Effect of repetitive transcranial magnetic stimulation on altered perception of One’s own face

Abstract

Background: Chronic orofacial pain (COP) patients often perceive the painful face area as "swollen" without clinical signs; such self-reported illusions of the face are termed perceptual distortion (PD). The pathophysiological mechanisms underlying PD remain elusive. Objective: To test the neuromodulatory effect of repetitive transcranial magnetic stimulation (rTMS) on PD in healthy individuals, to gain insight into the cortical mechanisms underlying PD. Methods: PD was induced experimentally by injections of local anesthetic (LA) around the infraorbital nerve and measured as perceived size changes of the affected area. Participants were randomly allocated to inhibitory rTMS (n ¼ 26) or sham rTMS (n ¼ 26) group. The participants rated PD at baseline, 6 min after LA, immediately, 20 and 40 min after rTMS. The rTMS (inhibitory and sham) was applied to face (lip) representation area of primary somatosensory cortex (SI) as an intervention at 10 min after the LA, when the magnitude of PD is large. As inhibitory rTMS, continuous theta-burst stimulation paradigm (50 Hz) for 40s was employed to inhibit cortical activity. Results: We demonstrated a significant decrease in the magnitude of PD immediately and 20 min after the application of inhibitory rTMS compared with sham rTMS (P < 0.006). In two control experiments, we also showed that peripheral muscle stimulation and stimulation of a cortical region other than the lip representation area had no effect on the magnitude of the PD. Conclusions: Inhibitory rTMS applied to a somatotopical-relevant cortical region modulates PD of the face in healthy individuals and could potentially have therapeutic implications for COP patients.

Conditioning to Enhance the Effects of Repetitive Transcranial Magnetic Stimulation on Experimental Pain in Healthy Volunteers

“…Indeed, a single session study with similar rTMS parameters and design to the present study showed that active rTMS over both M1 and DLPFC similarly increased thermal pain thresholds (heat and cold) among healthy volunteers, suggesting comparable effects of DLPFC and M1 when compared to sham ( 24 ). In addition, there is also evidence showing analgesic and sensory modulatory effects of rTMS when applied to the primary or secondary somatosensory cortex (S1 and S2 respectively) ( 88 , 89 ). In fact, one study favored rTMS stimulations over S2 relative to M1, DLPFC and sham in order to increase heat pain thresholds ( 90 ).…”

Impact of oral motor task training on corticomotor pathways and diadochokinetic rates in young healthy participants

“…20,28 In order to locate the lip representation of the corticomotor area, one electrode is attached to the right corner of the upper lip and another to the right corner of the lower lip, with MEPs being recorded in the orbicularis oris, starting from a site 3 cm lateral and 1.5 cm anterior to the FDI representation, along a straight line towards the corner of the left eye. 18,19 For tongue MEP recording, electrodes were placed on the right side of the dorsal surface of the tongue (2-3 mm from the midline, 10 mm from the tongue tip) with an interelectrode distance of 2 cm. 6 MEPs were evoked by stimulation of discrete areas of the left scalp, approximately 2-3 cm anterior to the Cz and 7-8 cm lateral to the midsagittal plane.…”

“…It was defined as the minimum stimulus intensity that produced 5 out of 10 discrete MEPs for each target muscle with peak-to-peak amplitude (i.e., greater than or equal to 10 μV for the tongue, lip, and masseter and 50 μV for the FDI) considering background EMG activity clearly discernible on the monitor from 12 consecutive stimuli. 6,18,20,26 The peak-to-peak amplitudes of the MEPs (μV) were used to assess corticomotor stimulusresponse (S-R) curves and map the motor cortex for sites from which the MEPs could be evoked. S-R curves were constructed in steps of motor threshold, from −10%, +20% to +60% (i.e., respectively at 90%, 100%, 120%, and 160% motor threshold), in a randomised order, where the motor threshold was the resting or active motor threshold measured at the specific time of creating the S-R curve.…”

“…Few studies have demonstrated changes in corticomotor pathways representing the lips, 18,19 tongue, and jaw muscles after OMT 4–7,20 . However, no studies have addressed the modulation‐associated plasticity and lip, masseter, and tongue motor representations in the human motor cortex and oral DDK rate after Pa, Ta, and Ka single syllable repetition.…”

“…[14][15][16] The PaTaKaRa™ app is a modern, innovative, and reproducible method for checking oral frailty status and improving the oral function using a series of single syllables (i.e., Pa, Ta, and Ka) pronounced as rapidly as possible. 17 Few studies have demonstrated changes in corticomotor pathways representing the lips, 18,19 tongue, and jaw muscles after OMT. [4][5][6][7]20 However, no studies have addressed the modulationassociated plasticity and lip, masseter, and tongue motor representations in the human motor cortex and oral DDK rate after Pa, Ta, and Ka single syllable repetition.…”