Functionally navigated transcranial magnetic stimulation to evoke lingual pressure in stroke survivors with dysphagia and healthy adults: a proof of concept trial

ABSTRACT

Background: Post-stroke dysphagia is characterized by reduced corticolingual excitability and lingual pressure; however, it remains unknown if transcranial magnetic stimulation (TMS) directly facilitates lingual pressure generation.

Objectives: To explore optimal procedures for single pulse TMS using neuronavigation to evoke lingual pressure in intact and disrupted neural networks.

Methods: Using co-registered functional magnetic resonance imaging, stimulation sites were determined for five healthy adults (Mage = 67) and four stroke survivors with dysphagia and reduced tongue strength (Mage = 66). Evoked lingual pressures were sampled across 45-65% of maximum stimulator output. Healthy participants repeated TMS with a bite block to isolate lingual pressure from off-target stimulation of mandibular elevators.

Results: Only one functionally-guided stimulation site fell within previously reported optimal lateral (8-11cm) and anterior (2–4.25cm) coordinates. Lingual pressure was stable prior to pulse and increased linearly with intensity for both groups (p = .005). Post-stroke active motor thresholds were elevated compared to healthy adults (p = .025). Lingual pressure latency remained stable across intensities (p > .05). Jaw stabilization via bite block reduced the mean magnitude of evoked lingual pressure by approximately 16%.

Conclusions: Single pulse TMS directly evokes higher lingual pressure and can define motor thresholds in intact and disordered corticolingual pathways. Stimulation sites using neuronavigation in healthy adults and stroke survivors largely differed from external coordinates in the literature that were predominantly established in young adults. Procedures to investigate motor thresholds for lingual pressure generation are proposed. The therapeutic role of TMS to address post-stroke deficits in lingual pressure and corticolingual excitability warrants continued investigation.

KEYWORDS:

• Dysphagia
• neuroimaging
• noninvasive brain stimulation
• transcranial magnetic stimulation
• neuronavigation
• lingual pressure
• tongue

Acknowledgments

We thank Dr. Todd Parish for his guidance and Madison Routier for her assistance in waveform analysis as well as express deep gratitude to the participants for their selflessness and generosity with their time and energies.

Disclosure of interests

The authors report no conflict of interest.

Additional information

Funding

This work was supported by the American Heart Association under Grant #13CRP17060043.