A conditioned reflex study of sensory defects caused by cortical somatosensory ablations

Abstract

Abstract The learning and retention of an instrumental alimentary conditioned reflex elicited from either hindlimb by reproducible, light tactile stimuli (puffs of air) was studied in relation to the selective removal of the electrophysiologically determined hindlimb portions of cortical areas S I and S II. Ablations were made in one hemisphere at a time. No difference between the sides was observed in the postoperative learning of dogs with unilateral ablations. In preoperatively trained dogs the ablations resulted in transient impairment mainly of the reflexes from the contralateral limb. Ablations were made in the second hemisphere of the preoperatively trained dogs after recovery from the initial ablations and in the second hemisphere of one postoperatively trained dog after complete learning. These ablations also gave transient impairment mainly of the reflexes from the limb contralateral to the latest ablations. The effects of the second ablation were always more severe than those of the initial ablation. None of the effects could be attributed to changes in the motor performance of the conditioned reflex. It is postulated that the removed parts of the somatosensory areas were engaged in the transmission of the sensory impulses en route to elicit the reflex response, either directly as part of the reflex pathway or indirectly through exerting facilitation on the reflex pathway at a distance. The observed contra-and ipsilateral impairments are discussed with regard to quantity and quality in relation to previous studies.