Deficits in response inhibition and attention in rats rendered mentally retarded by early subcortical brain damage

Young rats with lesions to either the globus pallidus, substantia nigra, median raphe, or pontine reticular formation have previously been reported to be deficient in learning a wide variety of laboratory tasks. In the current study, weanling rats subjected to one of these lesions were rested for three weeks, then examined for acquisition and extinction of a water-motivated straight alley task, and finally tested on luminous flux discriminations of increasing difficulty. All brain-damaged groups were slower than the controls in extinguishing the alley task and only the median raphe group failed to show an impairment on the discrimination problems. These results and others suggest that the foregoing lesions produce deficits in inhibitory and attentional processes. The possibility is discussed that young rats bearing these lesions might serve as a model for the investigation of the neurobiological and cognitive disturbances underlying certain classes of mental retardation in children.