INSERM, U1028, CNRS, UMR5292, Lyon Neuroscience Research Center, ImpAct Team Bron, France ; Mouvement et Handicap, Hospices Civils de Lyon, Inserm et Université de Lyon Bron, France.
Front Hum Neurosci. 2013 Jul 25;7:399. doi: 10.3389/fnhum.2013.00399. eCollection 2013.
Optic ataxia is a component of Balint's syndrome and is a disorder that results from damage to the posterior parietal cortex (PPC) leading to deficits in reaching and grasping objects presented in the visual field opposite to the damaged hemisphere. It is also often the case that Balint's syndrome is accompanied by visual field defects due to the proximity of parietal and occipital cortices and also due to the subcortical pathway relaying visual information from the retina to the visual cortex passing underneath the parietal cortex. The presence of primary visual defects such as hemianopia often prevents clinicians from diagnosing higher-level visual deficits such as optic ataxia; the patient cannot reach to targets he/she cannot see. Here, we show that through the use of a paradigm that takes advantage of remapping mechanisms, we were able to observe optic ataxia in the blind field. We measured reach endpoints of a patient presenting with left optic ataxia as well as a quadrantanopia in the left lower visual field in eye-static and eye-dynamic conditions. In static conditions, we first asked the patient to reach to targets viewed in her non-optic ataxic intact right visual field (fixating on the left of the target array). In this case, the patient showed undershoots equivalent to controls. Next, we asked her to reach to (the same) targets viewed in the upper left optic ataxic but intact visual field (fixating to the right of the target array). The undershooting pattern increased greatly, consistent with unilateral left optic ataxia. In dynamic conditions, we asked her to view targets in her good (right lower) visual field before reorienting her line of sight to the opposite side, causing the internal representation of the target to be updated into the opposite (ataxic) blind visual field. The patient then reached to the remembered (and updated) location of the target. We found errors typical of optic ataxia for reaches guided toward the quadrantanopic field. This confirmed that reaching errors depended on the updated internal representation of the target and not on where the target was viewed initially. In both the patient and the controls, the updating of target location was partial, with reaching errors observed subsequent to an eye movement made from left to right fixation positions being intermediate between the left and right static conditions. Thus, using this remapping paradigm, we were able to observe optic ataxia in the blind field. In conclusion, this remapping paradigm would allow clinicians to test for visuo-manual transformation deficits (optic ataxia) even when it is associated with hemianopia.
视动失调是巴林特综合征的一个组成部分，是由于后顶叶皮层（PPC）损伤导致的一种障碍，表现为对视野中受损半球对侧呈现的物体进行伸手和抓握的能力受损。此外，由于顶叶和枕叶皮质相邻，以及将视网膜的视觉信息传递到视觉皮层的皮质下通路位于顶叶下方，因此视动失调通常还伴有视野缺损。由于初级视觉缺陷（如偏盲）的存在，临床医生常常无法诊断出更高水平的视觉缺陷，如视动失调；患者无法伸手去够他们看不见的目标。在这里，我们通过使用一种利用重映射机制的范例，成功地观察到了盲视野中的视动失调。我们测量了一位左侧视动失调和左侧下视野象限盲的患者在眼静态和眼动态条件下的伸手终点。在静态条件下，我们首先要求患者伸手去够她非视动失调的健全右侧视野中看到的目标（注视目标数组的左侧）。在这种情况下，患者的伸手距离与对照组相当。接下来，我们要求她伸手去够（相同的）目标，这些目标在左上视动失调但健全的视野中（注视目标数组的右侧）。伸手距离大大增加，与单侧左侧视动失调一致。在动态条件下，我们要求她先观看她的健侧（右下）视野中的目标，然后重新将视线转向另一侧，使目标的内部表象更新到对侧（失调）的盲视野中。然后，患者伸手去够目标的记忆（和更新）位置。我们发现，对于朝向象限盲视野的伸手，出现了典型的视动失调错误。这证实了伸手错误取决于目标的更新内部表象，而不是目标最初的观察位置。在患者和对照组中，目标位置的更新都是部分的，从左侧到右侧注视位置的眼动后，伸手错误介于左侧和右侧静态条件之间。因此，通过使用这种重映射范例，我们能够在盲视野中观察到视动失调。总之，这种重映射范例将允许临床医生在与偏盲相关联的情况下，测试视动转换障碍（视动失调）。
