PROJECT SUMMARY Even transient developmental hearing loss (HL) can cause lasting deficits to auditory perception, affecting speech and language acquisition and subsequent educational attainment for many children. Although research suggests that developmental HL can impair temporal processing (e.g., amplitude modulation processing), there is evidence that impairments to the perception of the spectral content are closely correlated with speech comprehension. Furthermore, there is evidence that these deficits are due, in part, to a long-lasting reduction in the strength of inhibitory synapses in auditory cortex (AC). Therefore, the goals of this proposal are to assess the impact of developmental HL on a spectral modulation (SM) detection task in gerbils and to identify a causal relationship between perceptual deficits and reductions in GABAB receptor-mediated inhibition in AC. The core hypothesis of this proposal is that developmental HL will cause a reduction in the function of postsynaptic GABAB receptors, thereby impairing AC encoding of spectrally modulated stimuli and leading to SM detection deficits. Two aims test predictions emerging from this hypothesis: Aim 1A will determine the influence of developmental hearing loss on detection of SM stimuli. Gerbils will be reared with bilateral earplugs from P11- 23, a time when AC inhibition is particularly vulnerable. Twelve days after earplug removal, animals will be tested on a SM detection task. SM thresholds will be obtained across 10 days so that perceptual learning and asymptotic performance can be compared between control and HL-reared animals. Aim 1B will determine whether developmental HL impairs AC neuron encoding of SM stimuli using an awake-behaving preparation. AC will be implanted with an electrode array and recordings will be acquired during SM task performance. Neural sensitivity to a range of modulation depths will be measured between normal hearing and HL animals. Aim 2 will test the prediction that reduced functional GABAB receptors in AC contribute to impaired perception of SM after developmental HL. Using a novel AAV vector to express a gerbil-specific GABAB receptor subunit (Gabrb1b) obtained from the recently sequenced gerbil genome in AC after developmental HL. The AAV-Gabrb1b vector will be injected bilaterally into AC after earplug removal. Behavioral testing will then be performed to determine whether normal SM detection thresholds are restored. Together, these aims will advance our understanding of the neural mechanisms underlying perceptual deficits attending developmental HL and identify a path towards developing the first pharmaceutical treatments for its lasting consequences.