Modulation of voluntary swallowing by visual inputs in humans

The purpose of this study was to test the hypothesis that a stimulus which strengthens a central input to a swallowing-related cortical area, given before voluntary swallowing, could facilitate subsequent swallowing movements. The subjects consisted of seven healthy volunteers. We used visual images to strengthen central input. The subjects voluntarily performed either dry swallowing or water swallowing after presentation of the visual images. Under the water-swallowing condition, the latency was significantly shorter and the maximum amplitude of the suprahyoid electromyographic (EMG) activity was significantly smaller in subjects who received drink-related visual input. However, there were no similar differences under the dry-swallowing condition. In addition, there were no significant differences in the mean EMG amplitude or the duration of EMG activity between subjects who did and did not receive drink-related visual input under either swallowing condition. We concluded that drink-related visual inputs prior to voluntary swallowing facilitate the initiation of swallowing and enhance swallowing-related muscle activity in the presence of peripheral inputs.