We hypothesize that use of the affected arm associated with decreased use of the unaffected arm are useful triggers of plasticity and reacquisition of motor function after stroke. We expect to identify cortical and subcortical regions newly activated in each patient after reacquisition of use of the affected arm, understand the coherence and timing of activation of new brain regions recruited and quantify plastic changes in motor representation areas targeting arm muscles in the affected and unaffected arm.