Exploratory Functional MRI Assessment of Trigeminal System Activation in Asymptomatic Individuals With Temporomandibular Joint Disc Displacement

BACKGROUND: Temporomandibular disorders appear to involve central sensory processing, including the thalamus and brainstem trigeminal complex. OBJECTIVE: To explore task-based fMRI activity of the trigeminal system in asymptomatic individuals with MRI-confirmed temporomandibular joint disc displacement versus controls. METHODS: Seventeen asymptomatic participants were included: controls without temporomandibular complaints or MRI evidence of disc displacement (Group 1, n = 10) and individuals with disc displacement without pain or functional limitation (Group 2, n = 7). fMRI was acquired during centric-occlusion clenching versus relaxed jaw (block design; cluster-corrected z > 3.1). Activation maps were intersected voxel-wise with trigeminally relevant ROIs of the Adil et al. brainstem atlas. In an exploratory case-level approach, overlap volume, peak z and percentage BOLD signal change were reported per activated ROI; group comparisons were descriptive only. RESULTS: In Group 1, trigeminally relevant activation was limited to the atlas region 'thalamus excluding pulvinar' (substantive in 4/10 controls; bilateral in one; peak z 4.24-5.15; BOLD change 0.79%-1.28%). In Group 2, one participant with right-sided complete anterior disc displacement showed a medullary cluster overlapping the left spinal trigeminal tract (24 voxels, peak z 5.06, 0.95%) and nucleus interpolaris (35 voxels, peak z 5.60, 1.13%), among several adjacent structures; no thalamic activation occurred in this group. No between-group difference was statistically significant. CONCLUSIONS: A medullary activation cluster overlapping the left spinal trigeminal tract and nucleus interpolaris, among several adjacent medullary structures, was observed in one participant with asymptomatic TMJ disc displacement. This single-case, hypothesis-generating observation requires confirmation in larger cohorts using brainstem-optimized fMRI.