Efficacy of a single sequence of intermittent bright light pulses for delaying circadian phase in humans

Abstract

It has been shown in animal studies that exposure to brief pulses of bright light can phase shift the circadian pacemaker and that the resetting action of light is most efficient during the first minutes of light exposure. In humans, multiple consecutive days of exposure to brief bright light pulses have been shown to phase shift the circadian pacemaker. The aim of the present study was to determine whether a single sequence of brief bright light pulses administered during the early biological night would phase delay the human circadian pacemaker. Twenty-one healthy young subjects underwent a 6.5-h light exposure session in one of three randomly assigned conditions: 1) continuous bright light of ∼9,500 lux, 2) intermittent bright light (six 15-min bright light pulses of ∼9,500 lux separated by 60 min of very dim light of <1 lux), and 3) continuous very dim light of <1 lux. Twenty subjects were included in the analysis. Core body temperature (CBT) and melatonin were used as phase markers of the circadian pacemaker. Phase delays of CBT and melatonin rhythms in response to intermittent bright light pulses were comparable to those measured after continuous bright light exposure, even though the total exposure to the intermittent bright light represented only 23% of the 6.5-h continuous exposure. These results demonstrate that a single sequence of intermittent bright light pulses can phase delay the human circadian pacemaker and show that intermittent pulses have a greater resetting efficacy on a per minute basis than does continuous exposure.

Addition of a non-photic component to a light-based mathematical model of the human circadian pacemaker

“…With the inclusion of this factor, Equation 1 is replaced by (9) The inclusion of this logistic function gives α a proportionality of I 1.5 for values well below I = 100, which is comparable to the proportionality of I 1.42 that Zeitzer et al (2000) fit to low I in their intensity response curve. Recently, Gronfier et al (2004) published data from the 1-Pulse Intermittent Light Protocol (described above) that permit a more accurate assessment of the dynamics embodied in Process L. Most importantly, the forward rate parameter, α 0 , was found to be significantly higher than had been proposed earlier . Small changes have also been incorporated in β and G. The revised parameters are α 0 = 0.1 min −1 , β = 0.007 min −1 and G = 37.…”

“…The intrinsic periods determined from these protocols were used as the input parameter, τ x (Equation 5), for simulations of our model. Gronfier et al (2004) performed a series of experiments to determine the response of the pacemaker to a single sequence of intermittent bright light pulses compared to a continuous bright light or dim light pulse. In these experiments, subjects were scheduled to two 24.0-h days in ~90 lux followed by a 26.2-h CR.…”

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

“…After CR2, subjects were scheduled to a sleep-wake cycle at the same between CBT min and habitual bedtime as that measured in CR1, such that CBTminCR1 ϭ CBTminCR2 . MEL on and MEL off were calculated by using a least-square regression analysis and a threshold of 25% of the peak-to-trough amplitude (4). Phase angle of entrainment was calculated as the difference in time between lights off (bedtime) and MEL on ( MELon ) and between lights on (waketime) and MEL off ( MELoff ).…”

“…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)(3)(4)(5)(6)(7). In totally blind people, the circadian timekeeping system often loses synchrony with the earth's 24-h light:dark cycle (8).…”

Modelling ‘non-visual’ effects of daylighting in a residential environment

“…This statement should come with some reservations, however, as our model does not account for the non-linearity of light duration with circadian response, as noted in sections 2 and 3.2. It has been found, for instance, that the first 15 mins of an exposure is more effective than the last 15 mins: [60] examined the effects of 6.5 h continuous bright white light at night versus 15 mins light every 75 mins. Even though the intermittent exposure represented 20% of the light duration, it induced 75% of the phase resetting response.…”