Thesis (Ph. D.)--Harvard--Massachusetts Institute of Technology Division of Health Sciences and Technology, 2001.Includes bibliographical references (p. 147-154).The human tongue is a versatile, lithe and structurally complex muscular organ that is of paramount importance for many physiological tasks. The lingual musculature is composed of various orthogonally oriented myofiber populations. Furthermore, coupling this knowledge of tissue myoarchitecture with patterns of regional deformation offers the ability to explore complex structure-function relationships in the organ. Tongue myoarchitecture was studied with Diffusion Tensor MRI (DTI), which derived the spatial diffusion tensor field in the tongue. Since, diffusivity relates directly to myofiber orientation, this in vivo technique successfully produced a virtual anatomical atlas. In order to relate this 3D myoarchitecture to physiological deformations, in vivo strain was quantified by an MRI tagging technique. This technique tagged lingual tissue with a rectilinear grid, which was subsequently imaged to track and quantify deformation through 3D strain measures. Anterior protrusion, sagittal bending, and oral stage deglutition were studied with this technique. The results demonstrated that synergistic co-contraction between various muscle populations produced the necessary deformations in global tongue shape. In order to delineate specific muscular contributions to sagittal bending, the tongue was modeled by a thermal bimetal strip analog wherein thermal contraction approximated muscle fiber activation.(cont.) The results confirmed our hypothesis that sagittal bending resulted from synergistic co-contraction of two distinct myofiber populations. In conclusion, tongue deformation is intimately related to the lingual musculature, and our results confirm the characterization of the tongue as a muscular hydrostat - an organ whose musculature produces deformation as well as the structural support for that deformation.by Vitaly J. Napadow.Ph.D.