Continuous light abolishes the maternal entrainment of the circadian activity rhythm of the pups in the field mouse.

12:12-h cycles of presence and absence of mother mouse act as a 'zeitgeber' and entrain the circadian rhythm of locomotor activity in the pups of Mus booduga under continuous darkness or continuous dim light. Continuous higher illumination of 15-25 lx abolishes this impressive maternal entrainment.