Project Summary Electrical microstimulation has become a mainstay of fundamental neuroscience exploration and an increasingly prevalent clinical therapy. Despite the growing prevalence of neuromodulation therapies, the fundamental physiological and mechanistic properties driving the beneficial effect for the patient are poorly understood. This R01 application aims to greatly improve our understanding of how different non-neuronal cells (myeloid lineage, oligodendrocyte progenitor lineage, and vascular smooth muscle cells) respond and contribute to the electrical stimulation response. Understanding of the relationship between stimulation parameters and supporting non-neuronal cell activity, including blood flow, will help determine the impact of electrical microstimulation on chronic circuit behavior in-vivo over time. In this proposal, we use leading-edge in vivo multiphoton imaging techniques with multiple transgenic animals to systematically evaluate the relationship between stimulation parameters and the induced changes over time at the molecular, cellular, and local network. An improved understanding of the impact of electrical microstimulation on the overall tissue health, changes to the foreign body response, stimulation of tissue repair, and safety limits will help inform improved stimulation paradigms and device design for therapeutic applications and basic neuroscience research.