DRD2 and Parkinson disease: Although the striatum is the main input structure of the basal ganglia, receiving substantial input from the cerebral cortex, thalamus and midbrain dopaminergic neurons, and the hallmark symptoms of PD have been explained as an imbalance between Drd2 and Drd1a activity, these striatal neurons are absent from current models explaining the mechanisms of therapeutic effects in STN-DBS (Kopell et al., 2006; Montgomery and Gale, 2008).