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Liana Brown, Jody Culham, Greg Kroliczak, Melvyn Goodale; Improved blindsight near the hand is associated with increased fMRI activation in the superior parietal-occipital cortex. Journal of Vision 2008;8(6):52. doi: 10.1167/8.6.52.
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Recently we reported the case of MB, a young man showing improved residual visual processing in his blind (upper left) field when he placed his ipsilateral hand near the target object. We argued that placing the hand near the target allowed the target to fall within the receptive field of visual-tactile bimodal cells linked to the hand, and that their recruitment bolstered visual processing. Here we use fMRI to examine this possibility further. If visual processing is improved in the hand-near condition because bimodal cells are recruited, then we may observe that brain areas thought to contain populations of bimodal cells may be more active when the hand is near, rather than far from, the target. We asked MB to either reach or grasp for targets presented briefly either in his good upper-right visual field or his blind upper-left visual field under two conditions. In the hand-near condition, his hand was placed next to the target location, and in the hand-far condition, his hand rested away from the target location. We found that when targets were presented in his blind field, the right superior parieto-occipital (SPOC) area was more active in the hand-near condition than in the hand-far condition. Previous studies have also found that SPOC is sensitive to the proximity of the target to the body, as it shows greater activation for targets within reach than beyond reach. Furthermore, previous single-cell recordings in monkeys and imaging studies in humans show that the region around the parietal-occipital sulcus is multimodal; it responds both to visual and tactile information. Therefore, SPOC appears to be recruited more robustly when a hand is near a visual target, and its recruitment may help explain the hand-near improvements we observed for MB's blind grip-size scaling.
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