Impaired chewing, swallowing as a result of orofacial or CNS injury or disease is a worldwide health problem that can impact quality of life and even be life-threatening. Current rehabilitation of such impairments has largely overlooked recent advances in neurorehabilitation of limb motor control which may explain why many patients cannot regain normal chewing and swallowing. The oral primary motor cortex (oM1) is the main brain region involved in the generation and control of orofacial movements. However, detailed baseline 3D kinematics and EMGs of aerodigestive and craniofacial structure as a whole which is to be compared to the pathological cases is lacking. Detailed characterization of modulations of local field potentials (LFPs) to gape types remains unclear. Furthermore, detailed kinematic and EMG encoding in single unit spiking activities for any orofacial behavior has not been performed. Lastly, relation between LFPs and muscle activities has not been explored except for beta oscillation and tongue muscles. Thus, to fill in the gap in our knowledge, our specific aims are:
AIM 1 : To characterize and quantify 3D kinematics of aerodigestive and craniofacial structures and jaw and tongue electromyographic (EMG) activities during natural feeding in awake rats. We will utilize our documented expertise with 3D high-speed videofluoroscopy and chronically implanted jaw/tongue EMG electrodes. We will: (a) characterize gape cycle types (e.g., chewing, swallowing) during feeding and how epiglottal and vocal fold open/closure are timed at each of the cycle types; and (b) perform dimension reduction techniques on both kinematics and EMGs to obtain a set of principal movements and EMG activities for each cycle type and transitions between cycle type.
AIM 2 : To relate the jaw/tongue EMG and 3D kinematics of aerodigestive and craniofacial structures to simultaneously record neural activities within multiple oM1 sites and layers in awake rats, and test if and how oM1 neural activity properties are related to tongue and jaw EMG and 3D kinematics of aerodigestive and craniofacial structures during feeding. We will utilize our documented expertise with chronically implanted microelectrode arrays that span horizontally and vertically into oM1 layers 2/3 (mainly cortico-cortico projections) and 5/6 (mainly output projections). We will then: (a) characterize how LFP profiles are related to types of gape cycles and their transitions between them; (b) characterize how kinematic- and EMG activities are encoded in single unit spiking activity of oM1; and (c) characterize cortico-muscular coherence between oM1 LFPs and jaw/tongue EMG activities for each gape type. This proposal will define a new 3D kinematic characterization of aerodigestive and craniofacial structures during feeding and novel oM1 neural mechanisms in terms of modulations of LFPs to gape cycles and single unit spiking activity encoding of kinematics and EMG based on layers. Better understanding of such mechanisms is needed to develop improved prevention and management of impaired motor functions resulting from oral injury, possibly by targeting oM1 neural processes.
The oral primary motor cortex is a brain region that plays a crucial role in the generation and control of orofacial movements. Our studies in awake rats employ 3D x-ray video recording to test if jaw and tongue movements during natural feeding are altered following tooth loss, and if, when and how these changes are related to changes in the activity of neurons within the oral primary motor cortex. This information is important since impaired chewing and swallowing as a result of tooth loss, neurological disorders or aging are common clinical occurrences, and our studies will provide new knowledge of how subjects adapt or not to tooth loss, and thereby contribute to the development of improved clinical approaches aimed at rehabilitation of oral sensorimotor functions.