Cerebellar Metaplasticity in the Swallowing Motor System

Dysphagia is common and leads to significant morbidity and mortality within healthcare settings. Current approaches to dysphagia management involve altering the consistency of food and fluids. However, these approaches are not supported by a robust evidence base. Repetitive transcranial magnetic stimulation (rTMS) offers a non-invasive way to manipulate neuroelectric activity within the brain. Within the swallowing motor system, rTMS at a frequency of 5Hertz (Hz) and above is excitatory while 1Hz is suppressive.

Cortical rTMS targeting pharyngeal motor areas can alter brain activity and swallowing behaviour in healthy participants and has been shown to improve post-stroke dysphagia (PSD). Despite this, it has a small seizure risk. Cerebellar rTMS is a newer and safer technique which is more easily targeted and is effective at altering swallowing related brain activity and behaviour. Recent studies have also shown it can improve PSD.

Critically, individual responsiveness to rTMS is variable, potentially reducing its effectiveness. Metaplasticity whereby the brain is preconditioned with a neuroelectric stimulus before the treating stimulus is administered is a potential way of reducing variability. Metaplasticity has recently been shown to improve responses within the swallowing motor system following cortical rTMS. However, to date no cerebellar rTMS study has applied this approach. This is a gap in our understanding which will need to be addressed.

The overarching aim of the study is to develop a less variable and more effective treatment for neurogenic dysphagia. More specifically the study objectives are to establish:

1. Whether 10Hz Cer-rTMS delivered over hemispheric pharyngeal areas can induce SMS metaplastic changes in healthy participants. 2. If a cerebellar rTMS metaplastic stimulation protocol can affect swallowing behaviour.