Motor Evoked Potentials

Motor evoked potentials (MEPs) are the electrical signals recorded from the descending motor pathways or from muscles following stimulation of motor pathways within the brain. They are used for intraoperative monitoring (IOM) and neurodiagnostic testing of the motor pathways; the techniques used in these two settings differ somewhat. Muscle responses are particularly affected by anesthesia and neuromuscular blockade, and special stimulation techniques and certain anesthetic regimens are used to optimize MEPs during IOM. This article describes the neurophysiology of MEP generation and the techniques for recording and interpreting MEPs in both the intraoperative and extraoperative setting.