The dynamics of lingual-mandibular coordination during liquid swallowing.
Previous literature on tongue-jaw relationships during swallowing has focused on behaviors observed with chewable solid foods. The present investigation was undertaken to evaluate both the nature and stability of coordinative relationships between the jaw and three points located along the midsagittal groove of the tongue--anterior (blade), middle (body), and posterior (dorsum)--during swallowing of thin and honey-thick liquids. A reiterative swallowing paradigm was used, with two task conditions (discrete and sequential), to explore the stability of tongue-jaw coordination across different frequencies of swallowing. Eight healthy participants in two age groups (young, older) performed sets of repeated swallows. Tongue and jaw movements were measured using electromagnetic midsagittal articulography. The data were analyzed in terms of variability in the spatiotemporal movement pattern for each fleshpoint of interest, and the temporal coupling (frequency entrainment) and relative phasing of movement for each tongue segment compared to the mandible. The results illustrate a stereotypical but not invariant sequence of movement phasing in the tongue-jaw complex during liquid swallowing and task-related reductions in variability at higher frequencies of swallowing in tongue dorsum movements. This evidence supports the idea that different segments of the tongue couple with the jaw as a synergy for swallowing, but can modify their coupling relationship to accommodate task demands.