Figure 2: Schematic illustration of the experimental protocol. At the beginning of each session, the threshold (T) of the swallowing reflex is determined. Then electrical stimulation alone (ES alone) was applied to oropharynx for 15 s. This procedure was repeated three times with 18 s interval, and the mean latency was calculated and defined as pre-control. Then one of the test solutions was applied to the oropharynx in addition to 15 s electrical stimulation (ES+A). The test solution was injected approximately 1 s prior to electrical stimulation. This procedure was also repeated three times with 18 s interval, and other solutions were also tested in the same manner (ES+B, ES+C and ES+D). After testing all test solutions, the electrical stimulation alone was again applied three times to the oropharynx (ES alone), and the mean latency for the reflex was calculated as post control.