Williams Patrick E, Shapley Robert M
New York University Center for Neural Science, New York, New York 10003, USA.
J Neurosci. 2007 May 23;27(21):5706-18. doi: 10.1523/JNEUROSCI.4743-06.2007.
While studying the visual response dynamics of neurons in the macaque primary visual cortex (V1), we found a nonlinearity of temporal response that influences the visual functions of V1 neurons. Simple cells were recorded in all layers of V1; the nonlinearity was strongest in neurons located in layer 2/3. We recorded the spike responses to optimal sinusoidal gratings that were displayed for 100 ms, a temporal step response. The step responses were measured at many spatial phases of the grating stimulus. To judge whether simple cell behavior was consistent with linear temporal integration, the decay of the 100 ms step response at the preferred spatial phase was used to predict the step response at the opposite spatial phase. Responses in layers 4B and 4C were mostly consistent with a linear-plus-static-nonlinearity cascade model. However, this was not true in layer 2/3 where most cells had little or no step responses at the opposite spatial phase. Many layer 2/3 cells had transient preferred-phase responses but did not respond at the offset of the opposite-phase stimuli, indicating a dynamic nonlinearity. A different stimulus sequence, rapidly presented random sinusoids, also produced the same effect, with layer 2/3 simple cells exhibiting elevated spike rates in response to stimuli at one spatial phase but not 180 degrees away. The presence of a dynamic nonlinearity in the responses of V1 simple cells indicates that first-order analyses often capture only a fraction of neuronal behavior. The visual implication of our results is that simple cells in layer 2/3 are spatial phase-sensitive detectors that respond to contrast boundaries of one sign but not the opposite.
在研究猕猴初级视觉皮层（V1）中神经元的视觉反应动力学时，我们发现了一种影响V1神经元视觉功能的时间反应非线性。在V1的所有层中记录了简单细胞；这种非线性在位于第2/3层的神经元中最强。我们记录了对显示100毫秒的最佳正弦光栅的尖峰反应，即时间阶跃反应。在光栅刺激的许多空间相位处测量阶跃反应。为了判断简单细胞的行为是否与线性时间积分一致，使用在首选空间相位处100毫秒阶跃反应的衰减来预测相反空间相位处的阶跃反应。第4B层和第4C层中的反应大多与线性加静态非线性级联模型一致。然而，在第2/3层并非如此，其中大多数细胞在相反空间相位处几乎没有或没有阶跃反应。许多第2/3层细胞具有瞬态的首选相位反应，但在相反相位刺激的偏移处没有反应，表明存在动态非线性。另一种刺激序列，即快速呈现的随机正弦波，也产生了相同的效果，第2/3层简单细胞对一个空间相位的刺激表现出较高的尖峰率，但对180度以外的刺激没有反应。V1简单细胞反应中存在动态非线性表明，一阶分析通常只捕捉到了神经元行为的一部分。我们结果的视觉意义在于，第2/3层中的简单细胞是空间相位敏感探测器，对一种符号的对比度边界有反应，而对相反的边界没有反应。
