Vibration over the larynx increases swallowing and cortical activation for swallowing

Abstract

Sensory input can alter swallowing control in both the cortex and brainstem. Electrical stimulation of superior laryngeal nerve afferents increases reflexive swallowing in animals, with different frequencies optimally effective across species. Here we determined 1) if neck vibration overlying the larynx affected the fundamental frequency of the voice demonstrating penetration of vibration into the laryngeal tissues, and 2) if vibration, in comparison with sham, increased spontaneous swallowing and enhanced cortical hemodynamic responses to swallows in the swallowing network. A device with two motors, one over each thyroid lamina, delivered intermittent 10-s epochs of vibration. We recorded swallows and event-related changes in blood oxygenation level to swallows over the motor and sensory swallowing cortexes bilaterally using functional near infrared spectroscopy. Ten healthy participants completed eight 20-min conditions in counterbalanced order with either epochs of continuous vibration at 30, 70, 110, 150, and 70 + 110 Hz combined, 4-Hz pulsed vibration at 70 + 110 Hz, or two sham conditions without stimulation. Stimulation epochs were separated by interstimulus intervals varying between 30 and 45 s in duration. Vibration significantly reduced the fundamental frequency of the voice compared with no stimulation demonstrating that vibration penetrated laryngeal tissues. Vibration at 70 and at 150 Hz increased spontaneous swallowing compared with sham. Hemodynamic responses to swallows in the motor cortex were enhanced during conditions containing stimulation compared with sham. As vibratory stimulation on the neck increased spontaneous swallowing and enhanced cortical activation for swallows in healthy participants, it may be useful for enhancing swallowing in patients with dysphagia. NEW & NOTEWORTHY Vibratory stimulation at 70 and 150 Hz on the neck overlying the larynx increased the frequency of spontaneous swallowing. Simultaneously vibration also enhanced hemodynamic responses in the motor cortex to swallows when recorded with functional near-infrared spectroscopy (fNIRS). As vibrotactile stimulation on the neck enhanced cortical activation for swallowing in healthy participants, it may be useful for enhancing swallowing in patients with dysphagia.