U-shaped functions in a shock-escape task

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Presents results of 5 experiments with Sprague-Dawley rats. In Exp I, 136 Ss given limited training on a light-discrimination, shock-escape task (Phase 1) were divided into groups and retrained to criterion (Phase 2) from 30 min to 17 days later. A U-shaped retraining curve was obtained with best performance at 3 and 5 days. U-shaped curves were also found in Exps II-IV when the light cue was reversed for Phase 2 and when shock alone or an injection of epinephrine was given in lieu of Phase 1 training. In Exp V, an injection of physostigmine was found to improve maze performance. It is suggested that the low point of the U-shaped curve reflected a rebound period of parasympathetic dominance following a period of high sympathetic activity associated with the stress of painful shocks. (21 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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