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

TY - JOUR

T1 - Accuracy of Human Circadian Entrainment under Natural Light Conditions

T2 - Model Simulations

AU - Beersma, Domien G.M.

AU - Spoelstra, Kamiel

AU - Daan, Serge

PY - 1999/12

Y1 - 1999/12

N2 - 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.

AB - 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.

KW - circadian system

KW - entrainment

KW - light

KW - model

KW - twilight

KW - zeitgeber

U2 - 10.1177/074873099129000858

DO - 10.1177/074873099129000858

M3 - Article

C2 - 10643749

AN - SCOPUS:84990328214

SN - 0748-7304

VL - 14

SP - 525

EP - 532

JO - Journal of Biological Rhythms

JF - Journal of Biological Rhythms

IS - 6

ER -