The present study tested whether electrical stimulation increases the number of voluntary repetitive swallows in humans. In addition, the potential of initiating both voluntary and involuntary swallows was compared using electrical stimulation. Fourteen normal male adults were instructed to perform repetitive voluntary swallowing as quickly as possible over 30 s, and the number of swallows was counted with and without repetitive electrical stimulation (80% of maximal tolerated intensity; 0.1 ms in pulse duration; 30 Hz) of the nasal cavity, nasopharynx, oropharynx, or laryngopharynx. Although the number of swallows was significantly increased during electrical stimulation of the laryngopharynx, oropharynx, and nasopharynx, there was a wide variation in the number among subjects. The number of reflexively evoked swallows (i.e., involuntary swallows) by pharyngeal stimulation also varied greatly, and there was a significant linear correlation in the number of swallows between voluntary and involuntary swallows. The present study demonstrated the facilitatory effects of pharyngeal electrical stimulation on voluntary swallowing in humans. Furthermore, the potentials of initiation of voluntary swallows are identical to those of involuntary swallows, which suggests that the swallowing central pattern generator is a common component of both neuronal networks and therefore is responsible for inter-individual variations.
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