| The tongue functions as the primary articulator during deglutition, responsible both for controlled bolus transfer from the mouth to the pharynx, and for initiation of the pharyngeal phase of swallowing. Several authors have proposed that swallowing behaviours are modifiable, and vary across tasks. These assumptions form the basis for many clinical intervention strategies in dysphagia management. This research sought empirical evidence of systematic modulation in oral motor behaviours in swallowing, related to manipulations of task (rate) and bolus characteristics.; Electromagnetic midsagittal articulography (EMMA) was used to trace tongue and jaw movements during swallowing. Eight healthy subjects, in two age-defined cohorts (under 30; over 50) participated. A data corpus of approximately 4400 swallows was collected.; Analysis of a discrete water swallow reference task (chapter 2) demonstrates the validity of the EMMA method for characterizing tongue behaviours during swallowing, and shows stability in swallowing behaviours across sessions. A comparison of discrete and sequential swallows (chapter 3) failed to find evidence of frequency-dependent scaling in movement amplitudes. Rather, subjects showed economy of effort (fewer movement oscillations per swallow) and simplification of the motor pattern (reduced variability in tongue and jaw movements) as the rate of repeated swallowing increased. Similarly, higher frequencies of swallowing were associated with reduced variability in coordinative relationships between different segments of the tongue and the jaw (chapter 6).; With respect to the influence of bolus consistency on swallowing behaviours, a previously unreported phenomenon of bolus density-related modulation in sip-size is described. Limited evidence of bolus consistency influences on the spatio-temporal characteristics of tongue behaviours during swallowing was observed (chapters 4, 5).; Age-cohort differences were evident throughout this investigation. Older subjects produced a higher number of movement oscillations per swallow and showed greater variability in oral motor behaviour for swallowing. Scaling of tongue movement amplitudes to bolus size was observed only in younger subjects.; In the concluding chapter, the potential for using EMMA to elucidate future research questions regarding oral motor modulation in swallowing is explored. A coordinative dynamics model is proposed to account for reported variations in the timing of pharyngeal swallow initiation across boluses of different consistency. |
