Tracking connections between striatum, and frontal and motor cortices using diffusion tensor imaging and tractography

The striatum contributes to several motor and executive functions, such as preparation for and execution of movement, and control of goal-directed and habitual behaviour. While the connections between the striatum and cortex have been extensively studied in animals, the routes and locations of the anatomical pathways in humans have been the focus of only a handful of experiments. In this thesis, the anatomical connections between the striatum (the caudate nucleus and putamen), and the frontal areas (the dorsolateral and ventrolateral prefrontal cortex) and the motor areas (the primary motor cortex, premotor cortex, supplementary motor area and presupplementary motor area) were tracked using diffusion tensor imaging (DTI) and tractography. Both the individual tracts and population maps of the connections at the group level were calculated. The found tracts held the same general shape in the different hemispheres and individuals, but the exact locations of the cortical connections and the routes of the tracts varied. This was especially notable in the tracts between the putamen and premotor cortex. All tracts at the individual level were bilaterally similar with only minor differences. The connections generally held the same shape and robustness when converted to the standard space in the group analysis, with the exception of tracts between the putamen and premotor area in both hemispheres and the tracts between the putamen and primary motor area in the right hemisphere. This thesis provides further evidence of the cortico-striatal circuits and demonstrates the power of the DTI and tractography in studying neural connections between the striatum and cortex. The routes and the locations of connections with the cortex were identified, and this information can be applied in further studies of the striatal function and connectivity, especially in tandem with TMS.