Temporal acuity is preserved in the auditory midbrain of aged mice but why hearing preservation matters

Abstract Impaired temporal resolution of the central auditory system has long been suggested to contribute to speech understanding deficits in the elderly. However, it has been difficult to differentiate between direct age-related central deficits and indirect effects of confounding peripheral age-related hearing loss on temporal resolution. To differentiate this, we measured temporal acuity in the inferior colliculus (IC) of aging CBA/J and C57Bl/6 mice, as a model of aging with and without concomitant hearing loss. We used two common measures of auditory temporal processing: gap detection as a measure of temporal fine structure and amplitude-modulated noise as a measure of envelope sensitivity. Importantly, temporal resolution remained precise in the IC of old CBA/J mice when no or only minimal age-related hearing was present. In contrast, temporal sensitivity was indirectly reduced by the presence of age-related hearing loss in aging C57Bl/6 mice, but not by affecting the brainstem precision, but by affecting the signal-to-noise ratio of the neuronal activity. This demonstrates that indirect effects of (detected or undetected) age-related peripheral hearing loss are likely to remain an important factor for temporal processing in aging in comparison to central auditory decline itself. It also draws attention to the issue that differences in ‘near’ or ‘clinically’ normal hearing in aging subjects in comparison to normal hearing young subjects still could have attenuating effects on central auditory neural representations of temporal processing.