Gaymard B, Lynch J, Ploner C J, Condy C, Rivaud-Péchoux S
INSERM U289, Hôpital de la Salpêtrière, 47, Bd de l'Hôpital 75651, Paris cedex 13, France.
Eur J Neurosci. 2003 Apr;17(7):1518-26. doi: 10.1046/j.1460-9568.2003.02570.x.
The monkey lateral intraparietal area (LIP), involved in reflexive shifts of visual attention, has two main oculomotor outputs: towards frontal oculomotor areas and towards the superior colliculus. Recent studies suggest that these two outputs do not carry similar information. Direct LIP-collicular neurons would convey visual signals providing the oculomotor system with on-line visuo-spatial information. Parietal visuo-spatial information regarding internal stimuli would access the brainstem oculomotor circuitry through a parieto-frontal network. Consequently, an interruption of parieto-tectal neurons should affect reflexive saccades towards unpredictable targets and have little or no effect on saccades towards predictable or memorised stimuli. In order to test this hypothesis in humans, we have determined in rhesus monkeys the location of LIP-tectal fibres in the region of the internal capsule, and found that these neurons travel in the most posterior region of the posterior limb of the internal capsule. We have then tested, in seven patients with a small lesion involving this region, several oculomotor paradigms designed to determine the influence of spatial predictability on saccade accuracy and the ability to withhold reflexive saccades. In all patients, saccade accuracy was affected in unpredictable conditions but was normal when target location could be predicted or memorised. Reflexive saccade inhibition was affected only in the three patients in whom the capsular lesion had the most anterior extent. These results therefore support in humans the hypothesis that parieto-tectal neurons (i) transmit an on-line signal that is used by the oculomotor system for reflexive saccade triggering, (ii) are not crucial for the computation of internally guided saccades and (iii) are not crucial for reflexive saccade inhibition.
猴子的外侧顶内区（LIP）参与视觉注意力的反射性转移，有两个主要的动眼输出：朝向额叶动眼区和上丘。最近的研究表明，这两个输出携带的信息并不相似。直接的LIP-上丘神经元会传递视觉信号，为动眼系统提供在线视觉空间信息。关于内部刺激的顶叶视觉空间信息将通过顶叶-额叶网络进入脑干动眼神经回路。因此，顶叶-顶盖神经元的中断应该会影响对不可预测目标的反射性扫视，而对朝向可预测或记忆刺激的扫视影响很小或没有影响。为了在人类中验证这一假设，我们在恒河猴中确定了LIP-顶盖纤维在内囊区域的位置，发现这些神经元走行在内囊后肢的最后部区域。然后，我们对7名涉及该区域的小病灶患者进行了测试，采用了几种动眼范式来确定空间可预测性对扫视准确性的影响以及抑制反射性扫视的能力。在所有患者中，在不可预测的情况下扫视准确性受到影响，但当目标位置可以预测或记忆时则正常。只有在囊部病变范围最靠前的3名患者中，反射性扫视抑制受到影响。因此，这些结果在人类中支持了以下假设：顶叶-顶盖神经元（i）传递一种在线信号，动眼系统利用该信号触发反射性扫视；（ii）对于内部引导扫视的计算并非至关重要；（iii）对于反射性扫视抑制并非至关重要。
