Interval timing in mice does not rely upon the circadian pacemaker.

The suprachiasmatic nucleus (SCN) of the hypothalamus is a precise timekeeper that controls and synchronizes the circadian period of countless physiological and behavioural functions and entrains them to the 24 h light/dark cycle. We examined the possibility that it is also indirectly involved in measurement of a briefer interval by observing the effects of lesions targeted at the SCN, and abolishing circadian rhythmicity, upon interval timing behaviour. Fourteen house mice (Mus musculus) were trained to estimate a 10 s interval using a modified peak procedure, and then underwent electrolytic lesions. Six individuals became behaviourally arrhythmic. Peak interval performance was then assessed in 12:12 light/dark conditions and in constant darkness. No significant change in peak characteristics was observed as a consequence of the lesion for either rhythmic or arrhythmic groups. These results show that the accurate measurement of 10 s requires neither a functioning circadian pacemaker nor entrained behavioural rhythmicity.