The proposed projects will investigate behavioral adaptation and synaptic plasticity in the primate motor system, using a novel implantable recurrent brain-computer interface (rBCI). We will use the rBCI to create artificial corticospinal and corticocortical connections and document the effects of prolonged operation on motor behavior and strength of neural connections. The rBCI records neural activity and uses a programmable computer chip to deliver activity-contingent stimuli in real time to nervous system sites during hours of free behavior. One application is to bridge impaired biological connections, a paradigm we have demonstrated for cortically controlled electrical stimulation of paralyzed arm muscles (Moritz et al, Nature, 2008). Our proposed experiments will investigate the ability of intact monkeys to incorporate an artificial corticospinal connection into normal behavior. A second application of the rBCI is to produce Hebbian plasticity through spike-triggered stimulation, which can strengthen physiological connections (Jackson et al, Nature, 2006). Our experiments will investigate whether this plasticity can be induced with minimally invasive procedures and whether the resultant changes can be prolonged through additional interventions. Our experiments will investigate the induction of spike-timing dependent plasticity of corticospinal and intracortical neural connections and the influence of behavioral state. We will also develop a powerful multichannel rBCI to implement a wide range of transforms between recorded activity and stimulation. These studies will provide crucial evidence to inform clinical applications of this novel rBCI paradigm to more effective treatments of stroke, traumatic brain injury and spinal cord injury -- namely to use implantable computers to facilitate transmission of neural signals across lost connections and to strengthen weakened neural connections.