Precision of a mammalian circadian clock

This paper reports study of day-to-day instability in the locomotor activit y rhythm of the nocturnal field mouse Mus booduga. The free-running period ( tau) of this rhythm was estimated in constant darkness in n=347 adult mal e mice. The "onset" and "offset" of locomotor activity rhythm were used as phase markers of the circadian clock. The precision of the onset of locomot or activity was observed to be a non-linear function of tau, with maximal p recision at tau close to 24 h. The precision of the offset of locomotor act ivity was found to increase with increasing tau. These results suggest that the homeostasis of tau is tighter when tau is close to 24 h.