The effects of delay interval, intertriai interval, amnestic drugs, and differential outcomes on matching-to-position in rats

Abstract

A matching-to-position task was used to investigate the effects of numerous variables on spatial working memory in the rat. The primary interest was whether implementing the differential outcomes procedure (DOP), which correlates specific reinforcers with specific discriminative stimuli, would enhance memory performance under a variety of conditions (long delay intervals, short intertrial-intervals [ITIs], amnestic drugs). When working memory was taxed, either by excessive delay intervals or very short ITIs, the DOP did enhance performance. Scopolamine disrupted performance in a delay-dependent manner, regardless of either reinforcement or ITI condition; however, performance was worse in the group that was trained with nondifferential reinforcement. MK-801 also impaired performance, but the effect was different from that obtained with scopolamine. First, the effect of MK-801 was delay independent; second, the greatest disruption of performance was in the group of rats trained with differential reinforcement. These data suggest that scopolamine and MK-801 impair memory performance in very different ways, depending on the nature of the task.