Accuracy of Human Circadian Entrainment under Natural Light Conditions: Model Simulations

Author:

Beersma Domien G. M.1,Spoelstra Kamiel,Daan Serge2

Affiliation:

1. Zoological Laboratory, University of Groningen, PO Box 14, 9750 AA Haren; Department of Biological Psychiatry; PO Box 30.001, 9700 RB, Groningen, the Netherlands

2. Zoological Laboratory, University of Groningen, PO Box 14, 9750 AA Haren, the Netherlands

Abstract

The patterns of light intensity to which humans expose their circadian pacemakers in daily life are very irregular and vary greatly from day to day. The circadian pacemaker can adjust to such irregular exposure patterns by daily phase shifts, such as summarized in a phase response curve. It is demonstrated in this paper on the basis of computer simulations applying actually recorded human light exposure patterns that the pacemaker can substantially improve its accuracy by an additional response to light: For that purpose, it should additionally change its angular velocity (and consequently its period [.tau]) in response to light. Reductions of [.tau] in response to light in the morning and increases of [.tau] in response to light in the evening can lead to an increase in entrained pacemaker accuracy with about 25%. Circadian pacemakers have evolved as accurate internal representations of external time, and investigated diurnal mammals all seem to respond to light by changing the period of their circadian pacemaker (in addition to shifting phase). The authors suggest that also human circadian systems take advantage of this possibility and that their pacemakers respond to light by shifting phase and changing period. As a consequence of this postulated mechanism, the simulations demonstrate that the period of the pacemaker under normally entrained conditions is 24 h. The maximum accuracy corresponds to a day-to-day standard deviation of the time of phase 0 of circa 15 min. This is considerably more accurate than the light signal humans usually perceive.

Publisher

SAGE Publications

Subject

Physiology (medical),Physiology

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