The Neural Substrates of Adaptive Jaw Movement

Miami University Oxford, Oxford OH

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Abstract

DESCRIPTION: Dental health research requires not only clinical studies on preventive and restorative care, but also systematic growth in our basic understanding of the anatomy, physiology, and behavior of orofacial systems. Continued basic research is essential, ranging from systems analysis of normal structure and function to investigation of the processes of adaptation following disease, aging, or dental treatments. A critical aspect of this inquiry is the investigator's understanding of the neural control of rhythmic or complex mouth movements such as chewing or speaking. While animal models of speaking movements have obvious limitations (and, in humans, speaking and masticatory movements are controlled differently), a number of models exist for studying the sensory, motor, neural and adaptive bases of mastication in animal preparations. Mastication is one neurobehavioral system that is affected by aging and disorders such as temporo-mandibular joint malfunction, stroke, Huntington's and Parkinson's diseases, and difficulty adapting to dental implants. Advancements in our basic knowledge of jaw movement control systems will suggest and improve treatments for these and other disorders. The specific aims of this project are: 1) to continue the examination of the relationships between limbic and motor neural responses and the conditioning of adaptive jaw movements in awake, undrugged rabbits. The proposed project will incorporate single unit recording via a chronically implanted microdrive system that will allow sequential isolation of several single units as an animal performs at criterion levels on the task. In doing so, we will be developing this model system as a complement to studies ofjaw movements in anesthetized preparations; and 2) to replicate and extend our findings on the impact of aging and cholinergic dysfunction on jaw movements by comparison of the reflexive and conditioned responses exhibited by rabbits with drug-induced impairment of important cortical masticatory areas (CMAs). This analysis will include precise, three- dimensional analysis of reflex responses to food and water as well as the dynamics of each subject's adaptation to the timing required for successful conditioned responding. These aims will be addressed in the context of recording neural and behavioral activity simultaneously during jaw movement training in rabbits. Classical conditioning of rhythmic jaw movements has been developed as a model system for evaluation of the neural bases of reward learning. It is a very well-controlled form of adaptive behavior that facilitates discrimination among sensory, motor, motivational and cognitive processes involved in ongoing behavior. Characterization of the brainstem neurobehavioral control systems and their modulation by the forebrain will provide a necessary foundation for the application of this model system to health-related research.