The purpose of this research study is to investigate how the brain and motor behavior changes in PD over time in response to rasagiline which is a monoamine oxidase-B(MAO-B) inhibitor. The drug rasagiline will be tested in this study as the MAO-B inhibitor. Rasagiline has been prescribed for many years to treat symptomatic Parkinson's disease. It is FDA approved for the treatment of Parkinson's disease but has not been shown to slow disease progression. The outcome and impact of this study will provide the first evaluation of MAO-B inhibitors at slowing the progression of the nigrostriatal pathway using advanced Magnetic Resonance Imaging (MRI) and functional Magnetic Resonance Imaging (fMRI) methods in PD.