Temporomandibular disorders (TMD) represent a group of chronic painful conditions in the masticatory musculature and temporomandibular joint. To examine possible changes in cortical machinery in TMD patients, we compared neuromagnetic signals evoked by cortical neurons between healthy subjects and TMD patients while they were carefully observing the video frames of jaw-opening movements performed by another person. During the movement observation task in the healthy subjects, we found cortical activation in the following sequence with left hemisphere dominance: (1) the occipitotemporal region near the inferior temporal sulcus (human homologue of MT/V5 in monkeys), (2) the inferior parietal cortex (IPC), and (3) the anterior part of the inferior-lateral precentral gyrus (PrCG). In the TMD patients, however, we found deficit or marked attenuation of the neuromagnetic responses in the PrCG and IPC, while the activity of the MT/V5 showed no differences from that in the healthy subjects. In addition, we could not find any differences in cortical magnetic responses between healthy subjects and TMD patients when they were observing palm-opening movements, indicating that cortical dysfunction associated with jaw-movement observation is specific phenomena in the patients of TMD. Thus the present study provides new neuropathological evidence that TMD patients exhibit dysfunction of recognition mechanisms in cerebral cortex during motor observation, and suggests that disturbance of cortical functions regulating visuomotor integration would play a crucial role in development as well as aggravation of TMD.
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