Unilateral suppression of pharyngeal motor cortex to repetitive transcranial magnetic stimulation reveals functional asymmetry in the hemispheric projections to human swallowing
Source: The Journal of Physiology, Volume 585, Number 2, December 2007 , pp. 525-538(14)
Abstract:Inhibitory patterns of repetitive transcranial magnetic stimulation (rTMS) were applied to pharyngeal motor cortex in order to establish its role in modulating swallowing activity and provide evidence for functionally relevant hemispheric asymmetry. Healthy volunteers underwent single pulse TMS before and for 60 min after differing intensities of 1 Hz rTMS (n= 9, 6 male, 3 female, mean age 34 ± 3 years) or theta burst stimulation (TBS) (n= 9, 6 male, 3 female, mean age 37 ± 4 years). Electromyographic responses recorded from pharynx and hand were used as a measure of cortico-motor pathway excitability. Swallowing behaviour was then examined with a reaction time protocol, before and for up to 60 min after the most effective inhibitory protocol (1 Hz) applied to each hemisphere. Interventions were conducted on separate days and compared to sham using ANOVA. Only high intensity 1 Hz rTMS consistently suppressed pharyngeal motor cortex immediately and for up to 45 min (−34 ± 7%, P≤ 0.001). Adjacent hand and contralateral pharyngeal motor cortex showed no change in response (−15 ± 12%, P= 0.14 and 15 ± 12%, P= 0.45, respectively). When used to unilaterally disrupt each hemisphere, rTMS to pharyngeal motor cortex with the stronger responses altered normal (−12 ± 3%, P≤ 0.001) and fast (−9 ± 4%, P≤ 0.009) swallow times, not seen following rTMS to the contralateral cortex or after sham. Thus, suppression of pharyngeal motor cortex to rTMS is intensity and frequency dependent, which when applied to each hemisphere reveals functionally relevant asymmetry in the motor control of human swallowing.
Document Type: Research article
Affiliations: 1: University of Manchester, Department of Gastrointestinal Sciences, Hope Hospital, Salford M6 8HD, UK 2: Department of Physiology, Rouen University Hospital, 1 rue de Germont, 76031 Rouen and UPRES EA 3830 IFRMP 23, GRHV Research Group, Rouen University, Rouen, France 3: Institute of Neurology, Sobell Department of Motor Neuroscience and Movement Disorders, Queen Square, London WC1N 3BG, UK
Publication date: 2007-12-01