Deep-brain electrical stimulation (DBS) can provide substantial motor benefit and impact non-motor domains of cognition and mood in Parkinson disease (PD) when implanted in the subthalamic nucleus (STN). However, the neural mechanisms underlying these effects are not fully understood. We have applied functional neuroimaging, manipulation of DBS parameters and behavioral tests to these questions. This work has been funded by NINDS (Mapping Mood in the Subthalamic Nucleus; NS058797) and collaborators include Joel Perlmutter, Kevin Black and Sarah Eisenstein. Recently we have begun to collaborate with the Culver Lab to apply high density diffuse optical tomography (HD-DOT) to the questions of how STN DBS alters functional networks in the brain.