Tinnitus with a normal audiogram: physiological evidence for hidden hearing loss and computational model.

Summary

Many tinnitus patients have a normal audiogram, with no direct sign of cochlear damage. In such patients, auditory brainstem responses showed a significantly reduced wave I (generated by primary auditory-nerve fibres) but normal wave V (generated more centrally). That pattern is direct physiological evidence of 'hidden hearing loss', reduced neural output from the cochlea, followed by renormalisation of response magnitude within the brainstem. An established computational model then shows how tinnitus can arise from this homeostatic response to reduced auditory-nerve input, even without elevated hearing thresholds.

Key findings

• Tinnitus patients with normal audiograms show reduced ABR wave I but normal wave V.
• Direct physiological evidence of 'hidden hearing loss': less cochlear neural output without raised thresholds.
• Normal wave V indicates the brainstem has renormalised its response, central gain compensating for reduced input.
• A computational model shows tinnitus can emerge from this homeostatic compensation.