Abstract
Sensory substitution devices (SSDs) are providing new ways for improving or replacing sensory abilities that have been lost due to disease or injury, and at the same time offer unprecedented opportunities to address how the nervous system could lead to an augmentation of its capacities. In this work we have evaluated a color-blind subject using a new visual-to-auditory SSD device called “Eyeborg”, that allows colors to be perceived as sounds. We used a combination of neuroimaging techniques including Functional Magnetic Resonance Imaging (fMRI), Diffusion Tensor Imaging (DTI) and proton Magnetic Resonance Spectroscopy (1H-MRS) to study potential brain plasticity in this subject. Our results suggest that after 8 years of continuous use of this device there could be significant adaptive and compensatory changes within the brain. In particular, we found changes in functional neural patterns, structural connectivity and cortical topography at the visual and auditive cortex of the Eyeborg user in comparison with a control population. Although at the moment we cannot claim that the continuous use of the Eyeborg is the only reason for these findings, our results may shed further light on potential brain changes associated with the use of other SSDs. This could help to better understand how the brain adapts to several pathologies and uncover adaptive resources such as cross-modal representations. We expect that the precise understanding of these changes will have clear implications for rehabilitative training, device development and for more efficient programs for people with disabilities.
Highlights
Neuroplasticity is an intrinsic property of the brain, which allows us to adapt to environmental pressures, physiologic changes and experiences by dynamic shifts in the strength of pre-existing connections or by establishing new networks in response to changes in afferent inputs or efferent demands (Pascual-Leone et al, 2005)
The color-selective activation in the control group was situated in occipital, temporal, parietal and frontal cortex. These areas were located in: (1) occipital lobe; (2) temporal lobe related to object and face recognition (BA37), language and auditory processing (BA21, BA22, BA42), memory (BA38) and high level object representation; and (3) parietal lobe related to stimulation and texture discrimination tasks (BA40), visuo-motor coordination (BA7, BA6, BA4), and somatosensory functions (BA2); and (4) prefrontal cortex, related with executive functions (BA9, BA10, BA11, 46) and semantic tasks (45, 44)
When we compared the fiber tracts between the Eyeborg user and the controls we found higher fractional anisotropy value (FA) values in the Eyeborg user in the corpus callosum (CC), and in both inferior longitudinal fasciculus (ILF) and in both inferior fronto-occipital fasciculus (IFOF)
Summary
Neuroplasticity is an intrinsic property of the brain, which allows us to adapt to environmental pressures, physiologic changes and experiences by dynamic shifts in the strength of pre-existing connections or by establishing new networks in response to changes in afferent inputs or efferent demands (Pascual-Leone et al, 2005). Hearing colors modifies the brain by our experiences and developmental constraints. Such ability can be viewed as adaptivewhen associated with a gain in function (Cohen et al, 1997) or as maladaptive when linked to negative consequences such as loss of function or increased injury (Nudo, 2006). The understanding of the nature of these changes is important in terms of establishing the brain’s true adaptive potential and in guiding future rehabilitation strategies (Merabet and Pascual-Leone, 2010)
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