Limbic connections of the orbital and medial prefrontal cortex in macaque monkeys.

Previous studies have shown that the orbital and medial prefrontal cortex (OMPFC) is extensively connected with medial temporal and cingulate limbic structures. In this study, the organization of these projections was defined in relation to architectonic areas within the OMPFC. All of the limbic structures were substantially connected with the following posterior and medial orbital areas: the posteromedial, medial, intermediate, and lateral agranular insular areas (Iapm, Iam, Iai, and Ial, respectively) and areas 11m, 13a, 13b, 14c and 14r. In contrast, lateral orbital areas 12o, 12m, and 12l and medial wall areas 24a,b and 32 were primarily connected with the amygdala, the temporal pole, and the cingulate cortex. Data were not obtained on the posteroventral medial wall. Three distinct projections were recognized from the basal amygdaloid nucleus: 1) The dorsal part projected to area 12l; 2) the ventromedial part projected to most areas in the posterior and medial orbital cortex except for area Iai, 12o, 13a, and 14c; and 3) the ventrolateral part projected to orbital areas 12o, Iai, 13a, 14c, and to the medial wall areas. The accessory basal and lateral amygdaloid nuclei projected most strongly to areas in the posterior and medial orbital cortex. The medial, anterior cortical, and central amygdaloid nuclei and the periamygdaloid cortex were connected with the posterior orbital areas. The projection from the hippocampus originated from the rostral subiculum and terminated in the medial orbital areas. The same region was reciprocally connected with the anteromedial nucleus of the thalamus, which received input from the rostral subiculum. The parahippocampal cortical areas (including the temporal polar, entorhinal, perirhinal, and posterior parahippocampal cortices) were primarily connected with posterior and medial orbital areas, with some projections to the dorsal part of the medial wall. The rostral cingulate cortex sent fibers to the medial wall, to the medial orbital areas, and to lateral areas 12o, 12r, and Iai. The posterior cingulate gyrus, including the caudomedial lobule, was especially strongly connected with area 11m.