Behavioural experiments in mice are often carried out during the resting phase of these nocturnal animals. Ignoring the fact that mice are more active during the dark period, results from resting-phase testing has also been used to characterize these animals. Since the influence of the light/dark cycle on testing is likely to be a relevant factor for the analysis of behavioural results, the aim of this study was to evaluate the effects of the relative time of the day as well as light conditions during testing on behavioural and cognitive performance in inbred mice. Naïve DBA/2N (DBA) mice were tested in the modified hole board (mHB) either during the dark phase under red light or during the light phase under white light. Different behavioural dimensions and cognitive functions were evaluated in parallel. Depending on the testing conditions, the results showed significant differences in behavioural activity, with DBA mice being less inhibited during dark phase. The same experimental group made fewer memory errors in a visuo-spatial task and showed a faster habituation compared with the group tested during the dark phase. From the results we conclude that testing during the light phase induces a pronounced behavioural inhibition as well as a cognitive disruption in DBA mice, which should be taken into account when cognitively testing these animals.
