On the development of inhibition of delay by rats of the Syracuse High- and Low-Avoidance strains.

Abstract

Male and female of the Syracuse strains received 60 trials of avoidance training in a two-way shuttlebox at 90 days of age. Approximately one month later they received additional training at the rate of 30 trials per day for 11 days (330 trials), during which acquisition of inhibition of delay was studied. Animals of the Syracuse High Avoidance (SHA/Bru) strain reached an asymptote of nearly 100% of avoidance responses (AVRs) by trial of 30 of original training, whereas those of a Low Avoidance (SLA/Bru) strain remained at nearly 0 AVRs. During subsequent extended training the SHA/Bru animals remained at 95-100% AVRs. By the end of extended training males of the SLA/Bru strain had approached 40% AVRs, the females 25% AVRs. SHA/Bru animals of both sexes showed a progressive increase in the relative frequency of long latency AVRs, indicating the development of inhibition of delay. In contrast, animals of the SLA/Bru strain, especially the males, showed a progressive increase in the relative frequency of short latency AVRs, presumably reflecting the continued acquisition of the avoidance response. These results are interpreted in terms of two-process theory of avoidance learning and in terms of the development of temporal conditioning or learning as a result of differential extinction of conditioned fear.