RecruitingDevice studyAim 3 Particle Swarm Optimization PIGDIn Parkinson's disease (PD) patients undergoing standard-of-care Deep Brain Stimulation (DBS) therapy, to compare the effect on Parkinson's symptoms of two different neurostimulator settings designed to differ from each other as much as possible with respect to how much they activate two different neuroanatomical structures: the axonal pathway from Globus Pallidus (GP) to Pedunculopontine Nucleus (PPN), and the axonal pathway from PPN to GP.