Fronto-temporal Delta-gamma Imbalance as a Neural Correlate of Hyperacusis in Tinnitus: An Exploratory EEG Study

Abstract

Objective: To identify quantitative electroencephalography (qEEG)-based connectivity alterations associated with hyperacusis using combined subjective-objective diagnostic criteria. Study design: Retrospective case-control study. Setting: Tertiary referral center. Patients: Seventy-four patients with subjective tinnitus were analyzed. Hyperacusis was defined using combined criteria: subjective complaint and uncomfortable loudness levels (UCL) <= 77 dB HL, resulting in 11 patients with hyperacusis. Extreme groups (11 patients with hyperacusis vs. 23 high-tolerance controls with UCL >= 90 dB) were compared. Intervention(s): None (observational study). Main outcome measure(s): Functional connectivity assessed using the phase-locking value (PLV) and weighted phase lag index (wPLI) for delta, theta, alpha, beta, and gamma frequency bands. Results: Patients with hyperacusis exhibited markedly lower UCLs than the full cohort (56.2 +/- 19.0 vs. 82.4 +/- 22.4 dB HL; P = 0.001, d = 1.19). In the extreme-group EEG analysis, right fronto-temporal connectivity showed increased delta PLV (d = 0.88, 95% CI: -0.14 to 1.90, P = 0.021) and decreased gamma PLV (d = -0.69,95% CI: -1.71 to 0.33, P = 0.044; Welch t test). The delta-gamma balance index differed between groups (d = 1.27, 95% CI: 0.25-2.29, P = 0.003, uncorrected). Supplementary wPLI analysis showed similar directional trends for gamma reduction (d = -0.50, P = 0.068) but not for delta increase (d = 0.07), suggesting differential volume conduction effects across frequency bands. However, no connectivity features survived Benjamini-Hochberg FDR correction across the planned comparisons. Conclusions: In this small, exploratory extreme-group study, a right fronto-temporal delta-gamma imbalance emerged as a candidate connectivity signature of objectively verified hyperacusis in tinnitus. The gamma reduction, partially supported by wPLI analysis, represents the more robust finding, while the delta increase warrants cautious interpretation given its absence in wPLI. Because no features survived FDR correction and CIs were wide, the results are preliminary and warrant replication in larger cohorts.