Committee on Computational Neuroscience and Department of Neurobiology, University of Chicago, Chicago, Illinois 60637, USA.
J Neurosci. 2010 Feb 10;30(6):1985-93. doi: 10.1523/JNEUROSCI.3258-09.2010.
A fundamental goal of visual neuroscience is to identify the neural pathways representing different image features. It is widely argued that the early stages of these pathways represent linear features of the visual scene and that the nonlinearities necessary to represent complex visual patterns are introduced later in cortex. We tested this by comparing the responses of subcortical and cortical neurons to interference patterns constructed by summing sinusoidal gratings. Although a linear mechanism can detect the component gratings, a nonlinear mechanism is required to detect an interference pattern resulting from their sum. Consistent with in vitro retinal ganglion cell recordings, we found that interference patterns are represented subcortically by cat LGN Y-cells, but not X-cells. Linear and nonlinear tuning properties of LGN Y-cells were then characterized and compared quantitatively with those of cortical area 18 neurons responsive to interference patterns. This comparison revealed a high degree of similarity between the two neural populations, including the following: (1) the representation of similar spatial frequencies in both their linear and nonlinear responses, (2) comparable orientation selectivity for the high spatial frequency carrier of interference patterns, and (3) the same difference in their temporal frequency selectivity for drifting gratings versus the envelope of interference patterns. The present findings demonstrate that the nonlinear subcortical Y-cell pathway represents complex visual patterns and likely underlies cortical responses to interference patterns. We suggest that linear and nonlinear mechanisms important for encoding visual scenes emerge in parallel through distinct pathways originating at the retina.
视觉神经科学的一个基本目标是确定表示不同图像特征的神经通路。人们普遍认为，这些通路的早期阶段代表了视觉场景的线性特征，而代表复杂视觉模式所需的非线性特征则是在皮质中引入的。我们通过比较皮层下和皮层神经元对由正弦光栅叠加而成的干扰图案的反应来检验这一点。虽然线性机制可以检测到组成光栅，但需要非线性机制来检测它们的总和产生的干扰图案。与体外视网膜神经节细胞记录一致，我们发现，猫外侧膝状体 Y 细胞在皮层下表示干扰图案，但 X 细胞不表示。然后对 LGN Y 细胞的线性和非线性调谐特性进行了表征，并与对干扰图案有反应的皮层 18 区神经元进行了定量比较。这种比较揭示了这两个神经群体之间存在高度的相似性，包括以下几点：（1）在它们的线性和非线性反应中表示相似的空间频率，（2）对干扰图案的高空间频率载波的可比较的方向选择性，以及（3）它们对运动光栅的时间频率选择性与干扰图案包络的差异相同。本研究结果表明，非线性皮层下 Y 细胞通路表示复杂的视觉模式，可能是皮质对干扰模式反应的基础。我们认为，对于编码视觉场景很重要的线性和非线性机制是通过起源于视网膜的不同通路平行出现的。
