Systemic injection of scopolamine increased the variability of temporal prediction in head-fixed mice.

Several theories propose a close relationship between interval timing and the temporal properties of memory. Systemic administration of scopolamine, a muscarinic acetylcholine receptor antagonist, is known to induce memory deficits and impair temporal prediction. However, existing studies on timing using free-moving animals are challenging to interpret due to the confounding effects of movement on interval timing. In this study, we examined the effects of scopolamine on timing behavior in mice using a head-fixed experimental setup. Mice were trained on a fixed-time schedule task with a peak procedure, where a 10% sucrose solution was delivered every 10 seconds through a spout placed within the licking distance of the mice. Following training, the mice exhibited anticipatory licking behavior in response to the timing of sucrose delivery, indicating that they could predict the reward timing. Systemic administration of scopolamine increased the variability of temporal prediction in a dose-dependent manner but did not affect the mean temporal prediction. Single-trial bout analysis revealed that scopolamine impaired the duration of licking bouts without affecting the total number of licks in peak trials, suggesting that the mice were unable to sustain licking at the spout. Additionally, we assessed the effects of scopolamine on spontaneous locomotor activity and excretion in a free-moving open-field task. Scopolamine injections increased locomotor activity and decreased fecal output. Taken together, these findings suggest that the increased variability in timing behavior induced by scopolamine may be attributed to changes in transitions between behavioral states.