Dissecting drivers of maladaptive plasticity in the aging central auditory system

Aging is associated with reduced speech perception in complex environments, even in individuals with normal audiometric thresholds. While peripheral cochlear deficits are well characterized, less is known about how central auditory structures adapt to age-related changes. One proposed mechanism, central gain, reflects compensatory plasticity in the central auditory system following diminished peripheral input. While this phenomenon is increasingly recognized, its physiological and molecular underpinnings remain poorly understood. Here, we investigated age-related changes in central gain using envelope following responses (EFRs) in Mongolian gerbils. We recorded EFRs to amplitude-modulated stimuli designed to differentiate cortical and peripheral neural sources. A central gain index, defined as the ratio of cortical-to-peripheral EFR amplitudes, increased by ∼8 dB in aged animals, despite no change in hearing thresholds. To isolate peripheral and central contributions to gain, we employed two manipulations: permanent threshold shifts via noise exposure and reversible attenuation via earplugging. Both manipulations produced level-dependent increases in central gain, mimicking age-related effects. Notably, central gain returned to baseline following earplug removal, indicating that restoring peripheral input can reverse compensatory gain. Ongoing work aims to link these physiological markers with molecular changes in excitatory–inhibitory balance in the auditory cortex.