The effects of aging on auditory cortical function

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Age-related hearing loss is a prominent deficit, afflicting approximately half of the geriatric population. In many cases, the person may have no deficits in detecting sounds, but nonetheless suffers from a reduced ability to understand speech, particularly in a noisy environment. While rodent models have shown that there are a variety of age-related changes throughout the auditory neuraxis, far fewer studies have investigated the effects at the cortical level. Here I review recent evidence from a non-human primate model of age-related hearing loss at the level of the core (primary auditory cortex, A1) and belt (caudolateral field, CL) in young and aged animals with normal detection thresholds. The findings are that there is an increase in both the spontaneous and driven activity, an increase in spatial tuning, and a reduction in the temporal fidelity of the response in aged animals. These results are consistent with an age-related imbalance of excitation and inhibition in the auditory cortex. These spatial and temporal processing deficits could underlie the major complaint of geriatrics, that it is difficult to understand speech in noise.HighlightsA major deficit in age-related hearing loss is the ability to understand speech in noise.Neuronal responses in aged macaque monkeys with normal audiograms show increase spontaneous and evoked firing rates.These aged monkey neurons do not show a sharpening of spatial tuning between cortical areas A1 and CL.These aged monkey neurons shift in the population coding strategy from a temporal to a firing rate code.These central changes could underlie the perceptual deficits seen in geriatric populations.

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