Transcranial magnetic-stimulation mapping of the cortical topography of the human masseter muscle

The cortical topography of several limb and trunk muscles has been disclose d using transcranial magnetic stimulation, but the corticomotor representat ion of the human jaw muscles has not yet been described. An experimental pa radigm incorporating transcranial magnetic stimulation of verified sites on the scalp was used (a) to determine the cortical topography of the human m asseter muscle and (b) to assess the reproducibility of the motor map, in s even healthy individuals. The results showed that the masseter was discrete ly represently on the motor and premotor cortex with interindividual variat ion in map areal volume and height (p < 0.05). Coefficients of variation an d reliability were low (15-18%) and high (89-96%), respectively, for motor maps obtained at experimental sessions 2 weeks apart, indicating high repro ducibility. The findings have clinical relevance in the management of patie nts with cerebral injury involving corticobulbar projections to the massete r. (C) 1998 Elsevier Science Ltd. All rights reserved.