Abstract
Purpose: Neuronal reorganization after blindness is of critical interest because it has implications for the rational prescription of artificial vision devices. The purpose of this study was to distinguish the microstructural differences between perinatally blind (PB), acquired blind (AB), and normally sighted controls (SCs) and relate these differences to performance on functional tasks using a sensory substitution device (BrainPort).Methods: We enrolled 52 subjects (PB n = 11; AB n = 35; SC n = 6). All subjects spent 15 h undergoing BrainPort device training. Outcomes of light perception, motion, direction, temporal resolution, grating, and acuity were tested at baseline and after training. Twenty-six of the subjects were scanned with a three Tesla MRI scanner for diffusion tensor imaging (DTI), and with a positron emission tomography (PET) scanner for mapping regional brain glucose consumption during sensory substitution function. Non-parametric models were used to analyze fractional anisotropy (FA; a DTI measure of microstructural integrity) of the brain via region-of-interest (ROI) analysis and tract-based spatial statistics (TBSS).Results: At baseline, all subjects performed all tasks at chance level. After training, light perception, time resolution, location and grating acuity tasks improved significantly for all subject groups. ROI and TBSS analyses of FA maps show areas of statistically significant differences (p ≤ 0.025) in the bilateral optic radiations and some visual association connections between all three groups. No relationship was found between FA and functional performance with the BrainPort.Discussion: All subjects showed performance improvements using the BrainPort irrespective of nature and duration of blindness. Definite brain areas with significant microstructural integrity changes exist among PB, AB, and NC, and these variations are most pronounced in the visual pathways. However, the use of sensory substitution devices is feasible irrespective of microstructural integrity of the primary visual pathways between the eye and the brain. Therefore, tongue based devices devices may be usable for a broad array of non-sighted patients.
Highlights
Retinal implant chips, sensory substitution devices, or gene therapy can provide a state of ultra-low vision to otherwise blind subjects, being able to generate a signal does not ensure the brain will interpret the stimulus appropriately
Definite brain areas with significant microstructural integrity changes exist among perinatally blind (PB), acquired blind (AB), and NC, and these variations are most pronounced in the visual pathways
The results show that the microstructural integrity of acquired blindness falls between those with perinatal blindness and normal vision, and that there was no significant correlation between BrainPort performance and integrity of the visual pathways between the eye and the visual cortex
Summary
Sensory substitution devices, or gene therapy can provide a state of ultra-low vision to otherwise blind subjects, being able to generate a signal does not ensure the brain will interpret the stimulus appropriately. Park et al (2007) confirmed that the white matter tracts corresponding to visual areas of the brains of non-sighted patients were less organized than sighted controls (SCs); Li et al (2013) expanded this finding with a larger number of subjects. Both studies suggest that early visual experience is necessary to develop normal visual networks within the brain, but how the networks atrophy with time and how this affects our ability to restore vision is not yet well understood. A number of Frontiers in Human Neuroscience www.frontiersin.org
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