Circadian rhythms in multiple unit activity inside and outside the suprachiasmatic nucleus in the diurnal chipmunk (Eutamias sibiricus)

In the siberian chipmunk, a diurnal rodent, a pair of bipolar electrodes were implanted bilaterally near the suprachiasmatic nucleus (SCN). Long-term simultaneous recordings of multiple unit activity (MUA) inside and outside the SCN revealed diurnal rhythms inside the SCN that showed a daytime peak in activity during a 24 h light-dark cycle (LD 12:12). These rhythms persisted during constant darkness. MUA outside the SCN and overt behavior showed circadian rhythms that paralleled MUA inside the SCN. No phase reversal similar to that found in the nocturnal rat was observed.