Using tagged cine-MRI and finite-element method to lower bound the number of independently controllable motor units in the tongue

• Published in: The Journal of the Acoustical Society of America Vol. 120; no. 5_Supplement; p. 3371
• Main Authors: Essex-Torcaso, Caroline, Levine, William S., Stone, Maureen, Murano, Emi Z., Parthasarathy, Vijay, Prince, Jerry L.
• Format: Journal Article
• Language: English
• Published: 01-11-2006
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4781560

The biomechanical structure of the tongue is unusual in that there is no rigid structure, such as a bone, for the muscles to act against. In order to understand these biomechanics and their control, a mathematical model has been created. This model has the form of a nonlinear controllable incompressible elastic structure that undergoes large deformations. The model was used to solve a simplified two-dimensional inverse problem. For a simple speech motion (/i-u/), the trajectories of specific points within the tongue were tracked by means of tagged cine MRI. These points correspond to finite element nodes and were used as input to the simplified model. The remaining unknowns in the model are the set of muscle activations that produce the observed motion. Because there is no such set of activations, the set that best approximates the observed motion in a least squares sense was chosen. The results indicate that there must be independently controllable compartments in SL and GG in order to produce this movement. Three methods were used to improve the representation of the tongue and the resolution of the model: refinement of the number of elements, refinement of the number of muscle activations, and the inclusion of dynamics.