The goal of the proposal is to understand how muscle pain associated with temporomandibular disorders (TMD) affects neuromotor performance in primates. Current evidence suggests that at least some myogenous jaw pain in humans causes a protective adaptation response, in which there is decreased activity in agonist muscles, and increased activity in antagonist muscles, resulting in restricted ranges of jaw motion. Currently, a hypothetical brainstem model has been proposed to explain this, but it is equally possible that higher levels of motor control are involved, such as the motor cortex, in addition to, or instead of, the brainstem. Though conscious responses to pain, and control of jaw muscle contraction both involve the sensorimotor cortex, the region's potential contribution to the protective adaptation response has not been studied. Since the applicants have developed a suitable animal model for producing transient jaw muscle pain in the awake monkey (Macaca mulatta) and for observing its effects on voluntary jaw motion and jaw position, the first aim therefore is to carry out a parametric analysis of normal jaw motion and muscle activity during stereotyped motor tasks and automatic chewing, and to repeat the experiment in the presence of induced muscle pain.
The second aim i s to define relationships between the types and locations of corticomotoneuronal activity, and the same peripheral variables associated with these acts in normal animals.
The third aim i s to repeat this study of the motor cortex in the presence of induced muscle pain. The applicant hypothesizes that cortical neurons provide signals correlated with the initiation and execution of jaw movements and the maintenance of jaw positions, and that the signals change during the conscious pain experience in such a way as alter muscle contraction patterns, and subsequent jaw motion. They consider that their preliminary data support this proposition. The alternative hypothesis proposed is that this change in cortical signalling does not occur, in which case the applicant will conclude that the pain-adaptation response is due primarily to brainstem mechanisms. The applicant believes the study is significant because it can provide a better understanding of cortical influences in the control of jaw movement generally, and in particular, define the cortex's role in human motor responses to jaw muscle pain.
