day ratio. In six rats, the night-to-day ratio was less than 2, whereas in the rat that showed arrhythmicity in R_w and T_b melatonin levels were high and rhythmic with a large night-to-day ratio. In seven animals, serum melatonin levels peaked during the subjective day (from CT0 to CT8), thus suggesting that in these animals the circadian rhythm of serum melatonin desynchronized from the circadian rhythms of R_w and T_b. No significant correlation was observed between the amplitude (or the levels) of the melatonin profile and the amplitude and mesor of the R_w and T_b rhythms.

Conclusion

Our data indicate that the free-running periods (τ) and the amplitude of R_w and T_b were not different between desynchronized and non-desynchronized rats, thus suggesting that the circadian rhythm of serum melatonin plays a marginal role in the regulation of the R_w and T_b rhythms. The present study also supports the notion that in the rat the circadian rhythms of locomotor activity and body temperature are controlled by a single circadian pacemaker.

Effect of long-term exposure to constant dim light on the circadian system of rats

The newly discovered multi-oscillatory nature of the mammalian circadian clock system and the cloning of the genes involved in the molecular mechanism that generates circadian rhythmicity have opened new approaches for understanding how mammals are temporally organized and how the mammalian circadian system reacts to the lack of normal synchronization cues. In the present study we investigated the effects of long-term exposure to constant red dim light on the pattern of the expression of Period 1 in the suprachiasmatic nuclei of the hypothalamus and of Arylalkylamine N-acetyltransferase(Aa-nat) in the retina and pineal gland. Our data demonstrate that Period 1 mRNA expression in the suprachiasmatic nuclei of the hypothalamus was not affected by exposure to constant red dim light for 60 days, whereas Aa-nat mRNA expression in the retina and in the pineal gland was significantly affected, since in some animals (20-30%) Aa-nat mRNA levels were found to be higher during the subjective day. A circadian rhythm of serum melatonin and locomotor activity was present in all the animals tested. In 4 animals serum melatonin levels were high during the subjective day. Our data suggest that long-term exposure to constant red dim light may induce desynchronization between the circadian rhythm of locomotor activity and serum melatonin levels.

Update on the biology of seasonal affective disorder

The etiology and pathophysiology of seasonal affective disorder (SAD) has been linked to the seasons and to light since its first conceptualization. Aspects of SAD that make it particularly amenable to biological investigation include the predictable recurrent episodes, the rapid response to a nonpharmacologic treatment, the specific neurovegetative features, and the availability of rich animal models of seasonality. This paper reviews new findings for the major biological hypotheses for SAD, focusing on circadian rhythms, neurotransmitters, and molecular genetics. Integrative issues and future directions for the study of SAD, including the heuristic value of a dual-vulnerability hypothesis that conceptualizes seasonality as a dimensional construct and the importance of studying endophenotypes, will be discussed.

Pharmacological modulation of circadian rhythms: a new drug target in psychotherapeutics

Daily variation in an organism's physiology and behaviour is regulated by the synchrony that is achieved between the internal timing mechanisms - the circadian rhythms of the biological clock - and the prevailing environmental cues. Proper synchrony constitutes an adaptive response; improper or lost synchrony may well yield maladaptation and, in the case of humans, a psychiatric disorder. On a basic level, the circadian system is comprised of three parts: a central oscillator, its various neuronal inputs and its outputs. For all three of these parts, the dissemination of new information is moving at an unprecedented pace, and the number of molecular targets for the opportunistic pharmacologist is growing in step. Monoamines, neuropeptides, kinases - sorting through all these, much less developing one into a drug discovery programme, may be the biggest challenge. However, the potential benefits in targeting a basic flaw in a fundamental biological system may be enormous.

A forced desynchrony study of circadian pacemaker characteristics in seasonal affective disorder

The circadian pacemaker is an endogenous clock that regulates oscillations in most physiological and psychological processes with a near 24-h period. In many species, this pacemaker triggers seasonal changes in behavior. The seasonality of symptoms and the efficacy of light therapy suggest involvement of the circadian pacemaker in seasonal affective disorder (SAD), winter type. In this study, circadian pacemaker characteristics of SAD patients were compared with those of controls. Seven SAD patients and matched controls were subjected to a 120-h forced desynchrony protocol, in which core body temperature and melatonin secretion profiles were measured for the characterization of circadian pacemaker parameters. During this protocol, which enables the study of unmasked circadian pacemaker characteristics, subjects were exposed to six 20-h days in time isolation. Patients participated twice in winter (while depressed and while remitted after light therapy) and once in summer. Controls participated once in winter and once in summer. Between the SAD patients and controls, no significant differences were observed in the melatonin-derived period or in the phase of the endogenous circadian temperature rhythm. The amplitude of this rhythm was significantly smaller in depressed and remitted SAD patients than in controls. No abnormalities of the circadian pacemaker were observed in SAD patients. A disturbance in thermoregulatory processes might explain the smaller circadian temperature amplitude in SAD patients during winter.

EEG and subjective sleepiness during extended wakefulness in seasonal affective disorder: circadian and homeostatic influences

BACKGROUND

Seasonal affective disorder (SAD) may reflect a disturbance of circadian phase relationships or a disturbance of sleep-wake dependent processes, both of which change daytime energy and sleepiness levels.

METHODS

Under the unmasking conditions of a 40-hour constant routine protocol (CR), self-rated sleepiness and waking electroencephalogram (EEG) power density were assessed in women with SAD (n = 8) and in age-matched healthy control subjects (n = 9).

RESULTS

There was no significant effect of season or light treatment in any of the measures. The time course of subjective sleepiness was characterized by a circadian modulation and an overall increase during extended wakefulness in both SAD patients and control subjects. A prominent circadian rhythm of subjective sleepiness was not different in SAD patients and control subjects; however, the progressive buildup of sleepiness, as quantified by nonlinear regression analysis, was significantly reduced in SAD patients, mainly because they were sleepier than control subjects during the first 12 hours of the CR. The time course of waking EEG theta-alpha activity showed a more rapid increase during the first 10 hours of the CR in SAD patients. In contrast to control subjects who showed a progressive increase in the course of the 40-hour episode of extended wakefulness, EEG theta-alpha activity in SAD patients did not further increase over the remainder of the CR.

CONCLUSIONS

The data suggest that SAD patients may have a trait (rather than state) deficiency in the homeostatic buildup of sleep pressure during extended wakefulness as indexed by subjective sleepiness and EEG theta-alpha activity.