Time to switch off lights? Effects of testing moment in the circadian sleep-wake rhythm

The daily light-dark cycle allows the synchronization of behavioural and physiological processes to the external environment. Light is the most important environmental cue or zeitgeber that coordinate many aspects of physiology and behaviour such as activity, maintenance behaviours, alertness, body temperature, hormonal regulation or long-term potentiation (i.e. a process that plays a key role in memory consolidation). Mice are among the main animals used in behavioural neuroscience and preclinical research laboratories. Although they are nocturnal animals, mice are generally tested during day (i.e. their resting phase). Thus, the testing moment might be a predominant variable that can affect animal behaviour and cognition and from there, all the inferences we make about behavioural and cognitive processes.
In this study, several behavioural and cognitive components such as activity, motivation, learning and behavioural flexibility have been evaluated. We assumed that C57/BL6 mice should perform better and show higher activity rate while tested during night. Although we didn’t find any differences between testing conditions in behavioural or cognitive performance, several factors can explain this absence of effects such as nature of the task, presence of zeitgeber, modulation of arousal, light pollution as well as light conditions during the test itself.