PubMed Health⌕ Search

Biomedical subjects

J F Duffy

Publications and source records attributed to J F Duffy.

31 records · Page 2Linked to original sources
PubMed1997

Human circadian pacemaker is sensitive to light throughout subjective day without evidence of transients.

Fifty-six resetting trials were conducted across the subjective day in 43 young men using a three-cycle bright-light (approximately 10,000 lx). The phase-response curve (PRC) to these trials was assessed for the presence of a "dead zone" of photic insensitivity and was compared with another three-cycle PRC that had used a background of approximately 150 lx. To assess possible transients after the light stimulus, the trials were divided into 43 steady-state trials, which occurred after several baseline days, and 13 consecutive trials, which occurred immediately after a previous resetting trial. We found that 1) bright light induces phase shifts throughout subjective day with no apparent dead zone; 2) there is no evidence of transients in constant routine assessments of the fitted temperature minimum 1-2 days after completion of the resetting stimulus; and 3) the timing of background room light modulates the resetting response to bright light. These data indicate that the human circadian pacemaker is sensitive to light at virtually all circadian phases, implying that the entire 24-h pattern of light exposure contributes to entrainment.

Adult↗
PubMed1996

Phase-shifting human circadian rhythms: influence of sleep timing, social contact and light exposure.

1. Both the timing of behavioural events (activity, sleep and social interactions) and the environmental light-dark cycle have been reported to contribute to entrainment of human circadian rhythms to the 24 h day. Yet, the relative contribution of those putative behavioural synchronizers to that of light exposure remains unclear. 2. To investigate this, we inverted the schedule of rest, sedentary activity and social contact of thirty-two young men either with or without exposure to bright light. 3. On this inverted schedule, the endogenous component of the core temperature rhythm of subjects who were exposed to bright light showed a significant phase shift, demonstrating that they were adapting to the new schedule. In contrast, the core temperature rhythm of subjects who were not exposed to bright light moved on average 0.2 h later per day and after 10 days had not significantly adapted to the new schedule. 4. The direction of phase shift in the groups exposed to bright light was dependent on the time of bright light exposure, while control subjects drifted to a later hour regardless of the timing of their schedule of sleep timing, social contact and meals. 5. These results support the concept that the light-dark cycle is the most important synchronizer of the human circadian system. They suggest that inversion of the sleep-wake, rest-activity and social contact cycles provides relatively minimal drive for resetting the human circadian pacemaker. 6. These data indicate that interventions designed to phase shift human circadian rhythms for adjustment to time zone changes or altered work schedules should focus on properly timed light exposure.

Adult↗
PubMed1996

Dose-response relationships for resetting of human circadian clock by light.

Since the first report in unicells, studies across diverse species have demonstrated that light is a powerful synchronizer which resets, in an intensity-dependent manner, endogenous circadian pacemakers. Although it is recognized that bright light (approximately 7,000 to 13,000 lux) is an effective circadian synchronizer in humans, it is widely believed that the human circadian pacemaker is insensitive to ordinary indoor illumination (approximately 50-300 lux). It has been proposed that the relationship between the resetting effect of light and its intensity follows a compressive nonlinear function, such that exposure to lower illuminances still exerts a robust effect. We therefore undertook a series of experiments which support this hypothesis and report here that light of even relatively low intensity (approximately 180 lux) significantly phase-shifts the human circadian pacemaker. Our results clearly demonstrate that humans are much more sensitive to light than initially suspected and support the conclusion that they are not qualitatively different from other mammals in their mechanism of circadian entrainment.

Adult↗
PubMed1996

Gender differences in the temporal organization of proclactin (PRL) secretion: evidence for a sleep-independent circadian rhythm of circulating PRL levels- a clinical research center study.

Although a nocturnal rise in PRL secretion is well known, it has long been presumed to be evoked by sleep. To determine whether PRL secretion was driven by a sleep-independent circadian rhythm, we studied 12 men and 10 women using a constant routine protocol. Under the constant routine conditions of continuous semirecumbent wakefulness in constant indoor room light with hourly meals distributed throughout the day and night, a persistent circadian rhythm of PRL secretion was present in men and in women at the follicular and luteal phases of the menstrual cycle. Furthermore, the amplitude of this rhythm in women was significantly greater than that in men. The present data demonstrate the presence of a robust sleep-independent endogenous circadian rhythm of PRL secretion in humans. We hypothesize that this endogenous component of the circadian rhythm of PRL secretion together with those of body temperature, urine production, and cortisol, TSH, and melatonin secretion are driven by the central circadian pacemaker located in the suprachiasmatic nucleus of the hypothalamus.

Adult↗
PubMed1994

Sensitivity of the human circadian pacemaker to moderately bright light.

