Influences of developmental hearing loss on auditory perception and neural coding

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Description (provided by applicant): Many auditory perceptual skills mature over a surprisingly 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 these 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 hearing loss (HL) on central auditory maturation is unsettled. These studies will thus examine functional development in awake animals for the first time, and explore how coding properties are influenced by sensory experience. The central hypothesis of this proposal is that mild to moderate conductive HL during development permanently disrupts coding properties in the auditory cortex, leading to measurable deficits in perceptual performance. There are three related experimental aims. The FIRST AIM will determine whether HL during development disrupts the perceptual abilities of adult animals. Animals will be tested on a psychophysical task known to mature gradually and to be affected by hearing loss in humans: detection of modulation depth in sinusoidally amplitude modulated (SAM) signals. The SECOND AIM will characterize the normal rate of development of neural coding properties in auditory cortex. Those percepts measured behaviorally in Aim 1 will be examined along with other percepts similarly susceptible to developmental perturbation. Single unit recordings will be obtained in awake control animals during the period of development that follows maturation of the cochlea (thus, peripheral processing will not be assessed). The broad goals are to determine whether coding properties mature at different rates, as suggested by human behavioral studies, and to search for neural correlates underlying SAM detection. Finally, the THIRD AIM will assess whether these coding properties are perturbed in a manner that correlates with perceptual deficits in animals reared with conductive HL, measured in Aim 1. Together, these data will provide the first analysis of auditory coding in awake developing animals, and reveal whether HL disrupts both perceptual skills and the coding properties that support them. These studies have direct clinical relevance. By first determining when the central auditory system reaches maturity, it will be possible to determine whether coding properties fail to develop normally, or reach maturity early but begin to regress due to hearing loss. This knowledge will be important in informing clinicians for intervention in cases of early hearing impairment.