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Antoine Barbot; Pre-training cortical activity preserved after V1 damage predicts sites of training-induced visual recovery. Journal of Vision 2017;17(15):17. doi: 10.1167/17.15.17.
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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). Perceptual training can recover some visual functions within the blind field of CB patients. However, the efficiency and limits of visual rehabilitation are constrained by our poor understanding of the neural mechanisms underlying training-induced visual recovery. Here, we measured visual sensitivity and cortical activity using Humphrey perimetry and functional magnetic resonance imaging (fMRI), respectively, in 9 CB individuals before and after training-induced visual recovery of global motion and/or static orientation discrimination.
Prior to training, fMRI activity in spared early visual cortex of the damaged hemispheres was seen upon stimulation of regions with behaviorally normal visual sensitivity, as well as following stimulation of perimetrically blind regions of the visual field. In fact, training-induced improvement in visual sensitivity occurred in blind-field regions with stronger pre-training activity. Notably, no further increase in BOLD signal coherence or amplitude occurred in these areas following training.
Our results show for the first time that locations of training-induced visual restoration in CB can be predicted from pre-training fMRI activity. Visual training does not significantly alter retinotopic organization in early visual cortex of chronic CB patients. Instead, we hypothesize that training may enhance sensory read-out efficiency for blind-field locations represented by strong pre-training activity in spared regions of V1 and extrastriate cortex.
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