The aim of the present study was to evaluate the sensitivity of the human circadian pacemaker to the resetting effect of moderately bright light (approximately 1260 lux), and to assess the direct effect of such light exposure by comparison to a control group of subjects undergoing the same behavioral manipulations but with a similarly timed exposure to darkness instead of light. Endogenous circadian phase and amplitude were assessed in dim light (approximately 10-15 lux) before and after two consecutive series of three 5-hr exposures to approximately 1260 lux or to darkness (approximately 0.03 lux) in two different groups of young healthy men, using the constant-routine technique. The light or darkness exposure was centered 1.5 hr after the initial fitted endogenous temperature minimum and 12 hr opposite the newly scheduled midpoint of the sleep episode, in order to induce a phase advance in the light-exposed subjects. The phase of the endogenous circadian pacemaker was assessed by a dual-harmonic regression model from core body temperature recorded every minute during constant routines. Urinary volume was measured at each micturition, subjective alertness every 20 min, and cognitive performance hourly. The endogenous circadian phase shifted to a significantly earlier time after each series of light exposures in the treatment group than it did in the control group (two-way analysis of variance for repeated measures: F = 67.91, p = 0.0001). The analysis of circadian curves of urine production, subjective alertness, and cognitive performance scores revealed that all variables maintained stable temporal relationships with the endogenous circadian temperature minimum--an indication that these rhythms shifted in the same direction and by an equivalent amount. Despite comparable behavioral schedules, including the timing of bedrest/sleep and social contacts, circadian temperature rhythm of control subjects free-ran under dim light conditions, indicating that moderately bright light exerted a direct biological effect on the human circadian pacemaker in the treatment group. The present study also demonstrated that light of approximately 1260 lux (which is of substantially lower intensity that the approximately 7000-12,000 lux used in prior experiments) produces robust phase advances of the endogenous circadian temperature rhythm, which has been shown to be an accurate marker of the output of the circadian pacemaker (Czeisler et al., 1989). These results support the hypothesis that the phase-shifting effect of light on the human circadian pacemaker has a strongly nonlinear relationship to illuminance levels, such that it is preserved despite marked reductions in light intensity.

Adolescent↗
PubMed1992

Association of sleep-wake habits in older people with changes in output of circadian pacemaker.

Many elderly people complain of disturbed sleep patterns but there is not evidence that the need to sleep decreases with age; it seems rather that the timing and consolidation of sleep change. We tried to find out whether there is a concurrent change in the output of the circadian pacemaker with age. The phase and amplitude of the pacemaker's output were assessed by continuous measurement of the core body temperature during 40 h of sustained wakefulness under constant behavioural and environmental conditions. 27 young men (18-31 years) were compared with 21 older people (65-85 years; 11 men, 10 women); all were healthy and without sleep complaints. The mean amplitude of the endogenous circadian temperature oscillation (ECA) was 40% greater in young men than in the older group. Older men had a lower mean temperature ECA than older women. The minimum of the endogenous phase of the circadian temperature oscillation (ECP) occurred 1 h 52 min earlier in the older than in the young group. Customary bedtimes and waketimes were also earlier in the older group, as was their daily alertness peak. There was a close correlation between habitual waketime and temperature ECP in young men, which may lose precision with age, especially among women. These findings provide evidence for systematic age-related changes in the output of the human circadian pacemaker. We suggest that these changes may underlie the common complaints of sleep disturbance among elderly people. These changes could reflect the observed age-related deterioration of the hypothalamic nuclei that drive mammalian circadian rhythms.

Adult↗
PubMed1992

Short-term memory, alertness and performance: a reappraisal of their relationship to body temperature.

Previous studies have led to the beliefs: (1) that short-term memory is best during the night when the body temperature is at its nadir, and (2) that the circadian rhythms of short-term memory and subjective alertness are driven by oscillators independent from each other and from the body temperature cycle. Unfortunately, these conclusions, which would have major implications for understanding the organization of the human circadian timing system, are largely based on field and laboratory studies, which in many cases sampled data infrequently and/or limited data collection to normal waking hours. In order to investigate these points further, we have monitored behavioural variables in two different protocols under controlled laboratory conditions: (1) during a period of 36-60 h of sustained wakefulness; and (2) during forced desynchrony between the body temperature and sleep/wake cycles, allowing testing of non-sleep-deprived subjects at all circadian phases. Contrary to earlier findings, we report here that the circadian rhythm of short-term memory varies in parallel with the circadian rhythms of subjective alertness, calculation performance, and core body temperature under both these experimental conditions. These results challenge the notion that short-term memory is inversely linked to the body temperature cycle and suggest that the human circadian pacemaker, which drives the body temperature cycle, is the primary determinant of endogenous circadian variations in subjective alertness and calculation performance as well as in the immediate recall of meaningful material.

Adolescent↗
PubMed1992

Circadian and sleep/wake dependent aspects of subjective alertness and cognitive performance.

