Dental health research requires not only clinical studies, but also systematic growth in our basic understanding of orofacial systems, including analysis of normal structure and function as well as investigation of the processes of adaptation following disease, aging, or dental treatments. A critical aspect of this inquiry is our understanding of the neural control of complex mouth movements, such as chewing. A number of models exist for studying mastication in animal preparations. Mastication is affected by aging and disorders such as temporo-mandibular joint malfunction, stroke, neurodegenerative diseases, and difficulty adapting to dental implants. Advancements in our basic knowledge of jaw movement control systems will improve treatments for these and other disorders.
The specific aims of this project are: (a). to investigate the roles of two neural structures--the anterior cingulate cortex (ACC) and amygdala (AMYG) - in the conditioning and extinction of adaptive jaw movements in unanesthetized, behaving rabbits. These limbicforebrain areas may be especially important in our understanding of higher order orofacial neural control systems in that they are involved in the emotional and associational processing of pain input from the jaw, are essential to the extinction of maladaptive jaw movement responses, and are surprisingly direct in their connections to the trigeminal neurons that control jaw movements. The proposed project will utilize a state of the art multiple single unit recording system that allows simultaneous isolation and physiological monitoring of several single neurons. (b). to extend our findings on the contributions of forebrain systems to adaptive and dysfunctional jaw movements (JMs) by comparing the reflexive and conditioned responses exhibited by rabbits following infusion of drugs in microliter doses directly into ACC or AMYG. Such microinfusions, via chronically implanted cannulae, are a powerful improvement over systemic injections--one that definitively localizes the pharmacological treatment to a single neural structure, thereby minimizing side effects and permitting strong conclusions about the neural substrates of behavioral effects. Our strategy is to selectively modify the neurochemistry of these two forebrain areas via microinfusions that may, in pathologies such as temporomandubular joint disorder and other orofacial diseases, participate in a vicious cycle of maladaptive motor patterns induced by pain or sensorimotor imbalance. The effects of such micro infusions on behavioral adaptation and on cellular neurophysiology will be assessed. In addition to investigating reflex and conditioned responses during the initial training, we will determine the effects of these manipulations on behavioral and neural adaptation to subsequent changes in the timing demands of the task, and during extinction of the response induced by withdrawal of the rewarding oral stimulus that motivates the behavioral adaptation.
These aims will be addressed in the context of recording neural and behavioral activity simultaneously. 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.
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| Asaka, Y; Seager, M A; Griffin, A L et al. (2000) Medial septal microinfusion of scopolamine disrupts hippocampal activity and trace jaw movement conditioning. Behav Neurosci 114:1068-77 |
| Seager, M A; Asaka, Y; Berry, S D (1999) Scopolamine disruption of behavioral and hippocampal responses in appetitive trace classical conditioning. Behav Brain Res 100:143-51 |
