Quantitative model of jaw proprioception during active movements

点击翻译按钮获取中文摘要

PROJECT SUMMARY Proprioception is an indispensable sense of the body’s position and movement in space. Fine motor control depends on proprioceptors to monitor the mechanical consequences of motor actions. In particular, muscle spindles are a class of primary proprioceptors that detect muscle length and stretch at the intrafusal fibers. The signals generated by muscle spindles are complex with dynamical regulation of intrafusal fiber lengths via γ motor neuron (fusimotor) activity. The interaction between feedforward mechanical signals at the muscle spindle and descending motor commands at the parent muscle, especially in the context of naturalistic movements, remains poorly understood. Opposing views disagree on whether muscle spindles passively sense muscle length/stretch or actively process biomechanical signals based on motor commands to the muscle. Using the unique advantages of rodent jaw proprioceptors in the hindbrain mesencephalic trigeminal (MeV) nucleus, I will test the hypothesis that motor commands flexibly tune jaw muscle spindle coding in a context-dependent manner. With experimental access to many levels of the jaw sensorimotor circuit, I will determine how feedforward mechanical signals and descending motor commands interact at the primary proprioceptors. Aim 1 will find the relationship between motor unit activity in jaw muscles and corresponding muscle spindle activity during passive and active movements. Aim 2 will record muscle spindle activity with (a) external loads on the jaw and (b) optogenetic decoupling of motor drives from muscle-driven motion. Aim 3 will provide an overarching framework to model the jaw system as a feedback control loop. The proposed project investigates proprioceptive feedback in craniofacial structures, electrophysiological mechanisms for controlling jaw function, and quantitative models of the neural controller and muscles of the jaw. The immense training potential in this project lies in the application of novel in vivo electrophysiology tools, well-designed use of optogenetics, and quantitative modeling rooted in control theory. The proposed work has important implications in elucidating orofacial proprioception at the primary receptors and understanding temporomandibular disorders and orofacial pain involving maladaptive control of the jaw.