Movement-related magnetic fields to tongue protrusion

Movement-related magnetic fields (MRFs) associated with tongue protrusion were measured in five normal subjects using a helmet-shaped magnetoencephalography system. Bihemispherical two-dipolar patterns appeared from approximately -2000 or -1000 to 0 ms to the trigger signal indicating when protrusion of the tongue tip reached the frontal part of the palate. Equivalent current dipoles (ECDs) for the MRFs were localized on the central sulcus, 14.4 +/- 6.1 mm inferior (P < 0.0001) and 7.6 +/- 6.9 mm anterior (P < 0.01) to the ECD for the N20m in the somatosensory evoked fields for median nerve stimuli. The ECD orientations of MRFs were anterior and perpendicular to the central sulcus. These results correspond to the movement-related potentials for tongue protrusion previously recorded from subdural electrodes in patients with epilepsy. Magnetoencephalography can be applied to analyze cortical functions related to tongue movement with high resolution in time and space in normal subjects.