Circadian phase resetting by a single short-duration light exposure

Apr 14, 2017JCI insight

Resetting the body’s internal clock with a brief light exposure

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Abstract

A single 15-second light pulse can cause a median phase delay shift of -34.8 minutes in the human circadian pacemaker.

Both 15-second and 2-minute light exposures during the biological night resulted in significant phase delays compared to dim light control conditions.
The 2-minute exposure induced a median phase delay shift of -45.4 minutes, which was not significantly different from the shift caused by the 15-second exposure.
Control conditions led to an advance shift of +22.3 minutes, highlighting the contrasting effects of light exposure duration on circadian timing.
Findings confirm a nonlinear relationship between light exposure duration and the magnitude of phase shift in the human circadian system.
The results suggest sensitivity of the circadian pacemaker to brief light stimuli at night, which may impact circadian rhythm disruption.

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In humans, a single light exposure of 12 minutes and multiple-millisecond light exposures can shift the phase of the circadian pacemaker. We investigated the response of the human circadian pacemaker to a single 15-second or 2-minute light pulse administered during the biological night.Twenty-six healthy individuals participated in a 9-day inpatient protocol that included assessment of dim light melatonin onset time (DLMO time) before and after exposure to a single 15-second (= 8) or 2-minute (= 12) pulse of bright light (9,500 lux; 4,100 K fluorescent) or control background dim light (<3 lux;= 6). Phase shifts were calculated as the difference in clock time between the two phase estimates.Both 15-second and 2-minute exposures induced phase delay shifts [median (± SD)] of -34.8 ± 47.2 minutes and -45.4 ± 28.4 minutes, respectively, that were significantly (= 0.04) greater than the control condition (advance shift: +22.3 ± 51.3 minutes) but were not significantly different from each other. Comparisons with historic data collected under the same conditions confirmed a nonlinear relationship between exposure duration and the magnitude of phase shift.Our results underscore the exquisite sensitivity of the human pacemaker to even short-duration single exposures to light. These findings may have real-world implications for circadian disruption induced by exposure to brief light stimuli at night.The study was registered as a clinical trial on www.clinicaltrials.org, NCT #01330992.Funding for this study was provided by NSBRI HFP02802 and NIH P01-AG09975, R01-HL114088 (EBK), RC2-HL101340-0 (EBK, SWL, SAR, REK), K02-HD045459 (EBK), K24-HL105664 (EBK), T32-HL07901 (MSH, SAR), HL094654 (CAC), and AG044416 (JFD). The project described was supported by NIH grant 1UL1 TR001102-01, 8UL1TR000170-05, UL1 RR 025758, Harvard Clinical and Translational Science Center, from the National Center for Advancing Translational Science. BACKGROUND. METHODS. RESULTS. CONCLUSIONS. TRIAL REGISTRATION. FUNDING. n n n P

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Circadian phase resetting by a single short-duration light exposure

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