DIFFERENTIAL EFFECT OF MEDIAL AND LATERAL DORSAL ROOT SECTIONS UPON SUBCORTICAL EVOKED POTENTIALS

Abstract

In different cats (2 groups of 7 each) the medial or the lateral divisions of the 7th lumbosacral dorsal root were divided while stimulating the same root distally and recording contralaterally from either the ventral thalamic nucleus or the medioventral tegmentum of the rostral midbrain. Consistently, both the blood pressure rise known to associate with avoidance of noxious stimulation and the oligosynaptic midbrain gegmental potential persisted after section of the medial division. In all animals the ventral thalamic potential persisted after severance of the lateral division. The data support Ranson''s concept of 2 functional divisions of the dorsal root, the lateral one inferentially belonging to the pain path. Other evidence suggests the existence of a path through the medioventral tegmentum which conveys impulses to be recognized as pain to more rostral levels of the nervous system.