In both diurnal (left) and nocturnal (right) mammals, SCN activity (orange halos around neurons) is higher during the day (top, larger halos) than at night (bottom, smaller halos). In the R. pumilio SCN (left side) – but not in the mouse SCN (right side) – one out of three neurons (in magenta) shows a prolonged resting phase after inhibitory stimuli. This resting phase delays action potential firing, the frequency of which is shown in a simplified scheme on the upper left corner of each panel. This ‘brake’ to SCN excitability operates irrespective of the time of day, leading to reduced activity in the SCN of R. pumilio overall (left panels, smaller halos) while maintaining distinct excitation patterns between day and night. This activity pattern is likely an adaptation for diurnality.