Influence of moderate hearing loss on auditory perception & cortical processing

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PROJECT SUMMARY Many auditory perceptual skills mature over a long time course (in humans), well into the teenage years. If hearing is disrupted during development, there may be long-lasting deficits in auditory perception and language acquisition. Surprisingly, maturation of the auditory coding properties that support late-emerging perceptual skills are largely unknown; what little we do know is based solely on recordings from anesthetized animals. This is also why our understanding of the effect of mild to moderate hearing loss on central auditory maturation is unsettled. To address these issues, I will examine functional development in awake animals for the first time, and explore how auditory coding properties are influenced by sensory experience. The central hypothesis is that moderate hearing loss during development disrupts coding properties in the auditory cortex (ACx), leading to measurable deficits in auditory perceptual performance. There are three related aims: AIM 1 will determine whether developmental conductive hearing loss disrupts the perceptual abilities of adult gerbils. Animals will be tested on two tasks that, in humans, are known to have different rates of maturation and to be affected by hearing loss. These include detection of sinusoidal amplitude (sAM) and frequency modulated (sFM) signals. AIM 2 will determine whether training on an auditory task during juvenile development can rescue normal perceptual behavior in animals reared with conductive hearing loss. AIM 3 will characterize the normal rate of development of neural coding properties underlying the percepts examined in Aim 1, and will assess whether these coding properties are perturbed in a manner that correlates with perceptual deficits examined in AIM 1. Single unit recordings will be obtained from the ACx of awake animals during the period of development that follows cochlear maturation. The broad goals are to determine whether coding properties mature at different rates, as suggested by behavioral studies, and to determine whether sAM or sFM coding is vulnerable to early hearing loss. Together, these data will provide the first analysis of auditory coding in awake developing animals, and reveal whether moderate hearing loss disrupts both perceptual skills and the coding properties that support them.