The Effects of Reversible Hearing Loss on the Development of Auditory Perception and Neural Coding

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 DESCRIPTION (provided by applicant): Childhood hearing loss disrupts central processing of spectral and temporal cues, and may contribute to perceptual deficits, including impaired speech and language processing. Though difficulties can persist even after normal auditory input is restored, earlier restoration is correlated with superior recovery. These findings suggest that there is a critical period of development during which the neural mechanisms subserving auditory processing are particularly vulnerable to sensory perturbations. The key goal of this proposal is to determine whether a brief period of developmental hearing loss disrupts the neural and perceptual detection of amplitude modulation (AM), a temporal cue necessary for speech comprehension and non-human animal communication. The core hypothesis is that transient hearing loss during a critical period disrupts the neural encoding of AM stimuli, thereby producing a perceptual impairment that persists after normal peripheral function is restored. This hypothesis will be explored in detail, with two experimental aims. Specific Aim 1 will determine whether there is a critical period during which temporary hearing loss impairs subsequent AM detection. Sound attenuation will be induced by the insertion of bilateral earplugs at various postnatal ages. After a period of restored auditory input (via earplug removal), animals will be trained and tested on an aversive conditioning paradigm designed to assess amplitude modulation detection capabilities. Behavioral performance will be quantified by calculating correct responses and false alarms. Detection thresholds will be estimated from psychometric functions and compared between earplug-reared animals and normally-reared littermates. These measures will reveal whether there is a critical period during which the maturation of AM detection is sensitive to hearing loss. Specific Aim 2 will examine the impact of temporary, developmental hearing loss on central sensory encoding in auditory cortex of awake-behaving animals performing the AM detection task described in Aim 1. Multi- and single-unit responses will be recorded wirelessly from chronically implanted electrode arrays in left auditory cortex. AM-evoked firing rates and power will be calculated and used to calculate neurometric curves that can be directly compared to behavioral psychometric functions. Additional analyses will assess the relationship between behavior and neural activity on trial-by-trial basis. Results will be compared between earplug-reared and normally-reared animals. The results of this experiment will elucidate whether behavioral deficits arising from developmental hearing loss can be explained by disrupted sensory coding, as is generally assumed, or whether non-sensory (e.g. cognitive) factors contribute to perceptual dysfunction. Together, these findings will reveal whether there is a discrete developmental critical period for the neural representation and perceptual detection of AM. Ultimately, these results may further our understanding of speech and language delays associated with childhood hearing loss, a goal directly relevant to the mission of NIDCD.