Abstract
Rationale and objectives In monkeys, the muscarinic cholinergic receptor antagonist scopolamine is known to broadly disrupt learned behaviors, though the precise nature of the cognitive deficits has been questioned. Experimentally observable deficits in memory can be ascribed to poor attentional focusing, human interference as well as age, sex, and dosing regimen. The potential stress associated with isolation can also play a role during behavioral testing, particularly in small nonhuman social primates like marmosets. In this study, we examine the effects of scopolamine in marmosets using a testing approach that plausibly reduces common stressors in marmosets by minimizing transport, handling, isolation and human interference. Methods Using a custom designed home-cage touchscreen-based testing system, we investigated the influence of scopolamine on the performance on a visual associative learning task. During self-paced, voluntary testing, monkeys learned to discriminate pairs of complex visual patterns through trial and error by touching the stimulus associated with reward. Results and conclusions Eight marmosets (male and female) attained over 75% discrimination accuracy within three days of home-cage testing. The averaged data indicated no effect of acute or chronic scopolamine injections on learning rates. However, trial-level modeling of choice behavior revealed subtle age- and sex-specific deficits in performance accuracy that were not apparent in the aggregate measures. These findings highlight the value of home-cage testing combined with trial-level analysis for detecting nuanced behavioral effects of scopolamine.