Failure of Extraocular Light to Facilitate Circadian Rhythm Reentrainment in Humans

Abstract

Although extraocular light can entrain the circadian rhythms of invertebrates and nonmammalian vertebrates, almost all studies show that the mammalian circadian system can only be affected by light to the eyes. The exception is a recent study by Campbell and Murphy that reported phase shifts in humans to bright light applied with fiber-optic pads behind the knees (popliteal region). We tested whether this extraocular light stimulus could accelerate the entrainment of circadian rhythms to a shift of the sleep schedule, as occurs in shift work or jet lag. In experiment 1, the sleep/dark episodes were delayed 8h from baseline for 2 days, and 3h light exposures were timed to occur before the temperature minimum to help delay circadian rhythms. There were three groups: (1) bright (about 13,000 lux) extraocular light from fiber-optic pads, (2) control (dim light, 10-20 lux), and (3) medium-intensity (about 1000 lux) ocular light from light boxes. In experiment 2, the sleep/dark episodes were inverted, and extraocular light was applied either before the temperature minimum to help delay circadian rhythms or after the temperature minimum to help advance rhythms. Circadian phase markers were the salivary dim light melatonin onset (DLMO) and the rectal temperature minimum. There was no evidence that the popliteal extraocular light had a phase-shifting effect in either experiment. Possible reasons for phase shifts in the Campbell and Murphy study and not the current study include the many differences between the protocols. In the current study, there was substantial sleep deprivation before the extraocular light was applied. There was a large shift in the sleep/dark schedule, rather than allowing subjects to sleep each day from midnight to noon, as in the Campbell and Murphy study. Also, when extraocular light was applied in the current protocol, subjects did not experience a change from sleeping to awake, a change in posture (from lying in bed to sitting in a chair), or a change in ocular light (from dark to dim light). Further research is necessary to determine the conditions under which extraocular light might produce phase shifts in human circadian rhythms.

An arousing, musically enhanced bird song stimulus mediates circadian rhythm phase advances in dim light

“…The direction and magnitude of DLMO and CBT minimum phase shifts also were positively related, demonstrating a direct effect on the circadian timing system, similar to other studies (8,18,20,23,30,39,58). DLMO occurred a little over 7 h before CBT minimum, at baseline and after exposure, with a positive relationship between the two markers, as has been reported previously (7,9,14,23).…”

Extraocular Phototransduction and Circadian Timing Systems in Vertebrates

“…A similar conclusion was reached by Eastman et al (54) based on results from a study using light exposure devices identical to those employed by Campbell and Murphy (48). Healthy young adults, the popliteal regions of whom were exposed for 3h to either about 13,000 lux or to no light, showed no systematic differences in the degree to which rhythms of salivary melatonin and body core temperature were shifted relative to baseline measures.…”

Preflight Adjustment to Eastward Travel:3 Days of Advancing Sleep with and without Morning Bright Light

“…The time between the baseline DLMO and the start of the 1st morning bright light pulse was 8.6 ± 1.5 h in the continuous light group and 9.2 ± 1.2 h intermittent light group, but these were not significantly different, [t(17) = -0.97, p = 0.35]. Several studies have shown that the average interval between the DLMO and the Tmin is 7 h (e.g., Cagnacci et al, 1996;Brown et al, 1997;Eastman et al, 2000). Thus, we estimate that the interval between the baseline Tmin and the start of the 1st bright light pulse was 1.5 to 2 h (remember wake time on 1st day of treatment was 1 h earlier than baseline).…”