SOME CONNECTIONS OF THE ORBITO-FRONTO-TEMPORAL, LIMBIC AND HIPPOCAMPAL AREAS OF MACACA MULATTA

Abstract

By means of the technic of physiol. neuronography some of the connections of the rhinencephalic and limbic areas of M. mulatta were investigated in an attempt to extend reports of previous studies. The following areas can be recognized by differences in their firing patterns trigonal, subcallosal and medial orbital, pre-callosal cingulate, supracallosal anterior cingulate, supracallosal posterior cingulate, retrospinal, posterior orbital and anterior insular, temporal polar, periamygdaloid, and entorhinal. An attempt was made to correlate these with cytoarchitectural differences and with subcortico-cortical connections whenever possible. Some of the connections of the hippocampus and amygdala were also investigated. The cortico-cortical interconnections of these areas suggest that they fall into 3 groupings. (I) The trigonal, subcallosal and medial orbital, precallosal cingulate, posterior orbital and anterior insular, temporal polar, periamygdaloid and entorhinal areas are heavily interconnected. This group may be referred to as the orbito-fronto-temporal region. (II) The 2d group includes the projection areas of the 3 divisions of the anterior thalamic nucleus. There are 3 of these areas: supracallosal anterior cingulate, posterior cingulate, and retrosplenial. According to previous studies, these areas are closely related to the cortex surrounding the cingulate sulcus and to certain aspects of the lateral surface of the hemispheres. They are functionally interconnected by extremely short fiber systems. This group may be referred to as the limbic region. (III) Finally, the consideration of the hippocampal formation as a separate region is tentative until its relation to the orbito-fronto-temporal and the limbic areas is further clarified and any possible connections with the lateral neocortex investigated.