Oscillations of populations of neurons deep in the brain are thought to be responsible for some of the symptoms for Parkinson's Disease. Drugs and deep brain stimulation that re used to treat Parkinson's Disease suppress these oscillations. We have developed methods to measure how the oscillations are modulated by stimulation, to generate a phase response curve (PRC), and then use the PRC to determine optimal stimulus frequency, for open loop stimulation, and optimal phase, for closed-loop stimulation, to suppress these pathological oscillations with minimum energy.