Payne B R
Department of Anatomy and Neurobiology, Boston University School of Medicine, MA 02118.
Behav Brain Res. 1994 Oct 20;64(1-2):55-64. doi: 10.1016/0166-4328(94)90118-x.
The article summarizes three sets of physiological and anatomical studies carried out to investigate the structural basis of the functional interactions between visual cortical areas 17 and 18 in the two cerebral hemispheres of cats. (1) The visual field representations in the transcallosal sending and receiving zones are defined. (2) The consequences of severing callosal fibers on the visual field representation at the area 17/18 border are described. (3) Lastly, experiments using cooling to reversibly inactive transcallosal inputs are reported. The observations on the transcallosal sending and receiving zones show that callosal connections of area 17 are concerned with a vertical hour-glass shaped region of the visual field centered on the midline, and this region is doubly represented, once in each hemisphere. The zone represents azimuths within +/- 4 degrees of the midline at the 0 degree horizontal meridian, and azimuths out to +/- 15 to +/- 25 degrees at positions distant from the horizontal meridian. The observations suggest that, in addition to interactions between neurons concerned with positions immediately adjacent to the midline, there are positions, especially high and low in the visual field, where interactions can occur between neurons which have receptive fields displaced some distance from the midline. The extent of this double representation is reduced by approximately 2/3 when the corpus callosum is cut. The retention of some bilateral representation in these animals suggests that there are alternate routes for across-the-midline transmission of visual signals. Or, more likely, there are ganglion cells in temporal retina with crossed projections that make significant contributions to the remaining double representation of the visual field. Lastly, the results obtained using cooling inactivation of transcallosal fibers show that many excitatory and inhibitory circuits are under the direct control of transcallosal fibers in the normally functioning brain. These connections appear to be no different from intrinsic connections of area 17, and they undoubtedly contribute to the binding of the two half-field representations, one in each hemisphere, and perceptual unity across the midline.
本文总结了为研究猫的两个大脑半球中视觉皮层17区和18区之间功能相互作用的结构基础而开展的三组生理和解剖学研究。（1）确定了胼胝体传入和传出区域中的视野表征。（2）描述了切断胼胝体纤维对17/18区边界处视野表征的影响。（3）最后，报告了使用冷却使胼胝体传入输入可逆失活的实验。对胼胝体传入和传出区域的观察表明，17区的胼胝体连接与以中线为中心的视野垂直沙漏形区域有关，该区域在每个半球中都有双重表征。该区域在0度水平子午线处代表中线两侧±4度范围内的方位角，在远离水平子午线的位置代表中线两侧±15至±25度范围内的方位角。这些观察结果表明，除了与紧邻中线位置相关的神经元之间的相互作用外，在视野的某些位置，尤其是视野的上部和下部，具有离中线一定距离的感受野的神经元之间也可能发生相互作用。当胼胝体被切断时，这种双重表征的范围大约减少了2/3。这些动物中保留的一些双侧表征表明，存在视觉信号跨中线传输的替代途径。或者，更有可能的是，颞侧视网膜中有交叉投射的神经节细胞对视野剩余的双重表征做出了重要贡献。最后，使用冷却使胼胝体纤维失活获得的结果表明，在正常功能的大脑中，许多兴奋性和抑制性回路受胼胝体纤维的直接控制。这些连接似乎与17区的内在连接没有不同，它们无疑有助于将每个半球中的两个半视野表征结合起来，并实现跨中线的感知统一。
