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Antoine Barbot, Michael Melnick, Matthew Cavanaugh, Anasuya Das, Elisha Merriam, David Heeger, Krystel Huxlin; Visual recovery in chronic cortically-blind patients relies on spared cortical activity and increased V1 coverage of the blind field. Journal of Vision 2018;18(10):1074. doi: 10.1167/18.10.1074.
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© ARVO (1962-2015); The Authors (2016-present)
The primary visual cortex (V1) is the major cortical relay of visual information from the retino-geniculate pathway to higher-level, extrastriate areas. V1 damage causes profound, contralateral, homonymous visual-field defects termed cortical blindness (CB). Although perceptual training can recover some visual functions within the blind field of CB patients, the efficiency and limits of visual rehabilitation are constrained by our poor understanding of the neural mechanisms underlying such recovery. Here, we measured visual field sensitivity and cortical activity using Humphrey (luminance detection) perimetry and functional magnetic resonance imaging (fMRI), respectively, in 9 CB individuals prior and following training-induced recovery of global motion and/or static orientation discrimination. Prior to training, visual stimulation of regions with behaviorally normal visual sensitivity generated strong fMRI activity in spared early visual cortex of the damaged hemispheres. Surprisingly, substantial cortical activity was observed upon stimulation of perimetrically blind-field regions. Such brain activity patterns were not observed in control subjects with artificial scotomas, suggesting cortical reorganization of the chronically-damaged visual system. Moreover, we found a direct correlation between the strength of pre-training V1/V2 activity over blind-field regions and the magnitude of training-induced improvement in visual sensitivity at these blind-field locations. No further change in BOLD signal coherence or amplitude was observed following training. However, CB patients exhibited increased V1 coverage of the blind field, consistent with stronger evoked responses and improved luminance-detection sensitivity within the blind field following training. Our results show for the first time that in chronic CB patients, spared pre-training fMRI activity within the blind field can predict areas amenable for training-induced visual restoration. Additionally, training-induced recovery in visual field sensitivity was associated with increased V1 coverage of the blind field. These findings lead us to hypothesize that training recovers vision primarily by enhancing sensory read-out efficiency at blind-field locations represented by strong pre-training V1/V2 activity.
Meeting abstract presented at VSS 2018
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