Prefrontal cortical projections to the striatum in macaque monkeys: evidence for an organization related to prefrontal networks.

The organization of projections from the prefrontal cortex (PFC) to the striatum in relation to previously defined "orbital" and "medial" networks within the PFC were studied in monkeys using anterograde and retrograde tracing techniques. The results indicate that the orbital and medial networks connect to different striatal regions. The ventromedial striatum (the medial caudate nucleus, accumbens nucleus, and ventral putamen) receives input predominantly from the medial PFC (mPFC) and orbital areas 12o, Iai, and 13a, which constitute the "medial" network. More specifically, caudal medial areas 32, 25, and 14r project to the medial edge of the caudate nucleus, accumbens nucleus, and ventromedial putamen, whereas rostral areas 10o, 10m, and 11m are restricted to the medial edge of the caudate. Projections from orbital areas 12o, 13a, and Iai extend more laterally into the lateral accumbens and the ventral putamen. Area 24 gives rise to a divided pattern of projections, including fibers to the ventromedial striatum, apparently from area 24b, and fibers to the dorsolateral striatum, apparently from area 24c. Other areas of orbital cortex (11l, 12m, 12l, 13m, 13l, Ial, and Iam) that constitute the "orbital" network project primarily to the central part of the rostral striatum. This region includes the central and lateral parts of the caudate nucleus, and the ventromedial putamen, on either side of the internal capsule. The results support the subdivision of the orbital and medial PFC into "medial" and "orbital" networks and suggest that the prefrontostriatal projections reflect the functional organization of the PFC rather than topographic location.