The tongue is critical for normal oromotor function in humans, yet we have only a limited understanding of human tongue neuromuscular organization and the bases for decline of tongue function with aging. Development of interventions for tongue dysfunction ;e.g., strengthening of tongue muscles to prevent dysphagia) are hindered because the anatomical and physiological targets of these interventions are not known. The long term goals of this study are to determine the neuromuscular organization of key functional elements of the human tongue muscle system and how these elements change with development and aging and to thereby improve clinical treatments for recovery of tongue dysfunction. To achieve these goals, this study applies anatomical, genetic, immunohistochemical, molecular and physiological techniques to the study of the adult and aged tongue in humans, macaques and rats. The results of these studies will meet three general aims. First, the architecture of tongue muscles will be studied to determine the structural bases of tongue movement diversity. Second, tongue muscle contractile and metabolic proteins will be studied to determine the molecular bases of age-related tongue dysfunction. Third, tongue motor unit activity patterns will be studied to identify physiological bases of age-related tongue dysfunction. These studies will provide important information on the neurobiology of the tongue motor system and will provide the first direct tests of the molecular and physiological bases of aging of the human tongue motor system.