Bilateral Changes in Cortical Motor Representation of the Tongue after Unilateral Peripheral Facial Paralysis: Evidence from Transcranial Magnetic Stimulation

Abstract

Motor evoked potentials of the lingual muscles due to focal cortical transcranial magnetic stimulation were investigated in 5 patients with unilateral total facial paralysis with regard to amplitude as a function of the coil position on the interaural line. Maximum bilateral responses could be obtained at mean stimulus positions of about 6 to 8 cm lateral to the vertex. In comparison with healthy subjects, the patient group had significantly smaller mediolateral calculated centers for ipsilateral and contralateral responses. At the optimum stimulus positions, the patients' mean motor evoked potential amplitudes were significantly lower than those in healthy subjects. These alterations could be observed on both cortical hemispheres, but were more pronounced for the hemisphere contralateral to the side of facial paralysis. Thus, we provide strong evidence of bilateral changes in lingual cortical motor representation following facial paralysis with an invasion of the facial motor area by the tongue motor representation.