Motor Evoked Potentials

Abstract Motor evoked potentials can be generated by either electrical or magnetic stimulation of the corticospinal pathways. Direct activation of pyramidal cells and indirect activation of cortical interneurons generate impulses that propagate down the spinal cord as D-waves and I-waves, ultimately stimulating anterior horn cells and resulting in M-waves recorded over the targeted muscle. Transcranial electrical stimulation is most commonly employed in the operating room for intraoperative neurophysiologic monitoring, ensuring that the integrity of the motor pathways are preserved during brain or spine surgeries. The utility of transcranial magnetic stimulation has been explored in many neurologic diseases, where alterations in central motor conduction time and cortical excitability may provide important clues in diagnosis, prognosis, and monitoring response to treatment.