Cooper M L, Blasdel G G
J Comp Neurol. 1980 Sep 1;193(1):237-53. doi: 10.1002/cne.901930116.
In Siamese cats, many ganglion cell fibers from the temporal retina misproject to the contralateral hemisphere; as a result, each lateral geniculate nucleus contains an abnormally large representation of the ipsilateral visual field. The manner in which the visual cortex processes this aberrant visual information has been examined in several previous studies. In some Siamese cats, the region of the 17/18 border was found to contain an extensive, systematic map of the ipsilateral field, while in other animals no such map was found, and the 17/18 border appeared to represent the zero meridian of azimuth (as in normal cats). These results have led to the suggestion that there are two distinct types of Siamese cat ("Boston" and "Midwestern") which can be distinguished on the basis of cortical topography and the anatomical organization oif the geniculocortical pathway. In the present study, we have recorded from four Siamese cats in order to examine the visual field map in the region of the 17/18 border; in each cat we recorded at anterior coronal levels corresponding to the representation of the lower visual field, and also at more posterior levels near the horizontal meridian representation. In all of the animals we found that the anterior penetrations (corresponding to mean receptive field elevations inferior to -7 degrees) yielded 15-20 degrees of ipsilateral field representation at the 17/18 border; however, the posterior, horizontal meridian penetrations (with mean elevations from +1 degrees to -4 degrees) showed excursions of only about 5 degrees into the ipsilateral field. This large difference in the representation of azimuth was not due to rotation of the eyes during our recording sessions. The finding of appreciable differences in the amount of ipsilateral field represented at different anterior-posterior levels of the same animal might lead to the suggestion that there are not two distinct populations (or types) of Siamese cat with regard to the cortical map of the ipsilateral field. Rather, we raise the possibility that Siamese cats form one population in which there is a continuous variation in the extent of ipsilateral field represented in the cortex.
在暹罗猫中，许多来自颞侧视网膜的神经节细胞纤维错误投射到对侧半球；结果，每个外侧膝状体核包含同侧视野的异常大的表征。在先前的几项研究中已经检查了视觉皮层处理这种异常视觉信息的方式。在一些暹罗猫中，发现17/18边界区域包含同侧视野的广泛、系统的图谱，而在其他动物中未发现这样的图谱，并且17/18边界似乎代表方位角的零度子午线（如在正常猫中）。这些结果表明，有两种不同类型的暹罗猫（“波士顿”和“中西部”），可以根据皮层地形和膝状体皮质通路的解剖组织来区分。在本研究中，我们记录了四只暹罗猫，以检查17/18边界区域的视野图谱；在每只猫中，我们在对应于下视野表征的前冠状水平以及更靠近水平子午线表征的更后水平进行记录。在所有动物中，我们发现前侧穿透（对应于平均感受野高度低于-7度）在17/18边界处产生15-20度的同侧视野表征；然而，后侧的水平子午线穿透（平均高度从+1度到-4度）仅显示约5度进入同侧视野。在我们的记录过程中，方位表征的这种巨大差异不是由于眼睛的转动。在同一动物的不同前后水平上同侧视野表征量存在明显差异这一发现可能表明，就同侧视野的皮层图谱而言，不存在两种不同的暹罗猫群体（或类型）。相反，我们提出一种可能性，即暹罗猫形成一个群体，其中皮层中同侧视野表征的范围存在连续变化。
