Temporomandibular Disorders (TMD) and other chronic pain disorders are associated with altered brain anatomy. A recent paper by Moayedi and colleagues expands knowledge in this area by describing the changes in white matter tract anatomy in TMD patients compared with healthy controls (healthy people without TMD). White matter tracts consist of the neuronal connections between different parts of the brain. MRI scans can indicate a loss or gain of these connections, local swelling or shrinkage of the nerve fibers, as well as the connections between different regions.
Moayedi et al. first examined changes in the trigeminal nerve, which contains the fibers responsible for transmitting pain and non-pain signals from the face to areas of the trigeminal brainstem complex, from which point signals are transmitted to the thalamus and other regions of the brain. They found that people with TMD had decreased white matter signals in the trigeminal nerve and that this decrease depended upon how long a patient had TMD—the longer one had suffered from TMD, the less white matter was in the nerve. It not is clear whether and how this finding is directly related to the TMD pain experience.
It's possible that the abnormality is important for the development and maintenance of pain, but that mechanisms higher up in the brain are responsible for the pain TMD patients experience. Moayedi et al. examined white matter changes in the brain and found decreased white matter across the whole brain, particularly near areas known to be involved in the experience of pain, including the brainstem, thalamus, insula, and somatosensory and cingulate cortices, as well as prefrontal cortical areas. White matter changes in some of these regions correlated with patients’ TMD pain or unpleasantness ratings, thus suggesting a link between altered anatomy and symptoms. Previous work from the same group of researchers showed altered gray matter in similar parts of the brain in people with TMD; the current study provides more details on the structural brain changes that occur with TMD.
Finally, Moayedi and colleagues reported altered connectivity to prefrontal regions, including a decrease in connectivity to the dorsolateral prefrontal cortex (DLPFC) and increased connectivity to the frontopolar cortex (FPC) in TMD patients compared to controls. The DLPFC and FPC are both implicated in various aspects of cognitive function (all aspects of perception, thinking, reasoning, and remembering), and these structural abnormalities could be related to the difficulty that some people with TMD have in performing a cognitive task, a finding the same laboratory previously reported.
While this study advances our understanding of structural brain abnormalities associated with TMD, future research will need to clarify the relationship of brain function and structure and TMD symptoms, as well as the effect of treatment on these brain alterations.
We thank David A. Seminowicz, Ph.D., Assistant Professor, Department of Neural & Pain Sciences, University of Maryland School of Dentistry, for writing this summary article.
Source: Moayedi M, Weissman-Fogel I, Salomons TV, Crawley AP, Goldberg MB, Freeman BV, Tenenbaum HC, Davis KD, White matter brain and trigeminal nerve abnormalities in temporomandibular disorder, Pain. 2012 Jul;153(7):1467-77.doi: 10.1016/j.