Effects of overtraining and pretrial administration of dextroamphetamine on reversal learning in rats.

Abstract

Krivanek and McGaugh (1969) have demonstrated facilitative effects of pretrial administration of amphetamine compounds on brightness discrimination in mice. These investigators suggested that the drug affected time-dependent memory-storage processes but concluded that further research was necessary to determine their nature. The effect of d-amphetamine on the ability of rats to attend selectively to specific environmental cues was examined in the present study. According to a model of discrimination learning proposed by Sutherland and Mackintosh (1971), animals receiving postcriterion training acquire a reversal shift faster than nonovertrained animals because in the former case such additional training serves to increase the probability of attending to the problem's relevant dimension. If amphetamines facilitate attentive skills, then one would expect better performance in an amphetamine-injected group on tasks requiring selective attention to particular cues than in a group not given the drug. Ss were 20 naive, adult male, Long-Evans rats randomly distributed in groups of five across four conditions: Overtrained-Saline-injected, Overtrained4-amphetamine-injected, Nonovertrained-Saline-injected, and Nonovertrained4-amphetamine-injected. All Ss were given a light gray/dark gray discrimination task in a Grice box with one irrelevant dimension (stripes). Overtrained Ss received 100 postcriterion trials while nonovertrained Ss were given the reversal shift as soon as criterion (nine consecutively correct trials) was reached. Ten minutes prior to testing, half the Ss in each of these groups received Zmg/kg of .9% saline solution, the other half receiving an equal dosage of d-amphetamine. Ten noncorrected trials were administered daily with a 3- to 5-min. intertrial interval, correct responses reinforced with 5 45-mg Noyes pellets. Results of an analysis of variance on trials to criterion showed a significant difference between the overtrained and nonovertrained groups (F = 6.70, df = 1/16, 9 < .05), thereby lending further support to the generality of the overtraining reversal effect. No significant differences were obtained, however, between the learning scores of Ss injected with saline and those injected with d-amphetamine, nor were any interactions found. The heightened task complexity in the present experiment, together with a small subject pool, may provide one explanation for the lack of facilitation found by others under similar con