In Vivo Mapping of Fiber Pathways in the Rhesus Monkey Brain

The study of complex fiber systems in relation to the cognitive abilities of humans is a long-standing challenge for neuroscientists. With the development of diffusion tensor imaging (DTI) it is now possible to visualize large fiber bundles non-invasively. The existing knowledge of the white matter architecture largely stems from either lesion studies of human patients or, in more detail, tracer injection studies of non-human primates. Hence, it seems mandatory to com- pare DTI results with histochemical findings obtained for the same species. Using a geometrically undistorted DTI tech- nique and fiber tractography, we examined the fiber anatomy of the macaque brain in vivo and related the results to fiber pathways previously identified in monkeys with conventional tract tracing. The approach identified multiple fiber tracts including the main association and projection pathways as well as fibers of the limbic system, commissural system, optic system, and cerebellar system. In conclusion, in vivo fiber tractography based on current-state DTI allows for a compre- hensive analysis of major fiber pathways in the intact macaque brain.