As of 2010, approximately 25,500 children born with severe to profound hearing loss in the United States have received a cochlear implant. This biomedical device provides access to sound via direct electrical stimulation of the VIII cranial nerve. For children who receive this device, age of implantation has been shown to be critical for appropriate stimulation of central auditory pathways and subsequent development of speech and language skills. However, age at implantation does not entirely predict the level of success in speech and language outcomes, and variability in speech and language skills in cochlear implanted children remains an important focus of research in the literature. Many factors have been shown to be significant in accounting for variability in speech and language performance, including socio-economic status of the family of the child receiving the implant and duration of deafness. Another source of variability in speech perception that has come to the forefront of cochlear implant research in recent years includes cross-modal re-organization of the cortex. When one sensory modality is deprived, another will recruit neurons from the deprived modality to increase function, likely to compensate for the lack of sensory input. Indeed, cases of visual-to-auditory cross-modal re-organization (visual cortical recruitment via auditory cortex) have been found via high-density electroencephalography (EEG) recordings in adults who received cochlear implants;positron emission tomography (PET) imaging has shown similar findings in congenitally deaf children who receive cochlear implants. The first goal of this proposal is to examine visual-to-auditory cross-modal re-organization in children with cochlear implants, but through non-invasive high-density EEG recordings. By presenting visual stimuli to implanted children, visual cortex becomes activated and may be observed as a response in the occipital lobe through topographic scalp maps of mean voltage values for the averaged recording. In implanted subjects, activation of non-visual areas (such as the temporal and parietal lobes) indicates recruitment of non-visual areas to aid in visual processing, indicating the occurrence of cross-modal re-organization. This re-organization may create competition for available resources when the deprived sense (audition) is re-introduced to the brain through a cochlear implant. Along these lines, the literature has shown that greater visual-to-auditory cross- modal re-organization is correlated with poorer speech perception performance in implanted subjects. Thus, the second goal of this proposal is to correlate the extent of visual-to-auditory cross-modal re- organization with speech perception scores with the purpose of determining whether or not cross- modal re-organization is indeed a possible source of variance in speech perception performance for children with cochlear implants.
Not all children with cochlear implants demonstrate optimal speech and language development, and there remains a great deal of variance in speech and language performance to be explained in this population. Visual-to-auditory cross-modal re-organization of the cortex has been shown to negatively correlate with speech perception performance in implanted adults, and cortical studies in implanted children indicate that cross-modal plasticity may predict speech perception performance post-implantation. Thus, the goal of this study is to examine whether visual to auditory cross-modal re-organization in children with cochlear implants may act as another source of variability in speech and language performance.
|Campbell, Julia; Sharma, Anu (2014) Cross-modal re-organization in adults with early stage hearing loss. PLoS One 9:e90594|