Martinez-Garcia Marina, Martinez Luis M, Malo Jesús
Instituto de Neurociencias, CSIC, Alicante, Spain.
Image Processing Lab., Universitat de València, València, Spain.
PLoS One. 2017 Jun 22;12(6):e0178345. doi: 10.1371/journal.pone.0178345. eCollection 2017.
Neurons at primary visual cortex (V1) in humans and other species are edge filters organized in orientation maps. In these maps, neurons with similar orientation preference are clustered together in iso-orientation domains. These maps have two fundamental properties: (1) retinotopy, i.e. correspondence between displacements at the image space and displacements at the cortical surface, and (2) a trade-off between good coverage of the visual field with all orientations and continuity of iso-orientation domains in the cortical space. There is an active debate on the origin of these locally continuous maps. While most of the existing descriptions take purely geometric/mechanistic approaches which disregard the network function, a clear exception to this trend in the literature is the original approach of Hyvärinen and Hoyer based on infomax and Topographic Independent Component Analysis (TICA). Although TICA successfully addresses a number of other properties of V1 simple and complex cells, in this work we question the validity of the orientation maps obtained from TICA. We argue that the maps predicted by TICA can be analyzed in the retinal space, and when doing so, it is apparent that they lack the required continuity and retinotopy. Here we show that in the orientation maps reported in the TICA literature it is easy to find examples of violation of the continuity between similarly tuned mechanisms in the retinal space, which suggest a random scrambling incompatible with the maps in primates. The new experiments in the retinal space presented here confirm this guess: TICA basis vectors actually follow a random salt-and-pepper organization back in the image space. Therefore, the interesting clusters found in the TICA topology cannot be interpreted as the actual cortical orientation maps found in cats, primates or humans. In conclusion, Topographic ICA does not reproduce cortical orientation maps.
人类和其他物种初级视觉皮层（V1）中的神经元是在取向图中组织的边缘滤波器。在这些图中，具有相似取向偏好的神经元聚集在等取向域中。这些图具有两个基本属性：（1）视网膜拓扑，即图像空间中的位移与皮质表面位移之间的对应关系，以及（2）在以所有取向良好覆盖视野与皮质空间中等取向域的连续性之间的权衡。关于这些局部连续图的起源存在着激烈的争论。虽然现有的大多数描述采用纯粹的几何/机械方法而忽略了网络功能，但文献中这一趋势的一个明显例外是Hyvärinen和Hoyer基于信息最大化和地形独立成分分析（TICA）的原始方法。尽管TICA成功地解决了V1简单和复杂细胞的许多其他属性，但在这项工作中，我们质疑从TICA获得的取向图的有效性。我们认为，TICA预测的图可以在视网膜空间中进行分析，而这样做时，很明显它们缺乏所需的连续性和视网膜拓扑。在这里我们表明，在TICA文献中报道的取向图中，很容易找到视网膜空间中类似调谐机制之间连续性违反的例子，这表明与灵长类动物的图不兼容的随机加扰。这里在视网膜空间中进行的新实验证实了这一猜测：TICA基向量在图像空间中实际上遵循随机的椒盐组织。因此，在TICA拓扑中发现的有趣聚类不能被解释为在猫、灵长类动物或人类中发现的实际皮质取向图。总之，地形ICA不能再现皮质取向图。
