NEURONOGRAPHIC ANALYSIS OF MEDIAL AND BASAL CEREBRAL CORTEX. II. MONKEY

Abstract

The method of strychnine neuronography was used to explore the interconnections between the limbic and extralimbic cortex of the medial and basal aspects of the cerebral hemispheres. Large regional systems can be discerned on the basis of reciprocal connections of all points within such a region. Limits of the region are demarcated by lack of or by unidirectional connections. 6 regional systems were described. (1) frontotemporal: the classification of this region is based on a firing pattern common to the strychninization of the posterior orbital, anterior insular, temporal polar and pyriform (periamygdaloid) areas. New findings include the demonstration of the firing pattern of the anterior insula as well as the reciprocal connections of the posterior orbital and insular cortex with the frontal operculum. (2) Medial occipitotemporal: this region is characterized by the firing pattern common to the strychninization of the cortex of the hippocampal gyrus and portions of the fusiform and lingual gyri. New findings are 2-way connections relating the limbic areas of the medial temporal cortex to a variable extent of medial occipital and medial temporal extralimbic cortex. (3) Medial parieto-occipital: this region is delineated by the firing pattern common to the strychninization of the limbic cortex of the posterior cingulate and parasplenial gyri and the contiguous extralimbic cortex of the precuneus. Its connections with the hippocampus have been descr. (4) Medial frontoparietal: this regional classification is based on the firing pattern common to the strychninization of the rostral cingulate gyrus (limbic cortex) and the superior frontal area (extralimbic cortex). The extent of firing of the medial cortex from the superior frontal area is surprising and has not been previously reported. (5) Medial frontal: this region is delineated by the firing pattern common to the strychninization of the limbic cortex of the subcallosal and medial orbital areas, and the extralimbic cortex of the ventromedial frontal polar area. The demonstration of interconnections among these areas has not previously been reported. (6) Hippocampus: although no reciprocal connections between hippocampus and the other regions were established, the unidirectional firing of these regions into Ammon''s formation is of interest. The anterior hippocampus is fired by the posterior orbital, anterior insular, and temporal polar and pyriform (periamygdaloid) areas. The posterior hippocampus is fired by the cortex of the hippocampal gyrus and the parasplenial and posterior cingulate areas.