The Effects of Midline Cerebellar rTMS on Human Pharyngeal Cortical Activity in the Intact Swallowing Motor System

We sought to compare the effects of 10 Hz cerebellar vermis (vs. unilateral hemispheric and sham) repetitive transcranial magnetic stimulation (rTMS) on cortical neuroelectrical activity and thereafter 10 Hz cerebellar vermis (vs. sham) rTMS on swallowing behaviour. Healthy participants (n = 25) were randomly allocated to receive vermis, unilateral hemisphere or sham 10 Hz cerebellar rTMS. Recordings were made using pharyngeal electromyography and manometry catheters, obtaining motor-evoked potentials (MEPs) and pressure recordings. The amplitudes of MEPs elicited using single-pulse TMS delivered to the pharyngeal areas of the motor cortex bilaterally were measured pre- and post-cerebellar stimulation. As in previous studies, abductor policis brevis (APB) MEPs were measured to assess post-rTMS modulation specificity. Swallowing was assessed using a swallowing accuracy task. Measurements were made at baseline and 15-min intervals for an hour post-intervention. Measurements involved TMS being used to elicit 10 MEPs bilaterally over the pharyngeal areas of the motor cortex, over the APB cortical representation adjacent to the pharyngeal area with the lowest resting motor threshold and 5 MEPs bilaterally over pharyngeal areas of the cerebellar hemispheres. Swallowing accuracy was assessed by giving participants 10 attempts to swallow and hit a digital target. Cerebellar vermis rTMS caused significant suppression of cortical pharyngeal MEP amplitudes compared with unilateral rTMS and sham (P = 0.0005, 0.002). APB and cerebellar MEP amplitudes were unaffected as were pharyngeal and APB MEP latencies. Following cerebellar vermis rTMS there was a significant reduction in swallowing accuracy compared with sham (P = 0.001). Our findings demonstrate cerebellar vermis rTMS exerts a suppressive effect on pharyngeal motor cortical activity and swallowing behaviour.