Project Summary Closed-loop VNS was recently approved by the FDA to restore upper limb mobility for patients with stroke. Moreover, preclinical and early clinical studies suggest that closed-loop VNS improves recovery from conditions such as spinal cord injury, traumatic brain injury, post-traumatic stress disorder and addiction. Despite the wide- ranging etiology of these conditions, the therapeutic model is similar; VNS is paired with a relevant rehabilitation protocol. The precise timing of stimulation is a key element to drive specific circuit plasticity and functional recovery. Yet, VNS activates widespread brain networks, raising the question of how closed-loop VNS can lead to circuit-specific alterations in plasticity and functional recovery. The goal of this proposal is to identify the mechanism by which closed-loop VNS drives circuit-specific plasticity during motor learning and stroke recovery. Our lab has shown, for the first time, that VNS elicits phasic cholinergic signaling from the basal forebrain (BF) and modulates inhibitory interneurons in motor cortex. Cholinergic signaling from BF is recognized to play a critical role in learning and plasticity and recovery from injury. The influence of cholinergic signaling on cortical plasticity is mediated through inhibitory interneurons, which gate synaptic plasticity within cortex. We hypothesize that closed-loop VNS drives recovery from stroke through cholinergic modulation of inhibitory interneurons to produce circuit-specific plasticity. The objectives of this proposal will be 1) to determine if closed-loop VNS drives synaptic plasticity on active circuits via cholinergic signaling; 2) to determine the influence of cholinergic signaling on inhibitory interneuron gating of synaptic plasticity and; 3) to explore the role of cholinergic activity and inhibitory interneuron gating of plasticity during stroke recovery. This data will provide a detailed mechanism by which closed-loop VNS can drive plasticity in the healthy and injured nervous system.