The hunt for hidden hearing loss—Linking animal and human studies

Abstract

Many otherwise normal-hearing individuals experience listening problems not apparent from their hearing thresholds. Carefully controlled animal studies using invasive techniques in a range of species have established a clear link between exposure to loud sounds and a range of pathologies underlying this hidden hearing loss (HHL), including cochlear synaptopathy and elevated central gain. Despite progress in these pre-clinical models, however, evidence supporting the existence of HHL in humans remains inconclusive. Here, I review studies of animal models of HHL demonstrating evidence consistent with the types of issues reported by humans who experience problems listening in background noise despite having normal to near-normal hearing thresholds. I suggest that the nature of hearing loss reported by humans—often gradual and multi-factorial—requires us to conceptualize HHL as a system-level listening problem, rather than a coding deficit in sensory processing within the inner ear. I hypothesize that listening deficits in HHL arise from the brain’s homeostatic response to altered sensory input modifying total system gain to stabilize long-term neural activity. Few animal studies have approached the problem from this perspective, while homeostatic responses, such as mal-adaptation to the longer-term statistical structure of acoustic environments, are unlikely to be captured by clinical assessments.