A method, apparatus, and system for treating patients suffering from movement disorders having the ability to determine one or more biomarkers indicative of a disease state. In some embodiments, the biomarker may be used as a closed-loop feedback signal to control the delivery of therapy (such as electrical stimulation or drug therapy), and which may also be used as an indication of therapy effectiveness. One embodiment uses electrodes placed in the brain to measure EEG or local field potential (LFP) signals, from which the one or more biomarkers may be determined.