Your Brain on TMJ
TMJ and other chronic pain disorders are associated with altered brain structure and function. A paper by Moayedi and colleagues expands knowledge in this area by describing the changes in white matter tract anatomy in TMJ patients compared with healthy controls (healthy people without TMJ). 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 brain regions.
The investigators 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 sent to the thalamus and other regions of the brain. They found that people with TMJ had decreased white matter signals in the trigeminal nerve and that this decrease depended upon how long a patient had TMJ—the longer one had suffered from TMJ, the less white matter was in the nerve. It not is clear whether and how this finding is directly related to the TMJ 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 TMJ patients’ experience. The research team 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’ TMJ pain or unpleasantness ratings, thus suggesting a link between altered structure and symptoms. Previous work from the same group of researchers showed altered gray matter in similar parts of the brain in people with TMJ; the current study provides more details on the structural brain changes that occur with TMJ.
Finally, Moayedi and colleagues reported altered connectivity to prefrontal regions of the brain, including a decrease in connectivity to the dorsolateral prefrontal cortex (DLPFC) and increased connectivity to the frontopolar cortex (FPC) in TMJ 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 TMJ 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 TMJ, future research will need to clarify the relationship of brain function and structure and TMJ 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.