AN EXPERIMENTAL STUDY OF TRANSCALLOSAL CONNECTIONS BETWEEN PROREUS GYRI OF CAT

Contralateral projections of the frontal granular cortex in the cat were studied with a modified Nauta-Gygax method. Fibers arising in the gyrus proreus of one side joine the forcep minor and pass caudally toward the rostal edge of the corpus callosum. Those destined for the contralateral hemisphere turn medially and join the rostrum, while the remaining fibers take a caudal and lateral course to join the ipsilateral internation capsule. The callosal fibers continue medially through the rostrum to the contralateral hemisphere, then turn dorsally and rostally toward the frontal pole, where the most of them end in areas homotic to the lesion. A few scattered fibers are found to terminate as well in non-homotopic cortex, namely gyri cingulus, rectus and parolfactorius. We have no evidence for a callosal contribution to subcortical structures. Preterminal and terminal degeneration can be found in all cortical laminae; those subjects with short survival periods (4-5 days) exhibit a much greater density of terminal degeneration in the outer 3 layers. Transection of the dorsal aspect of the genu and rostal edge of the body of the corpus callosum results in bilateral terminal and preterminal degeneration in the anterior sylvian, ectosylvian and suprasylvian gyri. The gyrus proreus remains free of degeneration of following lesions of this type, thus confirming the observation that transcallosal axons from the gyrus proreus are confined to the rostal levels of the corpus callosum. The results are discussed with reference to the area and depth of termination of callosal axons in the cortex, and localization of connections within the corpus callosum. © 1969.