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

Abstract

Several theories propose that interval timing and memory share common cognitive mechanisms. Pharmacological disruption of the cholinergic system using scopolamine, a muscarinic acetylcholine receptor antagonist, is widely used as a model of cognitive impairment. However, its effects on temporal prediction remain poorly understood. Previous timing studies in freely moving animals are difficult to interpret because motor activity may confound measures of interval timing. Here, we investigated the effects of systemic scopolamine administration on temporal prediction in mice using a head-fixed behavioral paradigm. Mice were trained on a fixed-time schedule task using a peak procedure, in which a 10% sucrose solution was delivered every 10 s through a spout positioned within licking distance. After training, mice developed anticipatory licking responses that peaked around the expected reward time, demonstrating temporal prediction of reward delivery. Systemic administration of scopolamine increased the variability of temporal prediction in a dose-dependent manner without altering the mean peak time. Trial-by-trial analysis further revealed that scopolamine reduced the duration of licking bouts while preserving the total number of licks during peak trials, suggesting impaired maintenance of reward-directed licking behavior rather than altered reward consumption. In a separate open-field assay, scopolamine increased spontaneous locomotor activity and reduced fecal output. These findings demonstrate that cholinergic blockade disrupts the precision of temporal prediction and alters behavioral organization in mice. The increased variability in timing behavior following scopolamine administration may reflect impaired regulation of transitions between behavioral states, providing new insights into the role of cholinergic signaling in temporal cognition.