Twenty-four PD patients (n=24) will be randomly assigned to receive one of two interventions for a duration of two weeks. In Group 1, subjects will participate in daily sessions of sham-rTMS followed by supervised aerobic exercise (Sham rTMS+Aerobic); in Group 2, subjects will participate in a combination of rTMS and supervised aerobic exercise (Real rTMS+Aerobic). Serum BDNF-TrkB signaling in lymphocytes and TMS-based electrophysiological measures of LTP-like plasticity will be measured. A comparison of such measures in a group of patients with PD and in a group of age-matched controls (n=12) will be analyzed to establish the effect of the disease on indices of plasticity.