Circadian and sleep/wake dependent processes underlying variations in subjective alertness and cognitive performance were assessed in a constant routine protocol and in a protocol in which the sleep/wake cycle was uncoupled from the output of the endogenous circadian pacemaker. In the latter protocol, the contribution of a sleep/wake dependent process and a circadian process to alertness and performance were separated by folding the data at either the period of the sleep/wake cycle or at the period of the endogenous circadian body temperature rhythm. This analysis revealed that prior wakefulness within a range of 0-18 h significantly reduced alertness and performance and that the circadian rhythm of core body temperature paralleled the circadian rhythm of alertness and performance. During the first 16 h of the constant routine protocol, which coincided with the subjects' habitual period of wakefulness, alertness and performance remained at a stable level. The latter finding was explained by assuming that during our usual waking day the circadian system counteracts the detrimental effects of increasing duration of prior wakefulness.

Adolescent↗
PubMed1991

Research on sleep, circadian rhythms and aging: applications to manned spaceflight.

Disorders of sleep and circadian rhythmicity are characteristic of both advancing age and manned spaceflight. Sleep fragmentation, reduced nocturnal sleep tendency and sleep efficiency, reduced daytime alertness, and increased daytime napping are common to both of these conditions. Recent research on the pathophysiology and treatment of disrupted sleep in older people has led to a better understanding of how the human circadian pacemaker regulates the timing of the daily sleep-wake cycle and how it responds to the periodic changes in the light-dark cycle to which we are ordinarily exposed. These findings have led to new treatments for some of the sleep disorders common to older individuals, using carefully timed exposure to bright light and darkness to manipulate the phase and/or amplitude of the circadian timing system. These insights and treatment approaches have direct applications in the design of countermeasures allowing astronauts to overcome some of the challenges which manned spaceflight poses for the human circadian timing system. We have conducted an operational feasibility study on the use of scheduled exposure to bright light and darkness prior to launch in order to facilitate adaptation of the circadian system of a NASA space shuttle crew to the altered sleep-wake schedule required for their mission. The results of this study illustrate how an understanding of the properties of the human circadian timing system and the consequences of circadian disruption can be applied to manned spaceflight.

Adult↗
PubMed1990

Exposure to bright light and darkness to treat physiologic maladaptation to night work.

Working at night results in a misalignment between the sleep-wake cycle and the output of the hypothalamic pacemaker that regulates the circadian rhythms of certain physiologic and behavioral variables. We evaluated whether such physiologic maladaptation to nighttime work could be prevented effectively by a treatment regimen of exposure to bright light during the night and darkness during the day. We assessed the functioning of the circadian pacemaker in five control and five treatment studies in order to assess the extent of adaptation in eight normal young men to a week of night work. In the control studies, on the sixth consecutive night of sedentary work in ordinary light (approximately 150 lux), the mean (+/- SEM) nadir of the endogenous temperature cycle continued to occur during the night (at 3:31 +/- 0:56 hours), indicating a lack of circadian adaptation to the nighttime work schedule. In contrast, the subjects in the treatment studies were exposed to bright light (7000 to 12,000 lux) at night and to nearly complete darkness during the day, and the temperature nadir shifted after four days of treatment to a significantly later, midafternoon hour (14:53 +/- 0:32; P less than 0.0001), indicating a successful circadian adaptation to daytime sleep and nighttime work. There were concomitant shifts in the 24-hour patterns of plasma cortisol concentration, urinary excretion rate, subjective assessment of alertness, and cognitive performance in the treatment studies. These shifts resulted in a significant improvement in both alertness and cognitive performance in the treatment group during the night-shift hours. We conclude that maladaptation of the human circadian system to night work, with its associated decline in alertness, performance, and quality of daytime sleep, can be treated effectively with scheduled exposure to bright light at night and darkness during the day.

Adaptation, Physiological↗
PubMed1990

Use of the MMPI to uncover histories of childhood abuse in adult female psychiatric patients.

Psychiatric hospital records of 182 adult females were reviewed to determine feasibility of using the MMPI to uncover repressed histories of childhood abuse. Charts with MMPI profiles that met the standard and extended Scarlett O'Hara V configurations were examined for histories of childhood sexual or physical abuse and exposure to parental alcoholism. Findings were compared with a representative sample of control patients who did not have Scarlett O'Hara V configurations. Results showed that the MMPI can help detect adults who as children were sexually or nonsexually abused, or had alcoholic caretakers, or a combination of the above.

Adolescent↗
PubMed1989

Bright light induction of strong (type 0) resetting of the human circadian pacemaker.

The response of the human circadian pacemaker to light was measured in 45 resetting trials. Each trial consisted of an initial endogenous circadian phase assessment, a three-cycle stimulus which included 5 hours of bright light per cycle, and a final phase assessment. The stimulus induced strong (type 0) resetting, with responses highly dependent on the initial circadian phase of light exposure. The magnitude and direction of the phase shifts were modulated by the timing of exposure to ordinary room light, previously thought to be undetectable by the human pacemaker. The data indicate that the sensitivity of the human circadian pacemaker to light is far greater than previously recognized and have important implications for the therapeutic use of light in the management of disorders of circadian regulation.

Adult↗