Figure 2: Hypothetical alterations of the basal ganglia-thalamo-cortical motor circuit. The striatum receives input from the primary somatosensory area (PSA) and from other motor and sensory cortex. The striatum projects by direct and indirect pathways to the major output structures of the basal ganglia, the globus pallidus interna (GPi) and substantia nigra reticulate (SNr). An indirect pathway includes a striatal-globus pallidus externa (GPe) projection. Some GPe fibers project to the subthalamic nucleus (STN) and GPi/SNr, and other fibers project directly to the GPi/SNr. The GPi/SNr, which in turn, projects to the thalamus with a subsequent feedback to motor cortex, primarily the SMA. The effect of each structure on subsequent structures is to increase (+) or decrease (-) neuronal activity as indicated, adapted from Tempel et al. [15] and Garfen [22]. In dystonia patients, since glucose hypermetabolism in the basal ganglia, thalamus, and PSA was observed, it is surmised that the whole of the loop is being activated.