IMPROVED REPRODUCIBILITY OF MAGNETIC STIMULATION-EVOKED MOTOR POTENTIALS IN THE HUMAN MASSETER BY A NEW METHOD FOR LOCATING STIMULATION SITES ON THE SCALP

In magnetic-stimulation studies where motor-evoked potentials (MEP) ar e measured on different occasions, accurate relocation of the stimulat ion site on the scalp is essential. Here a novel method of locating ne ural stimulation sites was tested and the reproducibility of MEPs in t he human masseter assessed. The heads of the participants were immobil ized in a plastic mask that incorporated a grid overlying the left cer ebral hemisphere. A figure-of-eight coil was oriented with a micromani pulator. Electrodes were placed over the right masseter using a standa rdized method. Two discrete sites on the grid were stimulated alternat ely at threshold + 10% whilst participants clenched their teeth. Recor dings were repeated after the mask and electrodes hap been removed and replaced. Within individual participants, the latency and amplitude o f the MEP were reproducible between trials and when the mask and elect rodes were replaced. The new method appears to be accurate and practic al when recording longitudinal MEP data in the masseter. (C) 1998 Else vier Science Ltd. All rights reserved.