Basic NeuroscienceThe effect of swallowing treatments on corticobulbar excitability: A review of transcranial magnetic stimulation induced motor evoked potentials

- MEPs are used with increasing frequency in swallowing research.
- The link between cortical excitability and functional swallowing behaviour is unclear.
- Large standard deviations are typical of MEPs recorded from swallowing muscles.
- Analysis characteristics need to be clearly defined for comparison between studies.
- A review of considerations specific to swallowing related MEPs is provided.

Transcranial magnetic stimulation (TMS) has been used extensively as a method of investigating the corticomotor physiology of many motor tasks, including healthy and disordered swallowing. Changes in excitability of cortical projections to various swallowing muscles have been documented in response to treatments with TMS induced motor evoked potentials (MEPs). These studies have provided valuable insight into CNS response to swallowing impairment, and more importantly, the adaptations associated with functional recovery. However, unique obstacles are presented when investigating corticobulbar neurophysiology associated with the complex task of swallowing. Stringent methodological control and supplementary outcome measures are required to ensure robust and clinically applicable findings. This article offers a tutorial for the researcher who may be considering the use of TMS for investigating changes in cortical excitability associated with various swallowing paradigms. Included is a review of the mechanisms of TMS and what can be measured with this technique, a summary of existing research using MEPs to investigate swallowing, a review of methodological factors that may influence outcomes, and proposed directions for new areas of research.