Montreal Neurological Institute, McGill University, Montreal, Canada.
Department of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands.
Neuropsychologia. 2019 May;128:198-203. doi: 10.1016/j.neuropsychologia.2018.06.026. Epub 2018 Jun 30.
Blindsight refers to the ability of some patients with destruction of the primary visual cortex (V1) to respond to stimuli presented in their clinically blind visual field despite lack of visual awareness. Here we tested a rare and well-known patient with blindsight following hemispherectomy, DR, who has had the entire cortex in the right hemisphere removed, and in whom the right superior colliculus is the only post-chiasmatic visual structure remaining intact. Compared to more traditional cases of blindsight after damage confined to V1, the study of blindsight in hemispherectomy has offered the invaluable opportunity to examine directly two outstanding questions: the contribution of the intact hemisphere to visual processing without awareness, and the nature of plastic and compensatory changes in these remaining contralesional visual areas. Population receptive field (pRF) mapping was used to define retinotopic maps, delineate the boundaries between the visual areas, examine changes in the sizes of receptive field centres within each visual area, and their variability as a function of eccentricity. Aside from the dorsal visual areas showing blurred borders between V2d and V3d, not otherwise detected with perimetric mapping, the retinotopic maps of DR did not differ substantially from those of three matched healthy controls. Interestingly, those dorsal compartments showed a significant increase in the RF sizes toward values typical of higher-order processing cortices, while no differences were observed in the corresponding ventral visual areas. Findings showed that whereas receptive field sizes at foveal and parafoveal eccentricities (≤ 4°) were not measurably altered, the pRF size increased by ~ 270% at 4-6° of eccentricity, and the size difference reached ~ 300% between 8° and 10°. We interpret these findings to suggest that an increase in pRF sizes could be indicative of cerebral plasticity involving the retinotopic reorganization of the dorsal visual areas.
盲视是指一些患者在初级视皮层（V1）受损后，尽管缺乏视觉意识，但仍能对临床盲视场中的刺激做出反应。在这里，我们测试了一位罕见的、患有盲视的半球切除术患者 DR，他的右半球整个皮层都被切除了，而右侧上丘是唯一完整的视交叉后视觉结构。与局限于 V1 损伤的传统盲视病例相比，半球切除术盲视的研究提供了一个宝贵的机会，可以直接研究两个突出的问题：完整大脑半球对无意识视觉处理的贡献，以及这些残留对侧视觉区域的可塑性和代偿性变化的性质。利用群体感受野（pRF）映射来定义视网膜映射，描绘视觉区域之间的边界，检查每个视觉区域内感受野中心大小的变化，以及它们随离中心距离的变化。除了背侧视觉区域的 V2d 和 V3d 之间的边界模糊，这在周边视野测量中无法检测到，DR 的视网膜映射与三个匹配的健康对照没有显著差异。有趣的是，那些背侧区域的感受野大小显著增加，达到了更高阶处理皮层的典型值，而对应的腹侧视觉区域则没有差异。研究结果表明，虽然中央和旁中心（≤ 4°）的感受野大小没有明显改变，但在 4-6°的偏心距处 pRF 大小增加了约 270%，在 8-10°的偏心距处大小差异达到了约 300%。我们将这些发现解释为，感受野大小的增加可能表明大脑的可塑性涉及到背侧视觉区域的视网膜映射重组。
