We investigated (1) how peripheral inputs might assist central inputs in the control of voluntary evoked swallowing, (2) inter-individual variation in involuntary and voluntary swallowing initiation, and (3) whether natural chewing behavior affects the initiation of involuntary swallowing in healthy humans. Eleven participants completed a repetitive saliva swallowing test (RSST), chewing test (CHEW), and rest period (REST). In RSST, participants repetitively swallowed as quickly as possible. In CHEW, subjects chewed gum freely. We delivered pharyngeal electrical stimulation (PEStim) to the laryngopharynx and compared the number of swallows that occurred with and without PEStim. PEStim significantly increased the number of voluntary evoked swallows in RSST, as well as the number of swallows in CHEW and REST trials, although this facilitatory effect was larger in REST trials. We found a positive correlation between the number of swallows at RSST without PEStim and that at REST with PEStim within individuals. Additionally, we found a significant positive correlation between the number of swallows at RSST with PEStim and the sum of that at RSST without PEStim and at REST with PES. Based on the current results, we suggest that (1) peripheral inputs within a certain range appear to facilitate the central inputs that control voluntary swallowing, (2) inter-individual variations in swallowing initiation may arise from differences in the excitability of the common neural network in the lower brainstem, and (3) during chewing, food reduction in the oral cavity is prioritized, such that the neural network associated with chewing may regulate swallowing initiation.
Keywords: Chewing; Involuntary swallow; Pharyngeal electrical stimulation; Voluntary swallow.
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