Effects of olfactory and gustatory stimuli on neural excitability for swallowing.

This project evaluated the effects of olfactory and gustatory stimuli on the amplitude and latency of motor-evoked potentials (MEPs) from the submental muscles when evoked by transcranial magnetic stimulation (TMS). Sixteen healthy volunteers (8 males; age range 19-43) participated in the study. Lemon concentrate at 100% and diluted in water to 25% were presented separately as odor and tastant stimuli. Tap water was used as control. 15 trials of TMS-evoked MEPs triggered by volitional contraction of the submental muscles and volitional swallowing were measured at baseline, during control condition, during stimulus presentation, and immediately, 30-, 60-, and 90-min poststimulation for each of the four stimulus presentations. Experiments were repeated using the combined odor and tastant concentrations that most influenced the MEP independently. Differences in MEP amplitude measured during swallowing were seen at 30-, 60-, and 90-min poststimulation for simultaneous olfactory and gustatory stimulation as opposed to no differences seen at any point for stimuli presented separately. This study has shown that combined odor and tastant stimulation (i.e., flavor) can increase MEP amplitude during swallowing and that this enhancement of MEP can persist for at least 90min following stimulation. As increased MEP amplitude has been associated with improved swallowing performance, a follow-up study is underway to determine the biomechanical changes produced by altered MEPs to facilitate translation of these data to clinical dysphagia management.