Somatosensory-evoked magnetic fields following stimulation of the tongue in humans

Objective To clarify the characteristics relating to the temporal dynamics of the tongue primary somatosensory cortex (SI). Methods We fabricated individual intraoral devices and recorded somatosensory-evoked magnetic fields (SEFs) from 10 normal subjects. The tongue was stimulated with a concentrated bipolar electrode in four areas: the right and left antero-lateral margins, and the right and left postero-lateral margins. Results The primary component was recorded about 19 ms post-stimulation. Six components, termed 1M, 2M, 3M, 4M, 5M, and 6M, respectively, were found within 130 ms of the stimulation. These activities were detected in hemispheres both contralateral and ipsilateral to the stimulation, and were estimated to be located around the tongue SI. In addition, the latency of the contralateral hemisphere was significantly shorter than that of the ipsilateral hemisphere for all components, independent of the area stimulated. Conclusions Tactile stimulation of the tongue-elicited activity in the tongue SI in both hemispheres. Significance This is the first study to investigate the brain responses evoked by stimulating different areas of the tongue, using magnetoencephalography