Tempospatial Linkage of soft palate and jaw movements in feeding

Abstract

【Purpose】The soft palate (SP) rises as the jaw opens and it falls as the jaw eloses during mastication. During swallowing, the SP elevates to seal the nasopharynx while jaw is closed. We examined the amplitude of SP movement and the temporospatial relationship between SP and jaw movement during feeding using cross-correlation analysis.

【Methods】Videofluorography in lateral projection was performed on 15 healthy volunteers (9 male and 6 female, mean 25 years old) eating 6 g of banana, chicken spread and cookie. A small radiopaque marker at the tip of a thin flexible rubber tube was passed transnasally to the superior surface of the SP. Additional markers were glued to upper and lower teeth. The SP and jaw marker positions were measured frame by frame and transformed into Cartesian coordinates. A feeding sequence was divided into three stages：food processing, oropharyngeal aggregation time, and swallowing. The highest and lowest points of SP movement were measured for each stage. The relationships between motions of the SP and jaw were quantified with cross-correlation functions.

【Results】There was cyclic motion of the SP in 50% of jaw cycles during processing and oropharyngeal aggregation cycles, with the lower jaw descending as the SP rose. The frequency of SP movement differed significantly among subjects (P＜0.001), but not among stages or foods. The amplitude of SP elevation gradually increased as the sequence progressed from processing to swallow (P＜0.001), The amplitude was higher with cookie than banana or chicken spread (P＜0.05). Cross-correlation coefficients were negative between motions of the jaw and SP during processing and aggregation (mean R ＝ －0.41 ± 0.24 and －0.42 ± 0.18, respectively). Jaw opening followed SP elevation by 0.10s during processing and 0.07s during aggregation. In contrast, SP-Jaw movement cross-correlations in swallowing were positive (mean R ＝ 0.49 ± 0.30) and SP elevation followed jaw closure by 0.13s.

【Conclusion】This study confirms and quantifies the temporospatial linkage between SP and jaw motion reported previously. The contrasting temporal linkages during mastication and swallowing suggests that different neural mechanism generate the motions of the SP during these two behaviors. The increase in SP displacement in later cycles may facilitate bolus transport by opening the fauces, and additionally provide a route for odors to reach the nasopharynx.