Light Effects on Human Circadian Rhythms: A Review of Recent Andechs Experiments

Entrainment of the circadian pacemaker to the light:dark cycle is necessary for rhythmic physiological functions to be appropriately timed over the 24-h day. Nonentrainment results in sleep, endocrine, and neurobehavioral impairments. Exposures to intermittent bright light pulses have been reported to phase shift the circadian pacemaker with great efficacy. Therefore, we tested the hypothesis that a modulated light exposure (MLE) with bright light pulses in the evening would entrain subjects to a light:dark cycle 1 h longer than their own circadian period ( ). Twelve subjects underwent a 65-day inpatient study. Individual subject's circadian period was determined in a forced desynchrony protocol. Subsequently, subjects were released into 30 longer-than-24-h days (daylength of ؉ 1 h) in one of three light:dark conditions: (i) Ϸ25 lux; (ii) Ϸ100 lux; and (iii) MLE: Ϸ25 lux followed by Ϸ100 lux, plus two 45-min bright light pulses of Ϸ9,500 lux near the end of scheduled wakefulness. We found that lighting levels of Ϸ25 lux were insufficient to entrain all subjects tested. Exposure to Ϸ100 lux was sufficient to entrain subjects, although at a significantly wider phase angle compared with baseline. Exposure to MLE was able to entrain the subjects to the imposed sleep-wake cycles but at a phase angle comparable to baseline. These results suggest that MLE can be used to entrain the circadian pacemaker to non-24-h days. The implications of these findings are important because they could be used to treat circadian misalignment associated with space flight and circadian rhythm sleep disorders such as shiftwork disorder.light ͉ melatonin ͉ phase angle of entrainment ͉ phase response curve ͉ sleep Entrainment of a circadian rhythm by a zeitgeber fulfills biological purpose in providing a very distinct phase relationship between the periodicity of the organism and that of the environment.J. Aschoff (1) T o be of functional significance for the organism, circadian rhythms must be entrained to the 24-h day. For nearly all species studied, the light:dark cycle is the most powerful circadian synchronizer. The resetting capacity of light depends on its intensity, timing, duration, temporal pattern, and spectral composition (2-7). In totally blind people, the circadian timekeeping system often loses synchrony with the earth's 24-h light:dark cycle (8). Well described in animals (9-11) and only recently confirmed in humans (12), entrainment of the circadian system depends on (i) its intrinsic period ( ), (ii) the light:dark cycle to which it is exposed (T; T-cycle), and (iii) the strength of the entraining stimulus (zeitgeber, from German for "time giver"). The generally accepted nonparametric model of circadian entrainment predicts immediate phase shifting in response to light, according to a phase response curve (PRC) (3, 9, 13). In humans, for whom the intrinsic period is on average Ϸ24.2 h (14), entrainment to the solar day of earth (T ϭ 24 h) requires that the biological clock be ''reset'' by on average of Ϸ0.2 h per day in th...

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“…The scalloping of the MEL on observed across the FD protocol (Fig. 2) is consistent with relative coordination (20,21). Fig.…”

Section: Resultssupporting

confidence: 65%

Entrainment of the human circadian pacemaker to longer-than-24-h days

Gronfier

Wright

Kronauer

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

185

143

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“…This finding supported the need for a long, protected sleep period for watchstanders. Additionally, work by both Aschoff et al (1971) and Wever (1983Wever ( , 1989 had shown that non-photic Zeitgebers that include a disciplined, regular sleep-wake cycle entrained the body's circadian rhythms to a 24-hour period.…”

Section: Scientific Rationalementioning

confidence: 99%

Effects of Three Watchstanding Schedules on Submariner Physiology, Performance and Mood

Miller¹,

Dyche²,

Cardenas³

et al. 2003

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“…Dessa forma, entende-se que além dos fotorreceptores clássicos, responsáveis pela fototransdução, a melanopsina, expressa por células ganglionares, é um importante fotopigmento para o processo de arrastamento da luz em respostas circadianas, ou respostas diária de ciclo claro--escuro (Duffy & Wright, 2005;Evans, Elliott, & Gorman, 2007;Glickman et al, 2012;Hannibal, 2002;Hatori & Panda, 2010;Hattar, Liao, Takao, Berson, & Yau, 2002;Rea, Figueiro, Bierman, & Bullough, 2010;Wever, 1989). Por exemplo, Pickard, Ralph e Menaker (1987) utilizaram feixes de luz focada na fóvea em diferentes momentos do dia e perceberam que esse estímulo provoca uma variação de resposta periódica com amplitudes e fases diferentes (Pickard et al, 1987).…”

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Influência do Cronotipo e do Horário da Medida na Sensibilidade ao Contraste Visual

Andrade¹,

Silva²,

Santos³

2015

Psicol. Reflex. Crit.

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ResumoEste estudo teve como objetivo avaliar a curva de sensibilidade ao contraste para estímulos de grades senoidais verticais de frequências espaciais de 0,2; 0,6; 1; 3,1; 6,1; 8,8; 13,2 e 15,6 ciclos por grau de ângulo visual; em um ritmo de 24 horas de adultos saudáveis de diferentes cronotipos. Participaram desta pesquisa 18 voluntários do sexo masculino com idade de 19 a 31 anos (M=23,8; DP=3,29 AbstractThis study aimed to evaluate the contrast sensitivity curve for the stimuli of vertical sinusoidal grids with spatial frequencies of .2; .6; 1; 3.1; 6.1; 8.8; 13.2 and 15.6 cycles per degree of visual angle, in a 24-hour rhythm of healthy adults of different chronotypes. This study had 18 participants aged 19 to 31 years (M=23.8; SD=3.29) divided into groups according to the chronotype: Morningness (n=5), Intermediate (n=9) and Moderate Eveningness (n=4). Neuropsychological measures and the Metropsis software were used to evaluate the Contrast Sensitivity Function (CSF). CSF measurements were performed by the psychophysical method of forced choice between two spatial alternatives. Results showed signifi cant changes in the dimensions related to cognitive processing and CSF for morning subjects [F (14; 76303) The study concluded that contrast sensitivity is an important aspect to the study of circadian visual perception, suggesting that the sensorial mechanisms which process visual contrast are directly related to the time and pattern of people's chronotypes.

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Light Effects on Human Circadian Rhythms: A Review of Recent Andechs Experiments

Cited by 172 publications

References 30 publications

Entrainment of the human circadian pacemaker to longer-than-24-h days

Entrainment of the human circadian pacemaker to longer-than-24-h days

Effects of Three Watchstanding Schedules on Submariner Physiology, Performance and Mood

Influência do Cronotipo e do Horário da Medida na Sensibilidade ao Contraste Visual

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