Abstract
Background: Auditory deprivation alters cortical and subcortical brain regions, primarily linked to auditory and language processing, resulting in behavioral consequences. Neuroimaging studies have reported various degrees of structural changes, yet multiple variables in deafness profiles need to be considered for proper interpretation of results. To date, many inconsistencies are reported in the gray and white matter alterations following early profound deafness. The purpose of this study was to provide the first systematic review synthesizing gray and white matter changes in deaf individuals.Methods: We conducted a systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement in 27 studies comprising 626 deaf individuals.Results: Evidence shows that auditory deprivation significantly alters the white matter across the primary and secondary auditory cortices. The most consistent alteration across studies was in the bilateral superior temporal gyri. Furthermore, reductions in the fractional anisotropy of white matter fibers comprising in inferior fronto-occipital fasciculus, the superior longitudinal fasciculus, and the subcortical auditory pathway are reported. The reviewed studies also suggest that gray and white matter integrity is sensitive to early sign language acquisition, attenuating the effect of auditory deprivation on neurocognitive development.Conclusions: These findings suggest that understanding cortical reorganization through gray and white matter changes in auditory and non-auditory areas is an important factor in the development of auditory rehabilitation strategies in the deaf population.
Highlights
Neuroplasticity is an intrinsic property of the brain (Dennis et al, 2013) and refers to the brain’s ability to reorganize itself in response to learning and the environmental interactions throughout life (Pascual-Leone et al, 2005)
The present review identified three studies (Allen et al, 2008, 2013; Olulade et al, 2014) that directly compared the brain anatomy of deaf native signers with hearing native signers
Deaf native signers present specific brain differences in regions involved in auditory and language processing and executive functions, and in visual, motor/sensorimotor, and multisensory integrative areas. These findings suggest that early auditory deprivation leads to specific brain changes according to the means of communication
Summary
Neuroplasticity is an intrinsic property of the brain (Dennis et al, 2013) and refers to the brain’s ability to reorganize itself in response to learning and the environmental interactions throughout life (Pascual-Leone et al, 2005). Ontogenetic events support the development of the brain through neurogenesis, axonal and dendritic growth, synaptogenesis, synaptic pruning, and myelination (Anderson et al, 2014). These events are highly interdependent, such that perturbation in one specific area of development can have long-term effects on the brain’s structural and functional integrity (Grantham-McGregor et al, 2007). Brain regions associated with primary functions such as perception (e.g., vision and audition) and gross motor abilities mature first and are followed by areas supporting spatial orientation and language development; brain areas involved in executive function, attention, and motor coordination appear to mature last (Gogtay et al, 2004; Grantham-McGregor et al, 2007). The purpose of this study was to provide the first systematic review synthesizing gray and white matter changes in deaf individuals
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