The associative striatum: organization of cortical projections to the dorsocentral striatum in rats.

The dorsocentral striatum (DCS) is the major site of input from medial agranular cortex (AGm) and has been implicated as an associative striatal area that is part of a cortical-subcortical circuit involved in multimodal spatial functions involving directed attention. Anterograde axonal tracing was used to investigate the spatial organization of corticostriatal projections to DCS. Injections of biotinylated dextran amine were made into several cortical areas known to project to DCS based on retrograde tracing data. These included areas AGm, lateral agranular cortex (AGl), orbital cortex, posterior parietal cortex (PPC), and visual association cortex. We discovered a previously undescribed geometry whereby the projection from AGm is prominent within DCS and the main corticostriatal projections from areas other than AGm are situated around the periphery of DCS: visual association cortex dorsomedially, PPC dorsally, AGl laterally, and orbital cortex ventrally. Each of these cortical projections is also represented by less dense aggregates of terminal labeling within DCS, organized as focal patches and more diffuse labeling. Because these cortical areas are linked by corticocortical connections, the present findings indicate that interconnected cortical areas have convergent terminal fields in the region of DCS. These findings suggest that DCS is a central associative region of the dorsal striatum characterized by a high degree of corticostriatal convergence. Copyright 2003 Wiley-Liss, Inc.