Functional Connectivity of the Motor Network in Two Major Subtypes of Parkinson Disease

In this study the investigators are looking at two subtypes of Parkinson Disease (PD); "tremor-dominant" (TD) and postural imbalance and gait disorder (PIGD). This study will use magnet resonance imaging (MRI) to see how the brain reacts while resting and doing a finger-tapping task while on and off PD medication. This study will look at the differences between the two sub-types of PD and healthy volunteers. The investigators will test the hypothesis that connectivity at rest within the motor cortex and between the motor cortex and motor-associated regions such as the supplementary motor area and the pre motor cortex will not be as strong in PIGD compared to TD (increased activity and functional connectivity in TD group)