Authors: Dimitri Brunelle¹
¹University of South Florida
Background: Age-related hearing loss is a progressive sensorineural deterioration impacting one-third of the global population over 65 years old, largely affecting the ability to hear in background noise. The loss of peripheral inputs and senescence-related alterations of central neurotransmission lead to decreased activity in the inferior colliculus (IC), a major midbrain convergence site critical for processing complex sounds. However, how aging affects neural encoding of signal-in-noise within the IC remains unresolved. This study investigated these effects in young and old CBA/CaJ mice.
Method: In vivo extra-cellular electrophysiology was used to measure neuronal population responses in the central nucleus of the IC of 11 young and 15 old CBA/CaJ mice during exposure to tones-in-noise. Tone detection was quantified via a d′ sensitivity index and characterized as excitatory or inhibitory, and temporally categorized into onset or sustained responses across various frequency and SNR conditions.
Results: The old group showed a higher proportion of onset responses compared to the young group (53.1% vs. 48.4%). In young mice, there was a higher proportion of tone detection and greater detection strength across most conditions. Interestingly, while overall detection was lower in older mice, specific units that remained robust detectors in the aged group exhibited larger inhibitory-sustained responses to tones-in-noise compared to their younger counterparts.
Conclusion: These findings suggest that the aging IC contains distinct subpopulations of neurons that preferentially encode different signal-in-noise features. The shift toward onset-dominant responses and altered inhibitory dynamics highlight a reorganization of neural encoding properties that may underlie difficulties in processing speech and other complex sounds in noisy environments.
