The long-term goal of this work is to identify neural mechanisms that limit perceptual abilities as a result of developmental hearing loss. In the auditory system, chronic middle ear infections (otitis media) in children result in fluctuating conductive hearing loss (HLC) during development. The duration of hearing loss is correlated with persistent perceptual problems including speech processing deficits. Processing of time-varying auditory signals is particularly vulnerable to early hearing loss. Recent work in an animal model of conductive hearing loss shows that early hearing impairment shifts both synaptic properties and responses to sound in auditory cortex. However, it is unknown how altered synaptic elements shape cortical tuning, or how altered cortical tuning contributes to impaired perception. To address these issues, this project examines the chain of events initiated by hearing loss in order to establish the links between synaptic changes in auditory cortical neurons, their effects on the sound-evoked responses of these neurons, and impaired perception.
Aim 1 will determine response properties that are vulnerable to early hearing loss.
Aim 2 will determine the synaptic mechanisms that shape altered response properties of neurons in auditory cortex.
Aim 3 will identify how cortical responses to auditory stimuli that are altered by hearing loss relate to perceptual impairments. The degree to which early hearing loss causes a simple maturational delay or novel pathology is unknown. Several neural changes due to early hearing loss indicate a delayed maturation of synaptic components and auditory responses. However, temporal response properties in hearing-impaired animals are not uniformly immature, and Aim 1 will identify those elements of time-varying stimuli that are susceptible to the effects of auditory deprivation. In particular, early hearing loss impairs processing of slow but not fast amplitude modulations (AM). However, preliminary data indicate that it may be the rate of the amplitude rise in AM signals, rather than the frequency of the modulations, that elicits abnormal neural responses. This distinction is important: speech is composed of periodic amplitude and frequency modulations with a variety of slow and fast rise times. Studies of dyslexia and specific language impairment indicate that the neural processing of a subset of these speech components is impaired, which has led to directed therapeutic interventions. This proposal will identify which stimulus parameters elicit responses that are altered by early hearing loss. Understanding the neural basis of impairments resulting from chronic conductive hearing loss is a necessary step toward providing targets for intervention and remediation.
In children, chronic middle ear infections (otitis media) that result in fluctuating hearing loss produce persistent deficits in auditory processing abilities, including speech perception. The resulting dysfunction in auditory cortex may play a critical role in these deficits, but the links between synaptic changes in cortex, their effects on cortical sound-evoked responses, and impaired perception are not known. By establishing these links, this work will identify which aspects of auditory signal processing are most at risk from early hearing loss, providing targets for intervention and remediation.