Sharpee Tatyana O, Victor Jonathan D
Computational Neurobiology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
J Comput Neurosci. 2009 Apr;26(2):203-18. doi: 10.1007/s10827-008-0107-5. Epub 2008 Aug 5.
The apparent receptive field characteristics of sensory neurons depend on the statistics of the stimulus ensemble--a nonlinear phenomenon often called contextual modulation. Since visual cortical receptive fields determined from simple stimuli typically do not predict responses to complex stimuli, understanding contextual modulation is crucial to understanding responses to natural scenes. To analyze contextual modulation, we examined how apparent receptive fields differ for two stimulus ensembles that are matched in first- and second-order statistics, but differ in their feature content: one ensemble is enriched in elongated contours. To identify systematic trends across the neural population, we used a multidimensional scaling method, the Procrustes transformation. We found that contextual modulation of receptive field components increases with their spatial extent. More surprisingly, we also found that odd-symmetric components change systematically, but even-symmetric components do not. This symmetry dependence suggests that contextual modulation is driven by oriented On/Off dyads, i.e., modulation of the strength of intracortically-generated signals.
感觉神经元明显的感受野特性取决于刺激集合的统计学特征——这是一种常被称为上下文调制的非线性现象。由于从简单刺激确定的视觉皮层感受野通常无法预测对复杂刺激的反应，因此理解上下文调制对于理解对自然场景的反应至关重要。为了分析上下文调制，我们研究了两个在一阶和二阶统计上匹配但特征内容不同的刺激集合的明显感受野如何不同：一个集合富含细长轮廓。为了识别整个神经群体的系统趋势，我们使用了一种多维缩放方法，即正交变换。我们发现感受野成分的上下文调制随着其空间范围的增加而增加。更令人惊讶的是，我们还发现奇对称成分会系统地变化，而偶对称成分则不会。这种对称性依赖性表明上下文调制是由定向的开/关二元组驱动的，即皮层内产生信号强度的调制。
