An electrophysiological approach to tinnitus interpretation

Introduction: Serotonin seems to play a central role in tinnitus. The intensity dependence of auditory evoked potential (IDAP) is considered an index of central serotonergic activity in the auditory cortex. The higher the steepness of the N1/P2 component amplitude-stimulus function slope (N1/P2 ASF slope as calculated by IDAP), the lower the central serotonergic activity. Similarly, the N1 amplitude-stimulus function slope (N1 ASF slope) was investigated. Auditory brainstem responses (ABR) examine the auditory system functionality from the periphery and through the brainstem, where serotonergic projections have been identified. Objectives: Assessing whether tinnitus perception neurotransmitters activity inbalance could be investigated by an electrophysiological approach. Materials and Methods: Ten normoacousic tinnitus patients and 14 healthy controls were included in the study. Subjects underwent EEG (IDAP) recording, ABR recording and psychometric questionnaires administration. Results: N1/P2 ASF slope and N1ASF slope tended to have a greater steepness in patients. N1ASF slope was significantly correlated with ABR wave V and interpeak III-V latencies in patients. ABR wave V and interpeak III-V latencies were significantly longer in patients than in controls. Conclusion: N1/P2 ASF slope, N1 ASF slope and ABR components appear to be useful electrophysiologic methods to study possible functional alterations related to the serotonergic activity.