- The motor evoked potentials (MEPs) from the pelvic floor are obtained by sacral and transcranial magnetic stimulation using a Magstim 200 stimulator (Magstim Co., Whitland, Wales, UK). Patients are instructed to lie in the left lateral decubitus position,intra-anal sponge electrode (Dantec,Skovlund, Denmark)was lubricated and gently inserted into the anal canal.