A common tenet of neuroscience is that a brain deprived of stimulation has the ability and tendency to re-organize. That is, intact sensory modalities (e.g., hearing, vision) can recruit the cortices of deprived modalities-known as cross-modal re-organization. A naturally occurring form of sensory deprivation in which cross-modal re-organization has been shown to occur is deafness. In fact, several studies have demonstrated convincing evidence in both animals and humans that the visual system can recruit the auditory cortex in deafness. In contrast, relatively few investigations have shown cross-modal recruitment of the auditory cortex by the somatosensory system in deaf animals and humans. Cochlear implants (CI) are devices that provide access to sound for the auditory system by electrically stimulating the VIII nerve. These devices have proven to be beneficial to many deaf adults and children, with many achieving high levels of behavioral proficiency (e.g., speech perception). On the other hand, some children do not have a great deal of success with CIs. Furthermore, factors such as age of implantation, device programming, and consistency of use have only been able to explain some of the variation in behavioral performance in CI children. However, recent studies have revealed that the degree of cross-modal re-organization between the visual and auditory systems exhibited by adults with CIs is correlated with behavioral performance in these individuals. Due to the high degree of plasticity in the developing brain and because cross-modal re-organization appears to have bearing on behavioral outcomes, it is reasonable to believe that cross-modal re-organization could occur and negatively affect functional performance in children with CIs. No study, to our knowledge, has been done to investigate somatosensory-to-auditory (SS-A) cross-modal re-organization in children with CIs. However, because the somatosensory and auditory systems are responsive to virtually the same physical phenomena (i.e., mechanical pressure in the form of oscillations) in overlapping frequency ranges, it is highly plausible that SS-A cross-modal re-organization could occur in an auditorily deprived system. That is, the auditory system is primed to process somatosensory stimuli, maybe even more so than visual stimuli in some areas of the cortex. If SS-A cross-modal re-organization is occurring in CI children, it may be adversely affecting their behavioral performance. Thus, we propose a study with the following aims: 1) To examine somatosensory-to-auditory cross-modal reorganization using high-density EEG in children with cochlear implants;2) To examine the relationship between somatosensory-to-auditory cross-modal re-organization and functional performance (speech perception) in children with cochlear implants. We hypothesize that high-density EEG and current source reconstruction of cortical activity will reveal SS-A cross-modal re- organization in children with CIs, and that these findings will be negatively correlated with behavioral outcome in these children. Understanding and being able to harness cortical plasticity in children with CIs is not only a recent focus of neuroscientific research, but also represents a worthy endeavor that could lead to improved clinical treatment and management for these patients.
While many children with cochlear implants exhibit functional speech perception performance at, or above, expectation level, others do not. Poor performance often occurs despite an early age of implantation, appropriate device settings, and consistent device use. Studies aimed at elucidating the details of this variability in behavioral performance have only been partially successful. Mounting evidence suggests that the maturation and plasticity of the cerebral cortex may play a significant role in predicting behavioral performance in children with cochlear implants. For instance, it appears that a sensory system that experiences deprivation has the tendency to re-organize. This re-organization can occur by the recruitment of deprived sensory areas by intact modalities (i.e., cross-modal re-organization). Thus, the current study aims to investigate whether the auditory cortex is recruited by the somatosensory system in deaf children who use cochlear implants, and whether the degree of cross-modal re- organization is related to the variability in these children's functional speech and language abilities.
|Sharma, Anu; Campbell, Julia; Cardon, Garrett (2015) Developmental and cross-modal plasticity in deafness: evidence from the P1 and N1 event related potentials in cochlear implanted children. Int J Psychophysiol 95:135-44|