Somatosensory evoked magnetic fields following electric tongue stimulation using pin electrodes

Abstract

Quantitative evaluation of the sensory disturbance of the tongue is important clinically. However, because the conventional electrophysiological approach to the peripheral nerve cannot be used in the mandible owing to the deep route of the lingual nerve, we applied evoked potentials in the central nervous system. Somatosensory evoked magnetic fields (SEFs) following electric stimulation were recorded in 10 healthy subjects by means of pin electrodes placed on the tongue mucosa. Three or four components (P25m, P40m, P60m, and P80m) were identified over the contralateral hemisphere with unilateral stimulation. Because none of the components were consistently detected in all subjects, we evaluated the root mean square (RMS) of 18 channels over the contralateral hemisphere. To estimate the activated cortical response, we calculated the difference in mean RMS amplitude between 10 and 150 ms and that of the baseline period (aRMS=RMS[10, 150]-RMS[-50, -5]). The aRMS values for right-sided and left-sided stimulation were 10.18+/-7.92 and 10.99+/-8.98 fT/cm, respectively, and the mean laterality index, expressed by [(left-right)/(left+right)] was 0.025+/-0.104. This parameter can be useful for evaluating patients with unilateral sensory abnormality of the tongue.

Cortico-muscular synchronization by proprioceptive afferents from the tongue muscles during isometric tongue protrusion

“…Stimulation was applied on the right side of the tongue using an electrical stimulator (SEN-3401, Nihon Kohden, Tokyo, Japan). We used a pair of pin electrodes (400-µm diameter) with an inter-electrode distance of 3 mm for stimulation because they can safely deliver a low-intensity stimulus to a small oral region (Maezawa et al, 2008(Maezawa et al, , 2011(Maezawa et al, , 2014b. Tongue stimulation was applied 1 cm from the edge of the tongue, 3-4 cm from the tongue tip (Maezawa et al, 2014a).…”

“…However, since the initial component of tongue SEFs is sometimes hard to detect due to its small amplitude, the prominent components that occur at the middle latency with a posterior current orientation are often used as a reliable and stable parameter for tongue SEFs (Nakahara et al, 2004;Maezawa et al, 2008Maezawa et al, , 2011Maezawa et al, , 2014a. In the present study, as the mean time lag and current orientation of the low-CMC were consistent with those of middle-latency tongue SEF components, the low-CMC may reflect the cortical response of middle-latency components related to proprioception.…”

Somatosensory evoked magnetic fields following tongue and hard palate stimulation on the preferred chewing side

“…To estimate the cortical activation in each hemisphere, we used the activated 14 root-mean-square (aRMS), as was used in our previous studies [22,23]. First, we 15 calculated the spatial summation of the RMS from the 18-channel waveforms, including 16 the maximum amplitude channel over both hemispheres separately.…”

“…We 13 used a pair of pin electrodes (400-µm diameter) with an inter-electrode distance of 3 14 mm for stimulation because they can safely deliver a low intensity stimulus to a small 15 oral region [22][23][24]. The electrodes were affixed using adhesive tape.…”

“…Since none of the components was 12 detected consistently across subjects, we could not adopt them as reliable parameters for 13 assessing cortical activity. Instead, we employed the aRMS parameter following 14 previous studies [22,23], which is calculated by a 2-step analysis using spatial and 15 temporal summation. The RMS analysis is advantageous because it allows us to usedisadvantages since the RMS is affected by the distance between the head's location 1 and MEG sensors, which might differ between hemispheres.…”