Temporal integration in the subcortical auditory system and behavioral evidence of its dysfunction after "temporary" noise-induced hearing loss

How sensory information is processed over time is often conceptualized as a process of temporal integration. Recently, auditory temporal integration has received renewed attention as a potential assay of hidden hearing loss caused by cochlear synaptopathy in rodent and avian studies. How these results relate to human hearing is in question due to a lack of studies in primates, and, more generally, the neural basis of auditory temporal integration is unclear, as most subcortical studies of it have been conducted under anesthesia. We have recently introduced a nonhuman primate (NHP) model which can address translational questions about auditory temporal integration and hidden hearing loss. Thus, in this study, we utilized single-unit recordings and compared derived neurometric measures to psychometric measures of temporal integration in normal hearing NHPs performing a tone-in-noise detection task. We then assessed psychometric measures of temporal integration in NHPs before and after noise exposure. In normal hearing NHPs, cochlear nucleus and inferior colliculus (IC) integration rates were significantly greater than psychometric rates. However, in noise only, [~]25% of IC neurons exhibited similar integration rates to behavior. After noise exposure, psychometric integration was disrupted for brief stimuli presented in quiet, but not in noise. The dynamic range of the psychometric function reliably increased, months after recovery from the noise-induced temporary threshold shift (TTS). Together, these data identify a subcortical neural substrate for temporal integration in noisy environments and suggest that behavioral assays of temporal integration may serve as sensitive indicators of subclinical hearing loss.