Project Summary Our application addresses a fundamental need of the scientific community focused on curing Multiple Sclerosis (MS). MS is an inflammatory disease of the central nervous system that affects more than 2.5 million people worldwide with an unknown etiology. Progress in the understanding of MS has been constrained by a lack of understanding of the reciprocal interactions between behaviorally-relevant neuronal activity and changes in myelination in health and disease. The link between behaviorally-relevant neuronal activity and circuit-specific changes in myelination remain unknown, as does the role of behavior interventions in enhancing remyelination. Recently, we have developed new approaches to visualize myelin, oligodendrocytes, and their precursors in the intact mouse brain, allowing an unprecedented view into their dynamics and behavior in health and disease. In this application, we propose to capitalize on the inter-individual, longitudinal, subcellular insights revealed by these techniques to discern the effects of changes in local circuit activity and myelination on motor behavior. The objectives of this proposal are: 1) evaluate how behaviorally-relevant neuronal circuit function regulates myelination during learning and myelin repair and 2) to elucidate how changes in myelin specificity modulate motor learning and behavior. This proposal represents a novel synthesis of approaches to study neural circuit function during behavior and oligodendrocyte biology, and breaks new ground in the understanding of the mechanisms underlying motor learning and dysfunction following demyelinating injuries.