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Noelle Stiles, Jeiran Coupan, Negin Nadvar, Hossein Ameri, James Weiland, Vivek Patel, Yonggang Shi; Neuroimaging in the Blind with Retinal Prostheses: Does Sensory Reorganization During Blindness Limit Visual Restoration?. Journal of Vision 2020;20(11):892. https://doi.org/10.1167/jov.20.11.892.
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Argus II retinal prostheses restore limited visual perception to the blind by stimulating still viable cells in the eye with an implanted device; nevertheless, the patient outcomes can be quite variable. Therefore, we are studying the factors that could be limiting patient rehabilitation and long-term outcomes. In particular, the senses reorganize during blindness, allowing for tactile information to be processed in visual brain regions. We are investigating whether this sensory reorganization prevents the normal processing of visual information once retinal prostheses are implanted.
Argus II patients (N=6) and blind controls (N=5) performed tactile shape and roughness tasks in a Siemens 3T MRI scanner. Four of these Argus II patients also performed psychophysical tasks outside the scanner.
On average the six Argus II post-implantation patients had tactile incursion of early visual cortex after partial visual restoration, implying that visual cortex is not fully reclaimed for visual processing alone following visual restoration.
Four of the Argus II post-implantation patients with data from psychophysical tasks, showed a significant anti-correlation between their behavioral Argus II visual shape matching performance (outside the scanner), and the amount of tactile repurposing of visual cortex (tactile-only fMRI task). Effectively, the patients that are the most functional with the Argus II visual prosthesis had the least amount of tactile activation (reorganization) of visual cortex.
The Argus II patient fMRI results imply that partial visual restoration does not completely reverse sensory reorganization from blindness. Instead, restored vision seems to co-exist with crossmodal processing in primary visual cortex.
Furthermore, a preliminary correlation analysis indicates that this reorganization may be maladaptive to the rehabilitation of visual perception. If sensory reorganization limits visual restoration, patient outcomes may be improved with training that aims to limit reorganization of the senses during blindness, as well as reverses it after visual restoration.
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