Changes in the perioral muscle responses to cortical TMS induced by decrease of sensory input and electrical stimulation to lower facial region

Objective: To determine the changes in the motor cortex due to repetitive electrical stimulation and cutaneous anesthesia in lower facial region. Methods: A total of 11 subjects participated in the study of repetitive electrical stimulation, and 10 other subjects in the study of lower facial anesthesia. Facial nerve root and face associated cortical MEPs by transcranial magnetic stimulation (eight-shaped coil) were recorded from perioral muscles pre- and post- electrical stimulation and lower facial anesthesia. Cheek near to the corner of the mouth was transcutaneously stimulated by bipolar surface electrode giving repetitive electrical shocks at 5 Hz. Five percent lidocain/prilocain local anesthetic cream was applied to left or right lip-cheek region. Results: There was no significant change in perioral MEP responses after 10–30 min of 5 Hz electrical stimulation. We found a significant increase of amplitude in cortical MEP recordings during lower facial anesthesia especially in cases of cortical magnetic stimulations ipsilateral and contralateral to the anaesthetized side and in perioral recordings contralateral to the anaesthetized side. Conclusions: The present study demonstrates that topical anesthesia to the lower facial region leads to cortical modulation and fast plastic changes in both hemispheres that are directed to the normal side.