The power of language: Functional brain network topology of deaf and hearing in relation to sign language experience

Abstract

Prolonged auditory sensory deprivation leads to brain reorganization, indicated by functional enhancement in remaining sensory systems, a phenomenon known as cross-modal plasticity.In this study we investigated differences in functional brain network shifts from eyes-closed to eyes-open conditions between deaf and hearing people. Electroencephalography activity was recorded in deaf (N = 71) and hearing people (N = 122) living in rural Africa, which yielded a unique data-set of congenital, pre-lingual and post-lingual deaf people, with a divergent experience in American Sign Language. Functional networks were determined from the synchronization of electroencephalography signals between fourteen electrodes distributed over the scalp. We studied the synchronization between the auditory and visual cortex and performed whole-brain minimum spanning tree analysis based on the phase lag index of functional connectivity. This tree analysis accounts for variations in global network density and allows unbiased characterization of functional network backbones. We found increased functional connectivity between the auditory and visual cortex in deaf people during the eyesclosed condition in both the alpha and beta bands. Furthermore, we found functional network backbone shifts both in deaf and healthy people as they went from eyes-closed to eyes-open conditions. In both the alpha and beta band the deafs' brain showed larger functional backbone-shifts in node strength compared to controls. In the alpha band this shift in network strength differed among deaf participants and depended on type of deafness: congenital, prelingual or post-lingual deafness. In addition, a correlation was found between functional backbone characteristics and experience of sign language. Our study revealed more insights in functional network reorganization specifically due to prolonged lack of auditory input, but might also be helpful for sensory deprivation and cross-modal plasticity in general. Global cortical network reorganization in deaf people supports the plastic capacities of the young brain. The differences between type of deafness stresses that etiology affects functional .

Early Sensory Loss Alters the Dendritic Branching and Spine Density of Supragranular Pyramidal Neurons in Rodent Primary Sensory Cortices

“…There is also a stronger functional connectivity between sensory processing cortices in adults with long-term sensory deprivation compared to normal individuals. For example, human studies revealed a stronger functional connectivity between the auditory, visual, and/or somatosensory in early deaf [electroencephalography: Sinke et al, 2019; functional magnetic resonance imaging (fMRI): Shiell et al, 2015; Bola et al, 2017] and blind people (resting-state fMRI: Pelland et al, 2017; dynamic causal modeling (DCM) of fMRI data: Collignon et al, 2013) and between V1 and S1 in Braille reading blinds (rsfMRI: Liu et al, 2007; DCM: Fujii et al, 2009).…”

MRI-based Measurement of Structural and Functional Connectivity in Health and Disease

“…Thereby it minimizes the sum of the costs of all edges over the set of all possible MSTs that could be constructed from the original graph (Hidalgo et al, 2007). The usefulness of MST analysis has been shown in previous studies on ageing (Boersma et al, 2013;Otte et al, 2015;Smit et al, 2016), multiple sclerosis (Engels et al, 2015;Tewarie et al, 2015b), epilepsy (van Diessen et al, 2016, which we extended with our studies on deafness (Sinke et al, 2019) and stroke (chapter 4). MSTs seem to able to capture similar network characteristics as classical graph analysis, without being biased by the number of nodes and edges (Tewarie et al, 2015a;van Wijk et al, 2010).…”

Resting-state EEG reveals global network deficiency in prelingually deaf children with late cochlear implantation

“…Once this step of artifact rejection had been completed, we then interpolated the rejected electrodes. Furthermore, previous studies have found that using multiple epochs per subject increases the stability of network metrics ( 43 , 61 ). Therefore, to ensure the stability of the results and to exclude the possible influence of the number of epochs per subject on the results, the number of epochs in the present study was set to 72 for all subjects in both the EC and EO conditions.…”

“…There is accumulating evidence that MST analysis can capture subtle changes in brain networks during human development ( 59 , 60 ), and this approach has been used extensively in EEG resting-state data from diverse populations, including people with deafness ( 61 ), autism ( 62 ), Alzheimer's disease ( 63 ), and dyslexia ( 46 ). In a recent EEG resting-state study, MST analysis was used to compare brain network characteristics between deaf and hearing controls in different resting states ( 61 ). The results showed differences in the topological characteristics of brain networks between the deaf group and the hearing group.…”

“…These results suggest that early auditory deprivation may lead to abnormal brain network topological characteristics. Further analysis revealed that the number of years spent on sign language learning was related to characteristics of the brain network, that is, the longer the time spent on sign language learning, the higher the global brain efficiency ( 61 ). Although years of sign language learning were not directly representative of language processing ability, these findings indirectly suggested that changes in individual language levels could be reflected in network characteristics.…”