The effects of atropine, benactyzine, and physostigmine on a repeated acquisition baseline in monkeys

A repeated acquisition procedure was used with cynomolgus monkeys to test the effects of one anticholinesterase (physostigmine) and two anticholinergic (atropine and benactyzine) compounds on learning and performance. Learning was defined as the number of response chains (trials) required to meet a criterion of three consecutive chains at 90% accuracy or better. Measures were the number of trials to criterion and the number of errors made. Following learning, behavior was analyzed as performance. Measures were total errors after learning and errors per trial. Time-out minutes (i.e., periods of enforced no responding after errors) were analyzed separately from total session time. Atropine (0.014, 0.044, 0.14, and 0.44 mg/kg) produced large learning disruptions and performance decrements at the highest dose. Learning decrements due to benactyzine (0.057, 0.18, 0.57, and 1.82 mg/kg) were not significant and produced little effect on performance. The effect of physostigmine (0.025, 0.050, and 0.075 mg/kg on learning was not consistent. The anticholinergics increased performance errors per trial, while the anticholinesterase had little effect. Session times showed dose-related increases for all drugs and were significantly increased by the highest doses of each. The session time increases observed after the anticholinergics were interpreted to be due to both an effect on learning and an effect on response rate, whereas the anticholinesterase effect was due primarily to response suppression.