PHASE-AMPLITUDE RESETTING OF THE HUMAN CIRCADIAN PACEMAKER VIA BRIGHTLIGHT - A FURTHER ANALYSIS

We present here an analysis of strong, weak, and critical bright-light resetting trials in humans, and report not only phase but also amplit ude data for the first time. For this analysis, an appropriate iterati ve smoothing procedure for phase transition curves is introduced, in w hich the data are sequenced so as to minimize the perpendicular distan ce from the data to the smoothed fit. From these smoothed data, we cre ate polar phase-amplitude resetting-maps.(PARMs) in order to fully. il lustrate the effects of the resetting stimuli on both circadian amplit ude and phase, and thereby to determine whether these resetting result s can be decribed by a phase-only model or whether a phase-amplitude m odel is required. Our results indicate that a single 5-hr episode of b right light induces weak type 1 resetting of the human circadian pacem aker. Two cycles of exposure to the same stimulus on consecutive days induce critical resetting, in which significant amplitude reduction ma y be observed. A three-cycle stimulus induces strong type 0 resetting- with different effects-on circadian amplitude, depending on the initia l phase of the stimulus application. When a three-cycle stimulus is ce ntered near the nadir of the temperature cycle, large phase shifts are achieved via amplitude suppression. However, when this stimulus is ce ntered away from the temperature nadir, smaller phase shifts are achie ved in which both small increases and small decreases in circadian amp litude are observed. These data indicate that the human circadian pace maker is not a simple, phase-only oscillator. Instead, a full descript ion of human circadian resetting responses to light requires analysis of both phase and amplitude data-a finding that is consistent with a p hase-amplitude model of the circadian resetting mechanism.