Galletti Claudio, Kutz Dieter F, Gamberini Michela, Breveglieri Rossella, Fattori Patrizia
Dipartimento di Fisiologia Umana e Generale, Università di Bologna, 40127 Bologna, Italy.
Exp Brain Res. 2003 Nov;153(2):158-70. doi: 10.1007/s00221-003-1589-z. Epub 2003 Sep 27.
The medial parieto-occipital cortex is a central node in the dorsomedial visual stream. Recent physiological studies in the macaque monkey have demonstrated that the medial parieto-occipital cortex contains two areas, the visual area V6 and the visuomotor area V6A. Area V6 is a retinotopically organized visual area that receives form and motion information directly from V1 and is heavily connected with the other areas of the dorsal visual stream, including V6A. Area V6A is a bimodal visual/somatosensory area that elaborates visual information such as form, motion and space suitable for the control of both reaching and grasping movements. Somatosensory and skeletomotor activities in V6A affect the upper limbs and involve both the transport phase of reaching and grasping movements. Finally, V6A is strongly and reciprocally connected with the dorsal premotor cortex controlling arm movements. The picture emerging from these data is that the medial parieto-occipital cortex is well equipped to control both proximal and distal movements in the online visuomotor guidance of prehension. In agreement with this view, selective V6A lesions in monkey produce misreaching and misgrasping with the arm contralateral to the lesion in visually guided movements. These deficits are similar to those observed in optic ataxia patients and suggest that human and monkey superior parietal lobules are homologous structures, and that optic ataxia syndrome is the result of the lesion of a 'human' area V6A.
内侧顶枕叶皮质是背内侧视觉通路的一个核心节点。最近对猕猴的生理学研究表明，内侧顶枕叶皮质包含两个区域，即视觉区域V6和视觉运动区域V6A。V6区是一个按视网膜拓扑结构组织的视觉区域，它直接从V1接收形状和运动信息，并与背侧视觉通路的其他区域紧密相连，包括V6A。V6A区是一个双模态视觉/体感区域，它处理诸如形状、运动和空间等视觉信息，以适应对伸手和抓握动作的控制。V6A区的体感和骨骼运动活动影响上肢，涉及伸手和抓握动作的运输阶段。最后，V6A与控制手臂运动的背侧运动前皮质有强烈的双向连接。从这些数据中浮现出的情况是，内侧顶枕叶皮质在在线视觉运动引导的抓握动作中，具备很好地控制近端和远端运动的能力。与这一观点一致的是，猴子身上V6A区的选择性损伤会导致在视觉引导的动作中，与损伤对侧的手臂出现伸手和抓握失误。这些缺陷与在视觉性共济失调患者中观察到的缺陷相似，这表明人类和猴子的顶上小叶是同源结构，并且视觉性共济失调综合征是“人类”V6A区损伤的结果。
