Superficial and deep white matter brain alterations discriminate tinnitus in older adults.

Subjective tinnitus is the perception of sound in the absence of an external source, with a neurobiological basis that remains poorly understood. Importantly, tinnitus prevalence increases with aging, reaching up to 25 % in adults aged above 65 years. This study examines white matter tract alterations in older adults with tinnitus using diffusion magnetic resonance imaging. The research involved 96 individuals from the Chilean ANDES cohort, including 56 patients with tinnitus and 40 controls. Thirty-six deep white matter (DWM) and 84 superficial white matter (SWM) bundles were segmented. For each bundle, we extracted four diffusion tensor imaging metrics: axial diffusivity (AD), mean diffusivity (MD), radial diffusivity (RD), and fractional anisotropy (FA). With these features, we trained an Extreme Gradient Boosting classifier to predict tinnitus, achieving an AUC of 0.93, highlighting the relevance of AD. Key DWM bundles included the anterior arcuate fasciculus, inferior longitudinal fasciculus, and cingulum short fibers (right hemisphere), and the superior motor thalamic radiation (left hemisphere). Significant SWM bundles in the left hemisphere included the superior parietal, cuneus, lingual, superior temporal, caudal middle frontal, precentral, fusiform, postcentral, supramarginal, rostral middle frontal, and superior frontal regions. Tinnitus patients showed decreased AD, MD, and RD, and increased FA, suggesting microstructural reorganization. These changes may reflect adaptive or maladaptive plasticity. Increased FA could signal compensatory responses, while decreased AD might indicate axonal damage. Meanwhile, the decrease in MD and RD could indicate an enhancement in myelin health. This is the first study to investigate SWM bundle alterations in tinnitus patients.