On the direct cortical connections of the nucleus centrum medianum thalami

Abstract The center median nucleus of the cat was damaged electrolytically by a horizontally introduced electrode through the cerebellum. After a postoperative survival of ten days to a month degenerated fibers were studied by a modified Nauta method. Direct connections of the center median nucleus of diffuse character were found terminating bilaterally in V–VI layers of the neocortex. Another cortical projection from the center median nucleus terminating in layers III–IV was limited to the anterior and middle regions of the lateral and suprasylvian gyri, the anterior ectosylvian and sylvian gyri and the cornal gyrus. Fibers to the contralateral cortex were found to pass through the corpus callosum. Threshold stimulation of the center median nucleus evoked recruiting response (with a short latency) only in the limited area of the cortex whose direct connections terminate in III–IV layers. Diffuse recruiting response was obtained only with the stronger stimulation. Following lesion of the center median nucleus, diffuse recruiting response, evoked by stimulation of other nonspecific nuclei, was not obtained in the area of the cortex whose III–IV layers recieve connections from the center median nucleus. This supports the view that diffuse recruiting response during stimulation of one nonspecific nucleus is evoked by intrathalamic sprading of impulses to other nonspecific nuclei.