Repeated acquisition of behavioral chains: effects of methylphenidate and imipramine.

A method involving repeated acquistion of behavioral chain was used to assess the effects of methylphenidate and imipramine in individual animals. Pigeons obtained food for completing a 4-response chain, which was changed from session to session. Learning was defined by the decrease in errors across trials within a session; overall accuracy was measured by total errors per session. For comparison, the drug tests were also conducted under a performance condition, in which the 4-response chain was the same from session to session. In general, both drugs increased total errors per session as a function of dose under both the learning and performance conditions. The error-increasing effect was greater with imipramine than with methylphenidate and was detected at lower doses under the learning condition than under the performance condition. Under the learning condition, the higher doses of both drugs decreased the rate of within-session error reduction. Although neither drug enhanced accuracy at any of the doses tested, the lower doses of methylphenidate slightly decreased total trial time under both the learning and performance conditions.