Architecture and connections of retrosplenial area 30 in the rhesus monkey(macaca mulatta).

Because of the sharp curvature of the retrosplenial region around the splen ium of the corpus callosum, standard coronal sections are not appropriate f or architectonic analysis of its posteroventral part. In the present study, examination of the posteroventral retrosplenial region of the rhesus monke y in sections that were orthogonal to its axis of curvature (and therefore appropriate for architectonic analysis) has permitted definition of its arc hitecture and precise extent. This analysis demonstrated that areas 29 and 30 of the retrosplenial cortex, as well as adjacent area 23 of the posterio r cingulate cortex, extend together as an arch around the splenium of the c orpus callosum and maintain their topographical relationship with one anoth er throughout their entire course. Injections of anterograde and retrograde tracers confined to retrosplenial area 30 revealed that this area has reci procal connections with adjacent areas 23, 19 and PGm, with the mid-dorsola teral part of the prefrontal cortex (areas 9, 9/46 and 46), with multimodal area TPO in the superior temporal sulcus, as well as the posterior parahip pocampal cortex, the presubiculum and the entorhinal cortex. There are also bidirectional connections with the lateroposterior thalamic nucleus, as we ll as the laterodorsal and the anteroventral limbic thalamic nuclei. The co nnectivity of area 30 suggests that it may play a role in working memory pr ocesses subserved by the mid-dorsolateral frontal cortex in interaction wit h the hippocampal system.