Abstract
• The unilaterally deaf (UD) with tinnitus group showed high ipsilateral hemisphere cortical auditory evoked potential amplitude.
• This increased sensor level amplitude was not observed in the UD without tinnitus group.
• UD groups showed increased wave III amplitudes.
Objective: Cortical auditory evoked potentials (CAEPs) and auditory brainstem responses (ABRs) were compared between surgically induced unilaterally deaf (UD) adult humans with tinnitus (UD+T), without tinnitus (UD-T), and with binaurally hearing controls (CO). We hypothesised increased CAEP amplitudes from UD+T individuals, and increased ABR amplitudes from all UD individuals.
Methods: Data were gathered from 34 individuals (8 UD-T, 13 UD+T, 13 CO) using a 64-channel BioSemi device. Stimuli were delivered monaurally at 60 dB nHL. Evoked potential amplitudes and scalp topographies were compared between groups.
Results: Only UD+T individuals showed higher N1 amplitude compared to the controls (1.48 versus 1.04 μV) over the ipsilateral hemisphere (relative to intact ear). Higher ABR wave III/V ratios were revealed in both UD groups (UD-T 0.426 and UD+T 0.317) compared with the CO group (0.213), regardless of channel.
Conclusions: Tinnitus is thought to be a perceptual correlate of deafferentation-induced activity increase within the central auditory system (CAS) and the present findings support this. However, increased CAEP amplitude was observed amongst UD+T individuals, while altered ABR amplitude was observed in all UD listeners, suggesting deafferentation alone is insufficient for tinnitus.
Significance: Deafferentation and associated increased brainstem activity may be necessary but insufficient for triggering tinnitus.