Motor Response to Sildenafil in PD

Sildenafil (Viagra(R))is widely used by men with Parkinsons Disease (PD) and erectile dysfunction. A number of patients have reported that when they take Sildenafil, their need of anti-PD medication is reduced. We hypotheses that sildenafil increases brain blood flow and hence improves the function of specific brain regions, improving motor function. Motor function and cerebral blood flow of 8 patients will be tested before and after Sildenafil intake and before and after anti-PD medication.