Age-related hearing loss (presbycusis) affects one-third of the world’s population. One hallmark of presbycusis is difficulty hearing in noisy environments. While much focus has been placed on age-related changes to the inner ear, less is known about the age-related changes in the brain that affect auditory processesing. We embarked on rvealing how age changes the processing of sound information in the auditory cortex and what the underlying ciruit changes are with the goal to prevent or reverse these changes. So far our work in mice has shown that auditory cortex contains distinct subpopulations of excitatory neurons that preferentially encode different stimulus features and that aging selectively reduces certain subpopulations. We also found that aging increases correlated activity between neurons and thereby reduces the response diversity in auditory cortex and leads to defecits in sound encoding (Shilling-Scrivo et al. 2021). We then trained mice to detect tones in noise and found that aging reduces the ability to suppress its responses to background noise. This excess activity additionally leads to increased correlations between neurons, reducing the amount of relevant stimulus information in the auditory cortex (Shilling-Scrivo et al. 2022, JHU news). We are now investigating the underlying circuit changes in a mouse model of presbycusis (C57Bl/6 mice) and so far find that auditory cortex cells from aged C57Bl/6J mice have fewer excitatory connections with weaker connection strength. Whereas young adult and aged C57Bl/6J mice have similar amounts of inhibitory connections, the strength of local inhibition is weaker in the aged group. thus our work shows that presbycusis changes excittaory and inhibitory cortical circuits (Xue et al. 2023).