Delayed spatial response alternation: effects of delay-interval duration and lesions of the medial prefrontal cortex on response accuracy of male and female Wistar rats.

A delayed spatial response alternation procedure was used to assess behavioural differences between male and female Wistar rats, assumed to involve memory functioning. In Expt. I, subjects were required to alternate responses between two levers in an operant environment. The delay between response opportunities was varied between 1, 3, 7.5 and 15 s in different experimental conditions. Incorrect responses produced a time-out from experimental contingencies for the duration of the currently active delay interval. Response accuracy decreased for males as well as females as the duration of the delay interval was increased. Performance improved as subjects were exposed to the different delay interval durations during consecutive trials. Sex differences in behavioural accuracy were not observed. In Expt. II, some subjects who participated in Expt. I received lesions of the medial prefrontal cortex, while others were control-operated. When re-exposed to the 1 and 7.5 s delay conditions of the first experiment, lesioned subjects at first behaved less accurately than control-operated subjects. Accuracy, however, improved after prolonged exposure to the experimental conditions. Sex differences in behaviour after surgery could not be observed.