The effects of differential outcomes on learning and memory in young and aged rats

It is claimed that using a differential outcomes procedure (DOP) generally results in (1) a faster acquisition of discrimination and (2) less disruption in accuracy when a delay interval is inserted between the stimulus cue and the opportunity to respond; this effect is best known as the differential outcomes effect (DOE). The DOE has been especially evident in aged participants. However, when acquisition in a matching-to-position task under DOP was compared to that under a non-differential outcomes procedure (NDO) by Savage, Pitkin, and Careri (1999), no difference in rate of acquisition was found between young and old rats. In the present experiment, we evaluated the effect of using a differential outcomes procedure on both learning and memory in young (3 months) and aged (24 months) rats in a more standard two-choice stimulus discrimination task. The results reported in this article showed in both young and aged subjects that DOP led to faster acquisition and less disruption in the percentage of correct responses as the delay interval was lengthened. These results confirm that employing DOP is an effective training strategy that can increase speed of acquisition and enhance memory in both young and aged subjects, with larger effects being seen in older rats.