Changes in gray and white matter in subgroups within the tinnitus population

In this study, we investigated gray and white matter changes in subgroups within the larger tinnitus population related to differences in severity or duration of tinnitus symptoms. Tinnitus is the illusory perception of sound in the absence of an external source, most often experienced as a chronic condition. The psychological reaction to the sound constitutes the severity, or degree of discomfort experienced, and the duration refers to the time since onset of chronic tinnitus. We used voxel- and surface-based morphometry to investigate gray matter changes and diffusion tensor imaging (using fractional anisotropy, or FA, metrics) to assess changes in orientation of white matter tracts, using both whole brain and region of interest analyses. Whole brain analyses revealed decreased cortical thickness in the left parahippocampal gyrus in those with more severe tinnitus compared to a group with a milder reaction, and reduced gray matter volume in left anterior cingulate in those with mild tinnitus compared to a normal hearing control group without tinnitus. In the analysis based on FA, no significant differences were revealed between the subgroups or with respect to control groups in either whole brain or region of interest analyses. Our results suggest that these subgroups within the tinnitus population likely exhibit different anatomical alterations related to the disorder, which may explain the variable findings in the literature, particularly in terms of gray matter.