Central gain in aging, tinnitus, and temporary hearing loss

Abstract

The nervous system adapts in many ways to changes in the statistics of the inputs it receives. An example of such plasticity observed in animal models is that central auditory neurons tend to retain their driven firing rate outputs despite reductions in cochlear input due to hearing loss or deafferentation. The perceptual consequences of such “central gain” are unknown; pathological versions of such gain are often hypothesized to underlie tinnitus and hyperacusis. To investigate central gain in humans, we designed an electroencephalogram (EEG)-based paradigm that concurrently elicits robust separable responses from different levels of the auditory pathway. Using this measure, we find that cortical responses are relatively invariant despite a large monotonic decrease in auditory nerve responses with age, and that this central gain is also associated with perceptual deficits in co-modulation processing. We then applied the same measures to a cohort of individuals with persistent tinnitus and to a third cohort where a week-long monaural conductive hearing loss was induced using silicone earplugs. Overall, our results suggest that central gain is ubiquitous in response to reduced peripheral input and may affect auditory scene analysis, but does not in itself account for tinnitus perception.

Cross-species experiments reveal widespread cochlear neural damage in normal hearing

“…However, central gain, known to occur as a compensatory mechanism, can serve to resist this reduction and help maintain or even enhance the wave V amplitude. Indeed, data in animal models 52 and preliminary data from human subjects 53 suggest that such compensatory central gain is ubiquitous in young and middle-aged individuals. Thus, purely from an assay-design perspective, the normalization is likely to be beneficial in mitigating the influence of extraneous variables such as head size and tissue geometry 13 for the human subject groups, and thus adopted in this study.…”