Sacral nerve stimulation (SNS) is an effective treatment for refractory overactive bladder(OAB). For patient-specific and therapeutic efficacy, stimulus at levels below or above the sensory level are sometimes applied on OAB patients. Previous functional brain studies suggested that few forebrain circuits acting primarily on midbrain periacqueductal grey is responsible for facilitating voiding reflex and a sensation of voiding. The neural circuits underlying the action of SNS, and its response to different levels of stimulus is studied by functional MRI (fMRI). Differences in activation patterns resulting from subsensoy, sensory and supresensory stimulation are reported.