Meeting Abstract
The link between hyoid posture and muscle behavior may be dynamic across the many vital behaviors that involve the hyoid. Previous research has shown that, in primates, hyoid translations during swallows are larger than those of other feeding behaviors (e.g., chewing), but whether and how such translations relate to muscle function is unknown. We integrated XROMM, contrast-enhanced CT, and EMG to examine the relationship between in vivo muscle length changes, line of action, and activity patterns in two hyoid muscles (mylohyoid and geniohyoid) during 50+ chewing and swallowing cycles in Macaca mulatta. Different hyoid postures had different muscle orientations, particularly in mylohyoid during swallows. Anteroposterior displacement and velocity of the hyoid can be accounted for by changes in geniohyoid length and velocity alone in both chews and swallows. However, superoinferior displacement and velocity of the hyoid cannot be accounted for by mylohyoid length and velocity alone in swallows. Additionally, there is a stronger correlation between mylohyoid fiber angle (i.e., fiber rotation) and hyoid superoinferior position during swallows than chews. Timing of high hyoid elevation velocity with lower mylohyoid shortening velocity corresponds with high mylohyoid activation, further suggesting that fiber rotation is functionally important in swallows. The results suggest that geniohyoid function is robust to changes in hyoid posture while mylohyoid function is more dynamic. Muscles with simple fiber architecture may be able to generate different behaviors through a more complex interaction of shortening and fiber rotation.
