Visual and auditory delayed discriminations in male and female Wistar rats

Abstract

Different groups of male and female Wistar rats were exposed to a discrete-trial delayed discrimination procedure, in which subjects were required to discriminate between a continuously or intermittently presented visual (half of the subjects) or auditory (other half of the subjects) stimulus. The opportunity to respond was delayed for 0, 5, 10 or 20 s after stimulus presentation. Both response levers were inserted into the experimental chamber immediately upon the termination of the delay interval. A press on the left lever was followed by food if the continuous stimulus had been presented, while food was presented following a press on the right lever if the intermittent stimulus had been presented. During sessions 1–60, each incorrect response or failure to respond during the 5-s lever presentation was followed by presentation of the same visual or auditory stimulus, and the same delay interval, once the intertrial interval was terminated. This sequence was repeated until a correct response occurred. During sessions 61–90, repeated presentations of the same trial following incorrect responses or a failure to respond on initial trials were no longer presented. All other experimental contingencies remained unchanged. Response accuracy increased with prolonged training. Subjects exposed to the visual delayed discrimination procedure showed less accurate performance than subjects who were exposed to the auditory delayed discrimination procedure. Response accuracy was higher when the delay interval was short than when it was long. Males made more correct responses than females. However, significant sex by delay interval duration interaction effects were not observed, suggesting that sex differences in response accuracy cannot be attributed to sex differences in memory, but may rather result from sex differences in other, non-mnemonic processes.