Neural dynamics in tinnitus: differential effects of hearing status on temporal brain activity variability

Tinnitus, characterized by phantom sound perception, exhibits heterogeneous pathophysiology influenced by hearing status. This study investigated dynamic neural activity patterns in 82 participants: 29 healthy controls (HC), 21 tinnitus patients with normal hearing (G1), and 32 tinnitus patients with hearing impairment (G2). Using resting-state fMRI, we computed dynamic amplitude of low-frequency fluctuation (d-ALFF) and dynamic regional homogeneity (d-ReHo) through sliding-window analyses, measuring temporal variability via coefficient of variation. One-way ANOVAs (covarying age/sex) revealed six d-ALFF clusters showing group differences (voxel p < 0.01, cluster p < 0.05 GRF-corrected). Post-hoc analyses demonstrated that G1 exhibited significantly increased d-ALFF variability versus HC and G2 in cerebellar, fusiform, and occipital regions. Conversely, both patient groups showed reduced d-ALFF variability in frontal clusters versus HC. Negative correlations emerged in G2 between fusiform d-ALFF and tinnitus distress/anxiety, while G1 showed positive correlations between temporal d-ALFF and depression. d-ReHo analysis identified reduced variability in the right anterior cingulate in both patient groups versus HC. These findings highlight distinct neural dynamics: tinnitus with normal hearing involves hypervariability in sensory processing regions, while hearing-impaired tinnitus shows distinct clinical correlations. Reduced activity variability in the superior and middle frontal gyri and reduced temporal synchrony in the anterior cingulate suggest a common tinnitus mechanism irrespective of hearing status.