PROJECT SUMMARY/ABSTRACT Impaired responsiveness to external balance perturbations is a primary cause for falls and decreased mobility after stroke, limiting function and independence of stroke survivors. The neural mechanisms underlying the control and recovery of balance are poorly understood, contributing to the lack of current treatment effectiveness to prevent falls and restore mobility after stroke. There is now evidence that the cerebral cortex plays an active and important functional role in the control of human balance. The strength of neural connectivity between motor cortical regions and between the motor cortex and extremity muscles is critical to motor function and behavior. Interestingly, preliminary data from our lab showed abnormally increased interhemispheric connectivity between the lesioned and nonlesioned lower extremity motor cortical regions after stroke. Additionally, my dissertation work found that asymmetry of corticomotor connectivity to paretic and nonparetic lower limb muscles was exacerbated during muscle activity and associated with poor post-stroke walking function. However, these studies were performed during simple isolated muscle contractions in a seated position. There remains a gap in our understanding of how these cortical mechanisms contribute to the performance of critical functional tasks such as walking or balance after stroke. In this project, we propose to characterize the mechanisms of lower extremity motor control by investigating interhemispheric neural connectivity and the neural connectivity between the motor cortex and lower extremity muscles during reactive balance responses in stroke survivors using electroencephalography (EEG) and electromyography (EMG). Characterizing the neurobiological underpinnings of lower extremity motor control is critical to our understanding of mechanisms limiting balance recovery following stroke. My long-term goal is to develop better evidence-based treatment and rehabilitation strategies that target patient-specific neurophysiologic deficits, prevent falls, and maximize post-stroke functional mobility and independence. Towards my long-term goal, the overall purpose of the proposed project is to: 1) determine whether interhemispheric connectivity between the lesioned and nonlesioned primary motor cortex is abnormal during balance reactions and associated with balance function in stroke survivors and 2) evaluate if corticomuscular connectivity is abnormal during a functional balance task and associated with balance function in stroke survivors.