The coordination of rhythmical drinking behavior with swallowing in rabbits

To analyze the relationship between swallowing and rhythmical licking movement, jaw movement trajectories and muscle activities were recorded during water drinking in freely behaving rabbits. Three types of swallows were identified based on the configurations in thyrohyoid burst with the cycle phases. They were distinguished by whether the burst stayed in the opening phase; whether it continued over the opening phase until the closing phase; and whether it began in the closing phase and ended in the opening phase. The occurrence frequencies were 66%, 20%, and 14%, respectively, for the three types. The duration of the opening phase and burst durations in the jaw opening muscles in swallowing cycles were longer than those in licking cycles regardless when the swallow occurred. However, there were small influences of the thyrohyoid burst on a duration of the closing phase. The results suggest that during licking and swallowing, the digastric muscle may mainly work as a jaw opening-related muscle, and the mylohyoid muscle may work as both a jaw opening-related muscle and a swallowing-related muscle.