Plasticity of the auditory cortex and brainstem in surgically induced unilaterally deaf adult humans with and without tinnitus.

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.