Reproducibility of transcranial magnetic stimulation for mapping swallowing musculature in the human motor cortex

The high incidence of dysphagia following neurologic disease, together with its impact on health, fiscal, social and quality-of-life domains, has necessitated a greater understanding of the central nervous system pathways governing swallowing function. This understanding has been assisted by the development of new technologies such as Transcranial Magnetic Stimulation (TMS). TMS represents a noninvasive means of studying swallow topography in the intact human brain. However, limited psychometric data exists to document its reliability. The aims of the present study are threefold: (1) to determine the test-retest reliability for TMS mapping of swallowing musculature; (2) to determine the topographic representation of swallowing musculature; and (3) to determine the relationship of swallow representation to handedness.;Twenty healthy adults attended 2 TMS mapping sessions, approximately 2 weeks apart. Electromyographic recordings were taken from the suprahyoid complex and the pharynx. TMS measures included: map area, map volume, optimal site location, optimal site size and motor threshold.;Results indicated that TMS was a stable measure of corticobulbar organization and excitation in this healthy cohort. Good test-retest reliability was observed for 4 TMS measures: motor map area, optimal site location-lateral coordinate, optimal site size and motor threshold (ICC: 0.76–0.98). Moderate test-retest reliability was observed for 2 TMS measures: motor map volume and optimal site location-anterior-posterior coordinate (ICC: 0.68–0.74). Swallow topography displayed a bilateral, yet clearly asymmetric, representation across all subjects. Though individual variation was noted, a groupwise lateralization to the left hemisphere was apparent across all TMS measures and for each swallow muscle studied. In addition, motor threshold was significantly lower in the left hemisphere. No relationship emerged for handedness and swallow representation.;These results provide much needed psychometric data to validate the use of TMS as an end-point measure in intervention studies overtime. Swallow topography results support a lateralization of swallow function in a normal cohort and suggest the importance of the left hemisphere for swallow function.