Project Summary: This study will address the need for motivational strategies to achieve therapeutic levels of task-repetition in upper extremity rehabilitation post-stroke. To this end, we are investigating optimal strategies for utilizing music to increase motor activity, improve affect and increase functional activity in brain areas related to motor recovery post-stroke. While most empirical studies of music-based interventions utilize fixed music-playing tasks in which participants play a specified music sequence, the clinical practice of music therapy involves improvisation, allowing the music to be adjusted in the moment to reflect the emotional, social and physical needs of participants. We have therefore designed a study to characterize the effect of improvisation within music-based interventions for upper extremity rehabilitation. In Aim 1 we will characterize the motor, affective and physiological correlates of music improvisation for adults with post-stroke hemiparesis. We hypothesize that the increased improvisation will be associated with increased motor activity (measured by accelerometry) and increased affect (measured by self-report surveys following each condition and physiological arousal). In Aim 2 we will assess the neural mechanisms of music improvisation by using fMRI. We hypothesize that increased affect and motor output will be supported by increased functional connectivity between core reward, motivation and emotion-related subcortical regions and cortical motor and frontal areas. These findings will lay the foundation for optimal musi-based interventions that capitalize on improvisation to maximize motor recovery and minimize attrition rate.