The rat prefrontostriatal system analyzed in 3D: evidence for multiple interacting functional units.

Previous studies in monkeys disclosed a specific arrangement of corticostriatal projections. Prefrontal and premotor areas form dense projection fields surrounded by diffuse terminal areas extending outside the densely innervated region and overlapping with projections from other areas. In this study, the mode of prefrontostriatal innervation was analyzed in rats using a 3D approach. Following injections of tracers in defined cortical areas, 3D maps from individual cases were elaborated and combined into a global 3D map allowing us to define putative overlaps between projection territories. In addition to providing a detailed 3D mapping of the topographic representation of prefrontal cortical areas in the rat striatum, the results stress important similarities between the rodent and primate prefrontostriatal projections. They share the dual pattern of focal and diffuse corticostriatal projections. Moreover, besides segregated projections consistent with parallel processing, the interweaving of projection territories establishes specific patterns of overlaps spatially organized along the dorsoventral, mediolateral, and anteroposterior striatal axis. In particular, the extensive striatal projection fields from the prelimbic and anterior cingulate areas, which partly overlap the terminal fields from medial, orbital, and lateral prefrontal cortical areas, provide putative domains of convergence for integration between reward, cognitive, and motor processes.