Splitting of the circadian activity rhythm in common marmosets (Callithrix j. jacchus; primates)

Long-term recordings of the free-running circadian activity rhythm in common marmosets, Callithrix j. jacchus, living under constant environmental conditions (LL 200-470 lx) provided evidence of rhythm splitting in nonhuman primates. In two out of ten test animals two different types of splitting occurred; spontaneous persistent splitting and temporary splitting. Neither a reduction of the illumination intensity nor the application of dark pulses had any effect on the two activity components of the persistently split rhythm.