Hyperacusis-associated pathological resting-state brain oscillations in the tinnitus brain: a hyperresponsiveness network with paradoxically inactive auditory cortex.

Although hyperacusis, a hyperresponsiveness to non-noxious auditory stimuli, is a sound-evoked symptom, possible resting-state pathologic oscillations in hyperacusis brain have never been explored. By comparing 17 tinnitus participants with hyperacusis (T+H+) and 17 without hyperacusis (T+H-), we aimed to explore characteristic resting-state cortical activity of hyperacusis. The T+H+ and T+H- groups, strictly matched for all tinnitus sound characteristics to exclude tinnitus-related cortical changes, were compared using resting-state electroencephalography source-localized activity complemented by functional connectivity analyses. Correlation analysis revealed that hyperacusis questionnaire score was positively correlated with the orbitofrontal cortex (OFC) beta power, the right auditory cortex (AC) alpha1 power, and the dorsal anterior cingulate cortex (dACC) beta1 power. Compared to the T+H- group, the T+H+ group demonstrated increased beta power in the dACC and OFC, and increased alpha power in the right AC. Region of interest analyses including 17 normal controls further confirmed that these differences originated solely from relatively increased power of the T+H+ group, not from a relative power decrease of the T+H- group. Also, the T+H+ group showed increased connectivity between the OFC/dACC and the AC as compared to the T+H- group. The beta power increase in the OFC/dACC may indicate increased resting-state vigilance in tinnitus patients with hyperacusis. In addition, increased alpha power in the AC may reflect an adaptive top-down inhibition against sound stimuli probably mediated by the increased beta power of the OFC. The OFC/dACC, also frequently found to be activated in analogous diseases such as allodynia/hyperalgesia, may compose a hyperresponsiveness network.