Department of Psychology, School of Philosophy, Psychology and Language Sciences, The University of Edinburgh, Edinburgh, UK; Department of Psychology, University of York, Heslington, UK.
York NeuroImaging Centre, The Biocentre, York Science Park, Heslington, UK.
Cortex. 2022 Oct;155:277-286. doi: 10.1016/j.cortex.2022.07.012. Epub 2022 Aug 11.
Braille reading and other tactile discrimination tasks recruit the visual cortex of both blind and normally sighted individuals undergoing short-term visual deprivation. Prior functional magnetic resonance imaging (fMRI) work in patient 'S', a visually impaired adult with the rare ability to read both highly magnified print visually and Braille by touch, found that foveal representations of S's visual cortex were recruited during tactile perception, whereas peripheral regions were recruited during visual perception. Here, we test the causal nature of tactile responses in the visual cortex of S by combining tactile and visual psychophysics with repetitive transcranial magnetic stimulation. First, we replicate the previous fMRI findings in S. Second, we demonstrate that transient disruption of S's foveal visual cortex has no measurable impact on S's tactile processing performance compared to that of healthy controls - a pattern not predicted by the fMRI results. Third, stimulation of foveal visual cortex maximally disrupted visual processing performance in both S and controls, suggesting the possibility of preserved visual processing within S's foveal representation. Finally, stimulation of somatosensory cortex induced the expected disruption to tactile processing performance in both S and controls. These data suggest that tactile responses in S's foveal representation reflect unmasking of latent connections between visual and somatosensory cortices and not behaviourally relevant cross-modal plasticity. Unlike studies in congenitally blind individuals, it is possible that the absence of complete visual loss in S has limited the degree of causally impactful cross-modal reorganisation.
盲人和正常视力的人在接受短期视觉剥夺后，盲文阅读和其他触觉辨别任务都会募集他们的视觉皮层。先前对患者“S”（一位具有罕见能力的视力受损成年人，能够通过触摸既阅读高度放大的印刷品，又阅读盲文）的功能磁共振成像（fMRI）研究发现，S 的视觉皮层的中央凹区域在触觉感知过程中被募集，而外围区域在视觉感知过程中被募集。在这里，我们通过结合触觉和视觉心理物理学以及重复经颅磁刺激来测试 S 的视觉皮层中触觉反应的因果性质。首先，我们复制了 S 中的先前 fMRI 发现。其次，我们证明与健康对照组相比，暂时破坏 S 的中央凹视觉皮层对 S 的触觉处理性能没有可测量的影响——这一模式与 fMRI 结果不一致。第三，刺激 S 和对照组的中央凹视觉皮层最大程度地破坏了视觉处理性能，这表明 S 的中央凹表示中可能存在保留的视觉处理。最后，刺激躯体感觉皮层在 S 和对照组中都引起了预期的触觉处理性能中断。这些数据表明，S 的中央凹表示中的触觉反应反映了视觉和躯体感觉皮层之间潜在连接的去掩蔽，而不是与行为相关的跨模态可塑性。与先天性盲人的研究不同，S 中没有完全的视力丧失可能限制了跨模态重新组织的因果影响程度。
