Grant: Project Grant

In Canada, hearing impairment is the most common sensory disability in adults (affecting 26% of those >45 years old) and deafness is the most common birth defect. Cochlear implants are extremely useful tools in providing auditory sensations to the profoundly deaf and have restored hearing to over 1 million people worldwide. The use of cochlear implants in the profoundly deaf makes human speech comprehension possible. In hearing subjects, acoustic input shapes the development of auditory cortex of the brain. However, in deaf individuals the auditory cortex has no acoustic input. Other senses, such as vision and touch, exploit the unused "deaf" region of cortex for their own purposes. This commonly results in enhanced visual or tactile abilities reported in the deaf. However, if the dormant auditory system is then activated by a cochlear implant, how does "deaf" auditory cortex respond? Does all of "deaf" auditory cortex begin to process sound? Does the visual or tactile processing that invaded "deaf" auditory cortex retreat? Does each auditory cortical area begin to perform the same functions identified in a hearing subject? By better understanding the plastic properties of the brain following cochlear implant, it will be possible to develop implantation strategies to better exploit the plasticity of the brain and improve cochlear implant efficacy and hearing restoration success. The greatest benefit of cochlear prosthetics has been found in young children. Therefore, in the proposed studies, cochlear prosthetics will be implanted in young subjects. We will examine auditory cortical function in the congenitally-deaf cat (the only natural model for human congenital deafness) following cochlear implant. The results from these studies will be directly applicable to clinical studies investigating functional outcomes of cochlear implants in children.