Puzzle-box learning impairments in young rats with lesions to the “general learning system”

Abstract

Young rats with focal lesions to the general learning system (parietal cortex, dorsal 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 wide variety of laboratory tasks. The purpose of the current study was to determine whether weanling rats with similarly placed lesions (or frontal cortical or dorsal hippocampallesions) would subsequently manifest a learning impairment on a series of puzzle-box problems. All groups with lesions to either the subcortical components of the general learning system (GLS) or the frontal (motor) cortex were significantly impaired in overall puzzle-box learning, while the groups with parietal or hippocampal lesions were not. These data suggest that the parietal cortex should be excluded from the GLS of the rat brain.Recent studies have shown that weanling rats sustaining bilateral damage to the region of the parietal cortex, dorsal caudatoputamen, globus pallidus, ventrolateral thalamic nucleus, lateral half of the substantia nigra, ventral tegmental area of Tsai, superior colliculus, median raphe, or pontine reticular formation are deficient in learning a wide variety of laboratory tasks (Thompson, Huestis, Crinella, & Yu, 1986. These tasks include detour problems, visual and nonvisual discrimination habits, and a 3-cul maze. By virtue of the general nature of this battery of learning tests (the tests were not limited to one sense modality, to one class of laboratory problems, or to one motivational state), it has been proposed that the foregoing nine brain regions are components of the rat's general learning system (GLS). It has further been proposed that young rats bearing lesions to the GLS can be viewed as being mentally retarded, at least to the extent that one of the distinguishing features of mental retardation is a generalized learning impairment (Clarke &