Bright light therapy: Improved sensitivity to its effects on rest-activityrhythms in Alzheimer patients by application of nonparametric methods

Sleep-wake rhythm disturbances in patients with Alzheimer's disease (AD) ma ke a strong demand on caregivers and are among the most important reasons f or institutionalization. Several previous studies reported that the disturb ances improve with increased environmental Light, which, through the retino hypothalamic tract, activates the suprachiasmatic nucleus (SCN), the biolog ical clock of the brain. The data of recently published positive and negati ve reports on the effect of bright Fight on actigraphically assessed rest-a ctivity rhythms in demented elderly were reanalyzed using several statistic al procedures. It was demonstrated that the light-induced improvement in co upling of the rest-activity rhythm to the environmental zeitgeber of bright light is better detected using nonparametric procedures. Cosinor, complex demodulation, and Lomb-Scargle periodogram-derived variables are much less sensitive to this effect because of the highly nonsinusoidal waveform of th e rest-activity rhythm. Guidelines for analyses of actigraphic data are giv en to improve the sensitivity to treatment effects in future studies.