The neural architecture of binocular vision
The neural architecture of binocular vision
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作者：
Casagrande, VA;Boyd, JD
图1所示。灵长类左、右眼与右半球的连接示意图。左鼻视网膜和右颞视网膜的中心大细胞(M)、旁细胞(P)和孔细胞(K)视网膜神经节细胞向右侧外侧膝状核（LCN）的不同层发送轴突。每只眼睛的轴突在视网膜位置上终止，使得视网膜(X)上代表视觉空间中同一点的点在每一层中都有记录。视盘（aD）处视网膜失明的所有LCN层均出现间隙。LCN也接受来自其他直接或间接视网膜组织来源的双眼视觉输入，包括前顶盖（PT）、上丘（SC）、双侧旁核（PC）和初级视觉皮层（VI）。LCN M层和P层向Vi的突起分别在iVa层和IV层(3)结束，在某些物种中也分化成眼优势柱。在丛林幼猴和猕猴中，富含细胞色素氧化酶（CO）的斑点（lIIB层中的圆圈）含有较高百分比的单眼细胞。其余层含有高比例的双眼细胞。lIlA层细胞向2和4视觉区投射，lIIC层细胞向V2和颞中视觉区（MT）投射。第六层细胞向LCN投射，第五层细胞向SC和PT投射。右眼单眼驱动的区域显示为白色；左眼单眼驱动的区域显示为灰色；双目驱动的区域被点画。罗马数字指的是皮层。进一步的讨论请参见文本以及卡萨格兰德和Kaa/。亚层，但进一步分为交替柱，接收来自每只眼睛的输入，眼优势（OD）柱（另见图1）。来自K层的输入终止于皮层III层，并在细胞色素氧化酶（CO斑点）染成深色的区域内结束，并在皮层i层内结束。目前，尚不清楚K通路是否也维持皮层的眼隔离，尽管这是可能的，因为CO斑点在OD柱的中心被发现，单个K LGN轴突仅在单个CO斑点内终止。（在猕猴和灌木幼崽的CO斑点中心记录到的较高比例的单眼细胞14,15可能部分反映了这种单眼LGN输入。）虽然眼睛特定的输入可以在第四层内分离，但它们在皮层加工的下一阶段被结合在一起，并且在第四层之外的所有层中都发现了许多双目细胞。16也就是说，虽然LGN和第四层的神经元通常只对一只眼睛的刺激作出反应，但VI的上颗粒层和下颗粒层的神经元可以通过任何一只眼睛驱动。这些双眼细胞中的一些对两眼之间视网膜位置的小水平差异很敏感，这种差异发生在固定平面前面或后面的刺激上，使差异敏感细胞成为编码深度信息的候选细胞。一旦视觉输入在VI中结合，它就会在所有的外视区域内保持在一起，而不管专业化如何。因此，我们有理由认为，对双目视觉和立体视觉至关重要的相互作用是在皮层第六区建立的。
Fig. 1. A schematic diagram of the connections of the left and right eye with the right hemisphere in a primate. ON and OFF centre magnocellular (M), parvocellular (P) and koniocellular (K) retinal ganglion cells from the left nasal retina and right temporal retina send axons to different layers of the right lateral geniculate nucleus (LCN). The axons from each eye terminate retinotopically such that points on the retina (X) that represent the same point in visual space are in register in each layer. A gap appears in all LCN layers where the retina is blind at the optic disc (aD). The LCN also receive binocular visual input from other direct or indirect retinotopically organised sources including the pretectum (PT), the superior colliculus (SC), parabigeminal nucleus (PC) and primary visual cortex (VI). Projections to Vi from the LCN M and P layers end in layers iVa and IV (3, respectively, and are also segregated into ocular dominance columns in some species. In bush babies and macaque monkeys, the cytochrome oxidase (CO) rich blobs (circles in layer lIIB) contain a higher percentage of monocular cells. The remaining layers contain a high percentage of binocular cells. Cells in layer lIlA project to visual areas 2 and 4 and cells in layer lIIC project to V2 and the middle temporal visual area (MT). Cells in layer VI project to the LCN and cells in layer V project to the SC and PT. Areas driven monocularly by the right eye are shown in white; areas driven monocularly by the left eye are shown in grey; areas driven binocularly are stippled. Roman numerals refer to cortical layers. See text and also Casagrande and Kaa/for further discussion. sublayers but further divided into alternating col umns that receive input from each eye, the ocular dominance (OD) columns (see also Fig. 1). Input from the K layers terminates within cortical layer III where it ends within zones which stain darkly for cytochrome oxidase (CO blobs), and within layer I. At present, it is unclear whether the K pathway also maintains ocular segregation in cortex, although this is likely since CO blobs are found in the centres of the OD columns and individual K LGN axons terminate only within a single CO blob12. l3 (The higher percentage of monocular cells recorded within the centres of macaque and bush baby CO blobs14, 15 may, in part, reflect this monocular LGN input.) Although eye-specific inputs can be segregated within layer IV, they are combined at the next stage of cortical processing, and many binocular cells are found in VI in all layers outside of layer IV. 16 That is, while neurons in LGN and layer IV of VI generally respond only to stimulation of one eye, neurons in supra-and infra-granular layers of VI can be driven through either eye. Some of these binocular cells are sensitive to small horizontal disparities in retinal position between the two eyes/7 such disparities occur for stimuli in front of or behind the fixation plane, making disparity-sensitive cells candidates for encoding depth information. Once ocular input is combined in VI it remains together within all extrastriate visual areas regardless of specialisation. Thus, it seems reasonable to propose that interac tions important to binocular vision and stereopsis are set up in cortical area VI.