Effects of scopolamine, atropine, and d-amphetamine on internal and external control of responding on non-reinforced trials.

Abstract

Rats learned not to respond on non-reinforced trials in a discrete trial situation in which trial responses were reinforced only if preceded by three or more non-response trials. Drug effects were measured: 1) when the same external stimuli were present on all trials and trial responding was therefore controlled by events that occurred prior to the trial (“internal control”); and 2) when the external stimuli on trials on which responding was reinforced were different from the external stimuli present on trials on which responding was not reinforced (“external control”). Scopolamine impaired performance (i.e. reduced the percentage of trial responses that were reinforced) to about the same extent under the internal and external control conditions. d-Amphetamine, on the other hand, impaired nonresponding on trials only under internal control conditions. Atropine affected both internally and externally controlled non-responding but had a greater effect on internally controlled non-responding.