Differential effects of dorsomedial prefrontal lesions on active and passive avoidance in young and adult rats.

In Experiment I, four weanling and four adult rats had dorsomedial prefrontal lesions administered prior to initial 2-way avoidance acquisition, while in Experiment II surgical procedures for eight subjects were interpolated between acquisition and a first generalization test along CS tonal frequency. Results indicated impairment of initial avoidance acquisition following lesions, which recovered after a 30-day interval, permitting generalization testing in extinction. When DM lesions were interpolated between acquisition and testing, the effects on avoidance responding were comparatively minimal, but after 30 days lesioned subjects could not reacquire criterion avoidance levels. In all generalization tests there was little evidence of frequency control in lesioned subjects compared to eight sham operated controls of each age. Age effects in both experiments were confined to somewhat greater deficits and less recovery of responding in the pups. Two additional experiments examined passive avoidance acquisition and retention in 144 rats of 18-20, 30-32 and 100+ days of age after dorsomedial prefrontal lesions administered either prior to (Experiment III) or following (Experiment IV) initial training and testing. These data suggested rather minimal lesion effects since variability in retention was readily attributed to age differences. Data were related to prefrontal deficits that are specific to age and task requirements.