We will compare objectively measured sequence effect with a modified Purdue pegboard, a computer-based device, in de novo and advanced PD patients. The modified Purdue Pegboard will detect start and stop times for individual peg insertion and for the task in its entirety. The sequence effect in this protocol is detected by the progressive changes of time intervals per peg insertion during the testing session. A time interval is defined as the period between the start and stop times for individual peg insertion. We will conduct a placebo-controlled, four-way crossover study to determine the beneficial effect of levodopa and rTMS on the sequence effect in de novo and advanced PD. The four interventions are: levodopa and rTMS; levodopa and sham; placebo and rTMS; and placebo and sham. A replicated 4 periods and four intervention-Latin Square design will be used for the crossover design.