Chewing Well Modulates Pharyngeal Bolus Transit During Swallowing in Healthy Participants

Mastication is controlled by central pattern generator in the brainstem and can be modulated by volition. The aim of this study was to investigate the effect of chewing well on swallowing. Twenty-six healthy participants were instructed to eat 8, 12, and/or 16 g of steamed rice with barium sulphate under the following two conditions: chewing freely task (CF; chewing naturally in their usual manner) and chewing well task (CW; chewing the food with a request to "chew well"). We evaluated bolus transport and swallowing movement using videofluoroscopy and electromyography of the masseter, suprahyoid and thyrohyoid muscles. The chewing time and pharyngeal transit time (PTT) at the first swallow showed high reproducibility in both CF and CW. PTT for CW was significantly shorter and longer than CF in 12 and 16 g, respectively. In 12 g, CW increased the pharyngeal bolus velocity and decreased thyrohyoid EMG activity during swallowing compared with CF. In 16 g, the difference between CW and CF in the estimated swallowed bolus volume was positively correlated with that in upper esophageal sphincter transit duration. We speculate that CW modulates PTT during swallowing depending on the mouthful volume.