Use of Zolpidem in Parkinson's Disease

Levodopa treatment is associated with long-term complications. Dopamine deficiency is associated with abnormal activity in certain parts of the brain. Zolpidem may change this abnormal activity and, by doing so, may work in a different way than levodopa to help parkinsonism. The working hypothesis for this aim is that ZLP is superior to placebo in acutely improving motor symptoms of PD. The investigators will conduct a randomized,controlled, double-blind, cross-over study in 40 patients with PD. Each patient will receive placebo, levodopa and 2 doses of ZLP in a randomized order on 4 different occasions, about one week apart.