Chronic ear infections resulting in a conductive hearing loss (CHL) during development can produce long-term deficits in auditory functions, including those involved with binaural hearing. These include impairment in locating sounds in space, detecting sounds in noisy environments, as well as acquisition of speech and language- all tasks that require the proper integration of information from both ears. In particular, the cue to sound location, which include interaural time (ITD) and level (ILD) difference cues, rely heavily on the proper input of sound information from both ears. Since CHL can attenuate and delay incoming sounds, the cues to sound location can thus be effectively altered. The presence of a CHL during developmental sensitive periods early in life may result in the binaural auditory system adapting to altered binaural cues to location instead of the normal cues, thus providing a possible basis for the persistent spatial hearing problems observed clinically in children. The exact mechanism underlying these persistent effects, however, is not entirely known. Several animal studies have attempted to elucidate the central mechanisms in the developing auditory system, yet few have comprehensively examined the long-term behavioral consequences of early CHL, and none have fully examined its effects on neural information processing of cues to sound location. Therefore, the main goal of this research is to understand the effects of early CHL on (1) behavioral sound localization ability and (2) information processing by neurons sensitive to sound location. Towards these goals, the Specific Aims of the proposed research are to (1) assess behavioral sound localization ability in adult guinea pigs reared with a unilateral CHL and (2) to evaluate the information processing capabilities of neurons in the inferior colliculus (IC) in the same animals reared with a unilateral CHL. Experiments will integrate both behavior and in vivo electrophysiological techniques to jointly assess the effects of early CHL on the binaural auditory system. We hypothesize that early CHL will result in persistent sound localization deficits relative to normal control animals, as well as an impairment in neural information processing of the ILD cue to sound location. In general, we expect greater behavioral deficits to be associated with a reduction in ILD information processing, and that this may provide a possible basis for the persistent spatial hearing deficits observed in children who experienced chronic ear infections early in development. The proposed work is specifically designed to support the mission of NIDCD by advancing the basic understanding of the developing binaural auditory system with clinical relevance to childhood hearing disorders.
Children who experience early conductive hearing loss (CHL) due to recurring ear infections often have persistent problems with spatial hearing, resulting in speech and language deficits. Basic studies of the mammalian binaural auditory pathway will assess the role of early acoustic experience on the developing system, with a particular emphasis on the role of altered inputs. A thorough understanding of normal and abnormal development will facilitate the design of new and better ways to identify, prevent, and possibly to treat early-onset hearing loss.
