A. Specific Aims The proposed research will explore a new method of promoting brain reorganization and recovery of function in children with hemiplegia. Evidence shows that although the brain has remarkable reorganization after neural insult, some changes are maladaptive and leave the individual with additional loss of function. In the adult, motor neurons in the ipsilesional (stroke) hemisphere that have survived the stroke can undergo a loss of excitability. Interhemispheric (transcallosal) inhibition is imposed on these neurons from the contralesional (non-stroke) hemisphere. In both the adult and the child, evidence suggests that increased ipsilateral projections from the contralesional hemisphere to the paretic hand, likely due to compensatory behaviors, actually compound the disability. We postulate that the effectiveness of paretic limb activity training can be enhanced when combined with electrophysiologic intervention that suppresses activity in the contralesional motor neurons. Repetitive transcranial magnetic stimulation (rTMS) is a potent and noninvasive way to influence the excitability of the brain. rTMS, at low frequencies, depresses neural function. By stimulating the contralesional motor cortex at low frequency, thereby depressing its interhemispheric inhibition of the ipsilesional motor cortex, a net excitatory effect (disinhibition) is induced upon the ipsilesional motor cortex. Preceding the low-frequency rTMS with priming rTMS (see below) has been shown to increase the magnitude of the after-effect. We have recently demonstrated the safety of single treatments of 6-Hz primed low-frequency rTMS in adults with stroke and we are currently engaged in an adult NIH R01-funded study exploring the effectiveness, mechanism and safety of serial treatments of rTMS combined with motor learning training. Failure to address the large gap in pediatric brain reorganization only perpetuates the use of conservative but likely suboptimal treatment strategies. Our long-term goal is to restore excitability to surviving but dormant motor neurons in the lesioned hemisphere of children with hemiplegia and thereby promote higher motor recovery. To achieve this goal, our objective is to combine the effects of 6-Hz primed low-frequency rTMS with a current form of motor learning training, constraint induced therapy (CIT), to achieve a synergism that may yield unprecedented brain reorganization and recovery of function.