Striatal projections from the rat lateral posterior thalamic nucleus.

The dorsocentral striatum (DCS) has been implicated as an associative striatal area receiving inputs from several cortical areas including medial agranular cortex (AGm), posterior parietal cortex (PPC), and visual association cortex to form a cortical-subcortical circuit involved in directed attention and neglect. The lateral posterior thalamic nucleus (LP) may also play a role in directed attention and neglect because LP has robust reciprocal connections with these cortical areas and projects to DCS. We used anterograde axonal tracing to map thalamostriatal projections from LP and surrounding thalamic nuclei, with a focus on projections to DCS. The thalamic nuclei investigated included LP, laterodorsal thalamic nucleus (LD), central lateral nucleus (CL), and posterior thalamic nucleus (Po). We found that the mediorostral part of LP (LPMR) projects strongly to DCS as well as to the dorsal peripheral region of the striatum. Further, there is topography within LPMR and DCS such that the far medial LPMR projects to the central region of DCS (projection area of AGm) and the central LPMR projects to the dorsal region of DCS (projection area of PPC and Oc2M). In contrast, the laterorostral part of LP (LPLR) and other thalamic nuclei surrounding LP project to dorsolateral to dorsomedial peripheral regions of the striatum but do not project to DCS. These findings indicate that DCS is a region of convergence for thalamostriatal and corticostriatal projections from regions that are themselves interconnected, serving as the key element of the corticostriatal-thalamic network mediating spatial processing and directed attention.