Fig. 1

Brain circuits implicated in PD bradykinesia. (a) Pathways from the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA) to the striatum and from there to the thalamic nuclei and the frontal cortex through the substantia nigra pars reticulata (SNr) and the globus pallidus internal segment (GPi). (b) Pathway from the SNc and the VTA to the striatum and from there to the brainstem through the SNr and GPi. (c) Pathway from the SNc/VTA to cortical areas such as the supplementary motor area (SMA), the parietal cortex, and the primary motor cortex (M1) and from there to the spinal cord