Vuilleumier Patrik, Sergent Claire, Schwartz Sophie, Valenza Nathalie, Girardi Michele, Husain Masud, Driver Jon
University Medical Center, Geneva, Switzerland.
J Cogn Neurosci. 2007 Aug;19(8):1388-406. doi: 10.1162/jocn.2007.19.8.1388.
Right hemisphere lesions often lead to severe disorders in spatial awareness and behavior, such as left hemispatial neglect. Neglect involves not only pathological biases in attention and exploration but also deficits in internal representations of space and spatial working memory. Here we designed a new paradigm to test whether one potential component may involve a failure to maintain an updated representation of visual locations across delays when a gaze-shift intervenes. Right hemisphere patients with varying severity of left spatial neglect had to encode a single target location and retain it across an interval of 2 or 3 sec, during which the target was transiently removed, before a subsequent probe appeared for a same/different location judgment. During the delay, gaze could have to shift to either side of the remembered location, or no gaze-shift was required. Patients showed a dramatic loss of memory for target location after shifting gaze to its right (toward their "intact" ipsilesional side), but not after leftward gaze-shifts. Such impairment arose even when the target initially appeared in the right visual field, before being updated leftward due to right gaze, and even when gaze returned to the screen center before the memory probe was presented. These findings indicate that location information may be permanently degraded when the target has to be remapped leftward in gaze-centric representations. Across patients, the location-memory deficit induced by rightward gaze-shifts correlated with left neglect severity on several clinical tests. This paradoxical memory deficit, with worse performance following gaze-shifts to the "intact" side of space, may reflect losses in gaze-centric representations of space that normally remap a remembered location dynamically relative to current gaze. Right gaze-shifts may remap remembered locations leftward, into damaged representations, whereas left gaze-shifts will require remapping rightward, into intact representations. Our findings accord with physiological data on normal remapping mechanisms in the primate brain but demonstrate for the first time their impact on perceptual spatial memory when damaged, while providing new insights into possible components that may contribute to the neglect syndrome.
右半球损伤常常导致空间意识和行为方面的严重障碍，比如左侧半空间忽视。忽视不仅涉及注意力和探索方面的病理性偏差，还包括空间内部表征和空间工作记忆的缺陷。在此，我们设计了一种新的范式，以测试当发生眼跳干预时，一个潜在因素是否可能涉及在延迟期间无法维持视觉位置的更新表征。患有不同严重程度左侧空间忽视的右半球患者必须编码单个目标位置，并在2或3秒的间隔内记住它，在此期间目标会短暂消失，随后会出现一个探测刺激，用于判断目标位置是否相同/不同。在延迟期间，眼睛可能需要看向记忆位置的一侧，或者不需要眼跳。患者在将目光转向右侧（朝向其“完好”的同侧）后，对目标位置的记忆出现了显著丧失，但向左眼跳后则没有。即使目标最初出现在右视野，之后由于向右眼跳而更新到左侧，甚至在呈现记忆探测刺激之前目光又回到屏幕中心时，这种损伤仍然会出现。这些发现表明，当目标必须以注视为中心的表征向左重新映射时，位置信息可能会永久退化。在所有患者中，向右眼跳引起的位置记忆缺陷与多项临床测试中的左侧忽视严重程度相关。这种矛盾的记忆缺陷，即在向空间的“完好”一侧眼跳后表现更差，可能反映了以注视为中心的空间表征的丧失，这种表征通常会相对于当前注视动态地重新映射记忆位置。向右眼跳可能会将记忆位置向左重新映射到受损表征中，而向左眼跳则需要向右重新映射到完好表征中。我们的发现与灵长类动物大脑中正常重新映射机制的生理数据一致，但首次证明了它们在受损时对感知空间记忆的影响，同时为可能导致忽视综合征的潜在因素提供了新的见解。
