Although most research in PD has a focus on presynaptic dopaminergic denervation, new lessons may be learned by exploring to what extent alterations in non-motor and non-dopaminergic systems may play a role in the balance impairment in this disorder. This project is designed to evaluate striatal pre-synaptic dopaminergic, cortical, thalamic, and brainstem cholinergic, cognitive, and oculomotor mechanisms underlying the risk of falling and imbalance in PD. The proposed study will exploit advances in our center in the development of dynamic biomathematical modeling of electronic platform data, application of specialized cognitive and oculomotor assessments, and positron emission tomography (PET). This novel multi-system approach holds promise for understanding mechanisms of falling in PD beyond pre-synaptic dopaminergic nigrostriatal denervation.