Parkinson's disease (PD) is a common, debilitating neurological disease that causes movement deficits. Drug treatments are effective initially but cause unwanted side-effects in many patients. Electrical stimulation of the brain is an adjunct treatment, but current methods can also cause side-effects. Our goal is to improve treatment options for patients by identifying a new brain target and stimulation protocol combination that restores movements with minimal side-effects. In PD, normal movement generation is blocked by abnormal activity patterns in the brain movement control circuit. We aim to bypass this block by providing normal patterns of activity, initially using electrical stimulation. To elucidate the mechanism of brain stimulation for the treatment of PD, we will also use new optogenetic technology that enables light to activate very specific types of brain cells. This new technology may one day replace the use of electrical stimulation to treat PD.