Working memory in young rats with lesions to the “general learning system”

Abstract

Young rats with certain lesions to the caudatoputamen, globus pallidus, ventrolateral thalamus, substantia nigra, ventral tegmental area, superior colliculus, median raphe, or pontine reticular formation have previously been reported to be deficient in learning a broad range of laboratory tasks. The purpose of the current study was to determine whether young rats with similarly placed lesions (or with dorsal hippocampal lesions) would manifest a working-memory deficit on a variant of a spatial delayed-response task, and whether the degree of any such impairment would correlate with an independent assessment of learning ability (as gauged by performance on a visual-discrimination habit and a series of detour problem-solving tasks). Although all nine brain-damaged groups were inferior to sham-operated controls in acquiring the discrimination and detour problems, only six groups (those with lesions to the caudatoputamen, ventrolateral thalamus, ventral tegmental area, median raphe, pontine reticular formation, and dorsal hippocampus) were significantly impaired in their performance of the working-memory task. All correlations between the various performance scores were positive, but none exceeded.32. These results, together with others obtained from rats with similarly placed subcortical lesions, are discussed in terms of certain cognitive theories of intelligence and mental retardation.