Title: Cortical Neuroplasticity and Re-organization in Hearing Loss: Effects of Treatment with Cochlear Implants and Hearing Aids
A basic tenet of neuroplasticity is that the brain will re-organize following sensory deprivation. Sensory deprivation appears to tax the brain by changing its normal resource allocation. Adults and children with hearing loss who receive intervention with hearing aids and cochlear implants provide a platform to examine the trajectories and characteristics of deprivation-induced and experience-dependent plasticity in the central auditory system. We review the evidence for sensitive periods for central development in cochlear-implanted children. Compensation for the deleterious effects of hearing loss also include alterations in cortical functional dynamics such as engagement of additional or alternative cortical networks for listening to degraded auditory input. High-density EEG experiments suggest that hearing loss results in significant changes in neural resource allocation, reflecting patterns of increased listening effort and decreased cognitive reserve that may be associated with dementia-related cognitive decline in hearing loss. Cross-modal plasticity is another form of cortical re-organization associated with hearing loss. Deaf animals show recruitment of higher-order auditory cortical areas, by visual and somatosensory modalities resulting in enhanced processing capabilities for the recruiting modality. Our experiments in human subjects show evidence of recruitment of higher-order auditory cortical areas by visual and somatosensory modalities in developmental and age-related hearing loss. Cross-modal plasticity appears to be related to difficulties in speech-in-noise perception and cognitive processing, and may be reversed by intervention with hearing aids and/or cochlear implants. A better understanding of the cortical re-organization that accompanies hearing loss may allow us to incorporate improvements in the design of prostheses to allow them to better accommodate altered cortical processing. Overall, it appears that the functional activation of cognitive circuitry resulting from cortical reorganization in hearing loss is predictive of outcomes after intervention with amplification and/or electrical stimulation.
Dr. Sharma is a Professor of Speech Language and Hearing Science at the University of Colorado, Boulder.
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