Circadian phase and period responses to light stimuli in two nocturnal rodents.

We report period response curves (tauRC) for two nocturnal Murid species from India, Mus booduga and Mus platythrix. We further discuss the method of phase shift estimation in the presence of tau-changes, because such changes pose a serious methodological problem in the estimation of phase shifts. Although the tauRC indicates that most of the phase shifts are associated with small changes in tau, the period changes across all the phases showed a significant positive correlation with the phase shifts. We conclude that tauRCs are a reality even in nocturnal mammals, although their amplitude is less than what is usually found in diurnal mammals, and requires a larger data set to be distinguished from noise.