Làdavas E, di Pellegrino G, Farnè A, Zeloni G
University of Bologna, Department of Psychology, Bologna, 40127, Italy.
J Cogn Neurosci. 1998 Sep;10(5):581-9. doi: 10.1162/089892998562988.
Current interpretations of extinction suggest that the disorder is due to an unbalanced competition between ipsilesional and contralesional representations of space. The question addressed in this study is whether the competition between left and right representations of space in one sensory modality (i.e., touch) can be reduced or exacerbated by the activation of an intact spatial representation in a different modality that is functionally linked to the damaged representation (i.e., vision). This hypothesis was tested in 10 right-hemisphere lesioned patients who suffered from reliable tactile extinction. We found that a visual stimulus presented near the patient"s ipsilesional hand (i.e., visual peripersonal space) inhibited the processing of a tactile stimulus delivered on the contralesional hand (cross-modal visuotactile extinction) to the same extent as did an ipsilesional tactile stimulation (unimodal tactile extinction). It was also found that a visual stimulus presented near the contralesional hand improved the detection of a tactile stimulus applied to the same hand. In striking contrast, less modulatory effects of vision on touch perception were observed when a visual stimulus was presented far from the space immediately around the patient"s hand (i.e., extrapersonal space). This study clearly demonstrates the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand and corresponding visual receptive fields in the space immediately adjacent to the tactile fields.
目前对消退现象的解释表明，这种障碍是由于同侧和对侧空间表征之间的竞争失衡所致。本研究探讨的问题是，在一种感觉模态（即触觉）中，左右空间表征之间的竞争是否会因激活与受损表征功能相关的另一种模态（即视觉）中的完整空间表征而减弱或加剧。该假设在10名患有可靠触觉消退的右半球损伤患者中进行了测试。我们发现，在患者同侧手附近呈现的视觉刺激（即视觉个人周边空间）抑制对侧手上传递的触觉刺激的处理（跨模态视觉触觉消退）的程度与同侧触觉刺激（单模态触觉消退）相同。还发现，在对侧手附近呈现的视觉刺激提高了施加在同一手上的触觉刺激的检测。与之形成鲜明对比的是，当视觉刺激在远离患者手部周围空间（即个人外部空间）的地方呈现时，观察到视觉对触觉感知的调节作用较小。这项研究清楚地证明了以人类手部为中心的视觉个人周边空间的存在及其对触觉感知的调节作用。通过参考猕猴运动前区和顶叶皮层中双模态神经元的活动来解释这些发现，这些神经元在手上有触觉感受野，在与触觉感受野紧邻的空间中有相应的视觉感受野。
