Berman N E, Grant S
Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City 66160.
Vis Neurosci. 1992 Jul;9(1):1-19. doi: 10.1017/s0952523800006337.
The callosal connections between visual cortical areas 17 and 18 in adult normally pigmented and "Boston" Siamese cats were studied using degeneration methods, and by transport of WGA-HRP combined with electrophysiological mapping. In normal cats, over 90% of callosal neurons were located in the supragranular layers. The supragranular callosal cell zone spanned the area 17/18 border and extended, on average, some 2-3 mm into both areas to occupy a territory which was roughly co-extensive with the distribution of callosal terminations in these areas. The region of the visual field adjoining the vertical meridian that was represented by neurons in the supragranular callosal cell zone was shown to increase systematically with decreasing visual elevation. Thus, close to the area centralis, receptive-field centers recorded from within this zone extended only up to 5 deg into the contralateral hemifield but at elevations of -10 deg and -40 deg they extended as far as 8 deg and 14 deg, respectively, into this hemifield. This suggests an element of visual non-correspondence in the callosal pathway between these cortical areas, which may be an essential substrate for "coarse" stereopsis at the visual midline. In the Siamese cats, the callosal cell and termination zones in areas 17 and 18 were expanded in width compared to the normal animals, but the major components were less robust. The area 17/18 border was often devoid of callosal axons and, in particular, the number of supragranular layer neurons participating in the pathway were drastically reduced, to only about 25% of those found in the normally pigmented adults. The callosal zones contained representations of the contralateral and ipsilateral hemifields that were roughly mirror-symmetric about the vertical meridian, and both hemifield representations increased with decreasing visual elevation. The extent and severity of the anomalies observed were similar across individual cats, regardless of whether a strabismus was also present. The callosal pathway between these visual cortical areas in the Siamese cat has been considered "silent," since nearly all neurons within its territory are activated only by the contralateral eye. The paucity of supragranular pyramidal neurons involved in the pathway may explain this silence.
采用变性方法、WGA-HRP转运结合电生理图谱技术，对成年正常毛色和“波士顿”暹罗猫视皮层17区和18区之间的胼胝体连接进行了研究。在正常猫中，超过90%的胼胝体神经元位于颗粒上层。颗粒上层的胼胝体细胞区跨越17/18区边界，平均向两个区域延伸约2 - 3毫米，占据一个与这些区域中胼胝体终末分布大致相同的区域。由颗粒上层胼胝体细胞区的神经元所代表的邻近视网膜垂直子午线的视野区域，显示出随着视觉高度降低而系统性增加。因此，在中央凹附近，从该区域记录到的感受野中心仅向对侧半视野延伸5度，但在 - 10度和 - 40度的高度时，它们分别向该半视野延伸8度和14度。这表明在这些皮层区域之间的胼胝体通路中存在视觉非对应元素，这可能是视觉中线处“粗略”立体视觉的重要基础。在暹罗猫中，与正常动物相比，17区和18区的胼胝体细胞区和终末区宽度增加，但主要成分不那么明显。17/18区边界常常没有胼胝体轴突，特别是参与该通路的颗粒上层神经元数量大幅减少，仅为正常毛色成年猫中发现数量的约25%。胼胝体区包含对侧和同侧半视野的表征，它们大致关于垂直子午线呈镜像对称，并且两个半视野表征都随着视觉高度降低而增加。无论是否存在斜视，在个体猫中观察到的异常程度和严重性相似。暹罗猫这些视皮层区域之间的胼胝体通路被认为是“沉默的”，因为其区域内几乎所有神经元仅由对侧眼激活。参与该通路的颗粒上层锥体神经元数量稀少可能解释了这种沉默现象。
