Topographic distribution of connections from the primary motor cortex to the corpus striatum in Aotus trivirgatus.

Connections between the primary motor cortex (MI) and the corpus striatum were studied in the owl monkey. Representations of specific body movements were elicited in MI by microstimulation techniques, and the efferent projections from these stimulation sites were labeled with wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP). Dense projections were found in the putamen ipsilateral to the injection site and sparser projections occupied comparable areas in the contralateral putamen. Representations of hindpaw regions projected to the dorsomedial portion of the putamen with only slight extensions across cell bridges into the caudate nucleus. Representations of the forepaw and head projected to progressively more ventrolateral zones of the dorsal two-thirds of the putamen. Projections from injections of cortex representing discrete body movements terminated in an irregular or patchy distribution over a relatively large portion of the putamen. Extensive projections from relatively discrete injections in MI are indicative of a large degree of divergence and provide evidence for possible overlap from representations of relatively disparate body parts. The results are consistent with observations reported in other species of primates, but different from those seen in carnivores. This difference is discussed with regard to possible general features of corticostriate organization. Many regions of the cerebral cortex provide afferent connections to the corpus striatum and have been shown to terminate in a topographic fashion (Kemp and Powell, '70; Yeterian and VanHoesen, '78; Selemon and GoldmanRakic, '85). In primates, the frontal, parietal, and temporal association cortices project predominantly to the caudate nucleus (Goldman and Nauta, '77; Kunzle, '78; Yeterian and VanHoesen, '78; VanHoesen et al., '81; Selemon and Goldman-Rakic, '85; Alexander et al., '86; Arikuni and Kubota, '86; Jayaraman, '87) whereas motor, premotor, supplementary motor, and somatosensory cortices project predominantnly to the putamen (Kunzle, '75, '77, '78; Jones et al., '77; Jurgens, '84; Liles and Updyke, '85; Alexander et al., '86). In general, corticostriate projections that originate in primary motor cortex are broadly distributed in the putamen and are organized in a basically topographic fashion; projections from those portions of motor cortex related to the representation of the head terminate primarily in the ventral putamen whereas the representations of the upper limb, trunk, lower limb, and tail project to successively more dorsal portions of the putamen (Kiinzle, '75, '77; Jones et al., '77). The general topographic organization of projections from primary motor cortex to the corpus striatum provides the basis for much of our understanding of functional localization in the neostriatum. This framework, however, was determined in early studies in which the sites for injection were anatomically defined according to the physiological map of Woolsey ('58). Conclusions are based on the assumption that large injections in precentral cortex involve specific body representations identical to those depicted in the same relative position of precentral cortex in previously generated summary stimulation maps (Woolsey, '58). While providing a general framework, however, it is difficult to assign a specific role to corticostriate projections in particular isolated movements when large injections, possibly involving several body representations, are utilized. Summary maps of the primate primary motor cortex have been generated in several laboratories by using contemporary