Karnath H O
Department of Neurology, University of Tübingen, Germany.
Philos Trans R Soc Lond B Biol Sci. 1997 Oct 29;352(1360):1411-9. doi: 10.1098/rstb.1997.0127.
Damage to the human parietal cortex leads to disturbances of spatial perception and of motor behaviour. Within the parietal lobe, lesions of the superior and of the inferior lobule induce quite different, characteristic deficits. Patients with inferior (predominantly right) parietal lobe lesions fail to explore the contralesional part of space by eye or limb movements (spatial neglect). In contrast, superior parietal lobe lesions lead to specific impairments of goal-directed movements (optic ataxia). The observations reported in this paper support the view of dissociated functions represented in the inferior and the superior lobule of the human parietal cortex. They suggest that a spatial reference frame for exploratory behaviour is disturbed in patients with neglect. Data from these patients' visual search argue that their failure to explore the contralesional side is due to a disturbed input transformation leading to a deviation of egocentric space representation to the ipsilesional side. Data further show that this deviation follows a rotation around the earth-vertical body axis to the ipsilesional side rather than a translation towards that side. The results are in clear contrast to explanations that assume a lateral gradient ranging from a minimum of exploration in the extreme contralesional to a maximum in the extreme ipsilesional hemispace. Moreover, the failure to orient towards and to explore the contralesional part of space appears to be distinct from those deficits observed once an object of interest has been located and releases reaching. Although patients with neglect exhibit a severe bias of exploratory movements, their hand trajectories to targets in peripersonal space may follow a straight path. This result suggests that (i) exploratory and (ii) goal-directed behaviour in space do not share the same neural control mechanisms. Neural representation of space in the inferior parietal lobule seems to serve as a matrix for spatial exploration and for orienting in space but not for visuomotor processes involved in reaching for objects. Disturbances of such processes rather appear to be prominent in patients with more superior parietal lobe lesions and optic ataxia.
人类顶叶皮质受损会导致空间感知和运动行为障碍。在顶叶内，上小叶和下小叶的损伤会引发截然不同的典型缺陷。下（主要是右侧）顶叶病变的患者无法通过眼睛或肢体运动探索对侧空间（空间忽视）。相比之下，上顶叶病变会导致目标导向运动的特定损伤（视觉性共济失调）。本文报告的观察结果支持了人类顶叶皮质下小叶和上小叶功能分离的观点。这些结果表明，忽视患者探索行为的空间参照系受到了干扰。来自这些患者视觉搜索的数据表明，他们未能探索对侧空间是由于输入转换受到干扰，导致以自我为中心的空间表征向同侧偏移。数据还进一步表明，这种偏移是围绕身体垂直轴旋转至同侧，而非向同侧平移。这些结果与以下解释形成鲜明对比：即假设存在一个从极端对侧的最小探索到极端同侧半空间的最大探索的横向梯度。此外，无法朝向和探索对侧空间似乎与一旦找到感兴趣的物体并开始伸手抓取时所观察到的缺陷不同。尽管忽视患者在探索运动方面存在严重偏差，但他们伸向个人空间内目标的手部轨迹可能是直线路径。这一结果表明：（i）空间中的探索行为和（ii）目标导向行为并不共享相同的神经控制机制。下顶叶小叶中的空间神经表征似乎充当空间探索和空间定向的基质，但不参与伸手抓取物体所涉及的视觉运动过程。此类过程的干扰在患有更严重上顶叶病变和视觉性共济失调的患者中似乎更为突出。
