Somatosensory Cross-Modal Reorganization in Children with Cochlear Implants

Background: In cross-modal reorganization, a well-known phenomenon that occurs in sensory deprivation, intact sensory modalities can recruit and repurpose cortices of deprived modalities. Cross-modal reorganization has been linked to behavioral outcomes in deaf, cochlear-implanted adults. However, there have been no efforts to directly investigate these phenomena in deaf children who receive cochlear implants, even though cross-modal reorganization could potentially shed light on the variability in speech and language outcomes observed in this population. Purpose: The current study included the following aims: 1) To characterize maturation of cortical somatosensory evoked potentials using high-density EEG in normal hearing children, for use in comparison with children with cochlear implants; 2) To examine somatosensory-to-auditory cross-modal reorganization using high-density EEG in children with cochlear implants; 3) To investigate possible correlations between somatosensory-to-auditory cross-modal reorganization and speech perception in children with cochlear implants. We hypothesized that high-density EEG and estimation of the sources of cortical activity would reveal somatosensory cross-modal reorganization in children with CIs, and that these findings would be correlated with behavioral outcomes in these children. Methods: Cortical somatosensory evoked potentials (CSEP) were recorded in response to vibrotactile stimulation of the right index finger in 5-19 year old children with normal hearing (NH) and cochlear implants (CI). Developmental changes were investigated by comparing CSEP latency and amplitude and cortical source estimates across age. Finally, results from a measure of speech perception in noise were correlated with CSEP responses in children with cochlear implants. Results: Waveform morphology and cortical activation were stable across age in the NH group, though latency and amplitude comparisons across age revealed some developmental patterns for the NH children. CI children showed larger amplitudes and shorter latencies for some CSEP components, along with activation of auditory cortical areas in response to vibrotactile stimulation, suggestive of somatosensory cross-modal recruitment. CSEP waveform components were correlated with behavioral performance on a clinical measure of speech perception in background noise for CI children. Conclusions: Overall, our data are suggestive of somatosensory cross-modal reorganization in children with cochlear implants, which may have bearing on their speech perception performance with these devices. Our findings indicate that somatosensory cross-modal reorganization may be a source of variability in CI outcomes, which deserves further investigation

Somatosensory Cross-Modal Reorganization in Adults With Age-Related, Early-Stage Hearing Loss

Under conditions of profound sensory deprivation, the brain has the propensity to reorganize. For example, intact sensory modalities often recruit deficient modalities’ cortices for neural processing. This process is known as cross-modal reorganization and has been shown in congenitally and profoundly deaf patients. However, much less is known about cross-modal cortical reorganization in persons with less severe cases of age-related hearing loss (ARHL), even though such cases are far more common. Thus, we investigated cross-modal reorganization between the auditory and somatosensory modalities in older adults with normal hearing (NH) and mild-moderate ARHL in response to vibrotactile stimulation using high density electroencephalography (EEG). Results showed activation of the somatosensory cortices in adults with NH as well as those with hearing loss (HL). However, adults with mild-moderate ARHL also showed robust activation of auditory cortical regions in response to somatosensory stimulation. Neurophysiologic data exhibited significant correlations with speech perception in noise outcomes suggesting that the degree of cross-modal reorganization may be associated with functional performance. Our study presents the first evidence of somatosensory cross-modal reorganization of the auditory cortex in adults with early-stage, mild-moderate ARHL. Our findings suggest that even mild levels of ARHL associated with communication difficulty result in fundamental cortical changes

Structural Covariance of Sensory Networks, the Cerebellum, and Amygdala in Autism Spectrum Disorder

Sensory dysfunction is a core symptom of autism spectrum disorder (ASD), and abnormalities with sensory responsivity and processing can be extremely debilitating to ASD patients and their families. However, relatively little is known about the underlying neuroanatomical and neurophysiological factors that lead to sensory abnormalities in ASD. Investigation into these aspects of ASD could lead to significant advancements in our general knowledge about ASD, as well as provide targets for treatment and inform diagnostic procedures. Thus, the current study aimed to measure the covariation of volumes of brain structures (i.e., structural magnetic resonance imaging) that may be involved in abnormal sensory processing, in order to infer connectivity of these brain regions. Specifically, we quantified the structural covariation of sensory-related cerebral cortical structures, in addition to the cerebellum and amygdala by computing partial correlations between the structural volumes of these structures. These analyses were performed in participants with ASD (n = 36), as well as typically developing peers (n = 32). Results showed decreased structural covariation between sensory-related cortical structures, especially between the left and right cerebral hemispheres, in participants with ASD. In contrast, these same participants presented with increased structural covariation of structures in the right cerebral hemisphere. Additionally, sensory-related cerebral structures exhibited decreased structural covariation with functionally identified cerebellar networks. Also, the left amygdala showed significantly increased structural covariation with cerebral structures related to visual processing. Taken together, these results may suggest several patterns of altered connectivity both within and between cerebral cortices and other brain structures that may be related to sensory processing