A simple method for recording motor evoked potentials of lingual muscles to transcranial magnetic and peripheral electrical stimulation1

Abstract

Motor evoked potentials were recorded from lingual muscles by means of clip electrodes applied on the lateral side of the tongue, following transcranial magnetic stimulation and peripheral electrical stimulation of the 12th cranial nerve at the mandible jaw. Using a circular coil, the stimulation of the cerebral cortex elicited a response of about 8 ms: its amplitude was higher in the right tongue placing the coil over the contralateral hemisphere, 4 cm from the vertex, with coil currents flowing counterclockwise. Coil position and current flow direction did not significantly modify the characteristics of responses recorded from the left side. The separate stimulation of either hemisphere was better obtained using an 8-shaped coil. The latency of the motor response measured 7.7–8.0 ms, the amplitude was greater on stimulation of the contralateral than the ipsilateral hemisphere and was larger recording from the right (3.3±1.1 mV) than from the left (1.2±0.7 mV) side.

Positioning the circular coil over the parieto-occipital skull, a response of 4.1±0 3 ms was obtained, reflecting the intracranial activation of the hypoglossal nerve. The peripheral stimulation at the mandible elicited a response of 3.2±0.5 ms. The method described appears simple and reliable, potentially helpful in clinical practice.