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

Abstract

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.

The Immediate Effects of Intermittent Theta Burst Stimulation of the Cerebellar Vermis on Cerebral Cortical Excitability During a Balance Task in Healthy Individuals: A Pilot Study

“…Additionally, a study demonstrated that cTBS stimulating cerebellar vermis could lead to a significant influence on balance function as body sway increases ( Colnaghi et al, 2017 ). For other effects on humans, Sasegbon et al (2021) found that TMS on cerebellar vermis has an inhibitory effect on pharyngeal cortical activity and swallowing. Moreover, Argyropoulos et al (2011) demonstrated that TBS of the right neocerebellar vermis can selectively disrupt the practice-induced acceleration of lexical decisions.…”

Metaplasticity in the human swallowing system: clinical implications for dysphagia rehabilitation

“…Interestingly, the effects of cerebellar neurostimulation appear to be site-specific. Studies have found that rTMS or tDCS applied over the midline of cerebellum result in suppressive effects on pharyngeal cortical excitability and swallowing behavior or skill learning [80,81]. While cerebellar neurostimulation may appear to have therapeutic potential for dysphagia, most of the data come from healthy volunteer studies.…”

A feasibility pilot study of the effects of neurostimulation on dysphagia recovery in Parkinson’s Disease

“…Pharyngeal recordings were made using a trans-nasally inserted intraluminal catheter (Gaeltec, Isle of Skye, UK) as described before 31 . APB EMG signals for recording APB MEPs were used as a control and acquired as previously reported 32 .…”

“…Following this, single-pulse TMS was used to locate pharyngeal motor cortical hotspots bilaterally and the APB motor cortical hotspot on the hemisphere with the lowest pharyngeal RMT. RMTs over pharyngeal and APB areas were determined as has been described in previous studies 32 .…”