Associational projections of the anterior midline cortex in the rat: intracingulate and retrosplenial connections

Past studies indicate that distinct areas of anterior midline cortex in the rat contribute to diverse functions, such as autonomic nervous system regu lation and learning, but the anatomical substrate for these functions has n ot been fully elucidated. The present study characterizes the associational connections within the midline cortex of the rat by using the anterograde transport of Phaseolus vulgaris leucoagglutinin and Fluororuby. The prelimb ic area and the rostral part of the anterior cingulate area (both dorsal an d ventral subdivisions) are extensively interconnected with each other. In addition, the caudal half of anterior cingulate cortex has extensive projec tions to precentral medial cortex and caudally directed projections to retr osplenial cortex. Other cortical areas within anterior midline cortex have relatively limited cortical-cortical projections. The infralimbic, dorsal p eduncular, and medial precentral cortices have dense intrinsic projections, but have either very limited or no projections to other areas in the anter ior midline cortex. Although it has been suggested that cortical-cortical p rojections from anterior cingulate cortex and prelimbic cortex to infralimb ic cortex may be important for linking learning processes with an autonomic nervous system response, the paucity of direct projections between these a reas calls this hypothesis into question. Conversely, the results suggest t hat the anterior midline cortex contains two regions that are functionally and connectionally distinct. (C) 1999 Elsevier Science B.V. All rights rese rved.