Jaw-tongue coordination during chewing in Pigs

Abstract

Jaw movements during mammalian chewing drive occlusion and food breakdown. As important as jaw movements are for chewing, soft tissues within the oral cavity are essential for handling the food bolus throughout the chewing sequence. For instance, tongue movements and deformations (1) position the food between the tooth rows, (2) help mix the bolus with saliva to initiate digestion and improve swallowability, and (3) transport the bolus to the oropharynx to initiate the swallow. Tongue movements and deformations must be coordinated with jaw movements to ensure chewing performance and efficiency as well as to avoid self-injury, and previous research shows that disruption of the sensory input from the tongue alters jaw movements during chewing in pigs. Even though jaw and tongue movements during mammalian chewing are investigated extensively, their coordination pattern(s) have received less attention. We present three different approaches to quantify the correlation between jaw movements (opening and closing, mediolateral deviation) and tongue movements (positional changes such as protraction-retraction) and deformation (length and width changes) during chewing in pigs. At the sequence level, cross-correlations are used to calculate the lag in time between tongue and jaw kinematics. Cross-correlation analyses can also be carried out at the cycle level, albeit with less statistical power. Finally, functional data analysis standardizes and resamples the data to test for jaw-tongue correlation at each time point, essentially testing bivariate correlation continuously throughout the chewing cycle. We discuss the benefits and limitations of each methodology to emphasize the impact of combining analytical tools.