The long-term objective of the proposed experiments is to elucidate the role of sensory feedback in motor behavior.
The specific aim of these experiments is to determine if the directional and force feedback signal coded in the tooth mechanoreceptors is utilized in the short-latency reflex control of jaw movement. If directional feedback from these receptors is utilized, then tooth displacement will elicit reflex responses which appropriately reorient the jaw. If the force feedback signal is utilized, then a positive feedback loop is proposed via the lowest-threshold tooth mechanoreceptors coupled with an inhibitory response as higher-threshold receptors are activated to limit the magnitude of biting force. Two studies are proposed to test these hypotheses: 1) Extracellular recordings will be made from single jaw- elevator motor units during tooth displacement to determine the relationship among the magnitude and direction of tooth displacement,the level of inhibition or excitation of motor unit firing, and the anatomical location of the motor unit. 2) Intracellular recordings will be made from trigeminal motorneurons during the activation of tooth mechanoreceptors to determine the relationship among the magnitude and direction of tooth displacement, motorneuron membrane potential, and the type and anatomical location of the motor unit. The results from both of these studies will be used to determine if the reflex responses elicited by tooth mechanoreceptors are capable of providing directional feedback to guide jaw movement and/or force feedback to modulate the magnitude of bite force. These results will not only lead to a better understanding of the role of proprioceptive feedback in jaw movement, but may also be applied to determining the effects of tooth loss on sensory input and the role of tooth mechanoreceptor feedback in bruxism.
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