Lemniscal and extralemniscal thalamic lesions and tactile discrimination in the rat.

Abstract

Rats with lesions centered in the ventrobasal nuclear complex, the parafascicular-centrum median complex, or the posterior nuclear group were compared to each other and to control groups with and without thalamic damage on a battery of five two-choice tactile discriminations. Almost all animals mastered the first four discriminations, although many rats with lesions did not learn the discrimination with the least difference between positive and negative stimuli. Statistical analyses revealed differences in the raw scores and in the frequency of “deviant” scores between animals with lesions of the ventrobasal complex and controls, as well as between rats with parafascicular damage and controls. Animals with damage in the posterior nuclear group also showed some deficits on the problems. Histological analyses revealed possible differences in lesion size and locus for ventrobasal and parafascicular animals that did and did not master the series of tactile discriminations. Results are interpreted in terms of the roles of lemniscal and extralemniscal systems in somatic sensation and performance.