This is a collaboration between experts at UCSD, UCLA, UCSF, UC Irvine, and UC Davis to examine plasticity and regeneration in the non-human primate spinal cord. Our goal is to enhance knowledge and translational relevance of research on spinal cord injury (SCI). Given findings of the last 5 years in this model, we focus this renewal on efforts to better understand and amplify the endogenous plasticity revealed in the primate system, and to test the translation of leading potential treatments discovered in non-primate models. Aim 1: Examine Electrophysiological and Anatomical Mechanisms Underlying Spontaneous Forelimb Functional Improvement After Primate SCI. Like humans, monkeys exhibit spontaneous improvement (but not full recovery) after C7 hemisection, and we have identified a remarkable degree of spontaneous sprouting of the primate corticospinal projection in association with this functional improvement. Aim 1 will examine the time course of molecular, electrophysiological and systems-level (both corticospinal and non-corticospinal) mechanisms associated with behavioral improvement. Aims 2 and 3: Test Candidate Therapies for Promoting Recovery The primate model of SCI is important not only for testing the efficacy of therapies discovered in rodents, but also for developing methods to deliver potential treatments to the larger primate system. We have tested several therapies in the last period of this grant, and plan to focus on new, promising approaches in the current grant period that target enhancement of plasticity and recovery. We will use the same techniques as in Aim 1 to examine the functional, electrophysiological, and anatomical consequences of the following: Aim 2: Chronic, Intermittent Stimulation with Cortically-Implanted Electrodes to Drive Plasticity of Spared Corticospinal Projections and Intraspinal Circuits. Aim 3: Chase Treatment after SCI.