The Effects of Aging on Auditory Perception in CBA/CaJ Mice
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In this dissertation, I examined the effects of age-related hearing loss (ARHL) on the detection of pure tones and ultrasonic vocalizations (USVs) in male and female CBA/CaJ mice. I used cross-sectional and accelerated longitudinal designs and operant conditioning procedures with positive reinforcement to show that ARHL affected detection of pure tones and USVs in mice across listening conditions. In experiment 1, I constructed behavioral audiograms for 65 male and female CBA/CaJ mice. Mice experienced decreases in hearing sensitivity across pure tones after 700 days of age. Similar to humans, male and female mice diverge in their hearing abilities for pure tones in the last third of their lifespan, with females having lower thresholds than males. Unlike humans, mice showed sex differences across all frequencies in old age. In the second experiment, I constructed temporal integration functions using thresholds from 36 male and female mice. Mice showed an increase in thresholds for tones shorter than 50 ms, reaching peak performance at shorter durations than other rodent species. Mice lost hearing at similar rates across frequencies and durations. I hypothesized that duration may interact with other acoustic stimulus parameters in the processing of simple and behaviorally relevant signals. In experiment 3, I measured hearing for USVs and pure tones in quiet and white noise listening conditions in 48 male and female mice. Mice had higher thresholds for USVs and pure tones in noise than in quiet. Male mice had consistent hearing sensitivity for several masked USVs across their lifespan, while females showed progressive hearing loss for all stimuli. Overall performance was more variable in the quiet condition than in white noise. I hypothesized that selective auditory attention for USVs may be activated by a mild white noise masker in mice. These dissertation findings highlight the importance of using a wide range of stimuli and a longitudinal design when comparing presbycusis across different species.