Priebe Nicholas J, Lisberger Stephen G, Movshon J Anthony
Department of Physiology, Howard Hughes Medical Institute, W. M. Keck Foundation Center for Integrative Neuroscience, University of California, San Francisco, California 94143, USA.
J Neurosci. 2006 Mar 15;26(11):2941-50. doi: 10.1523/JNEUROSCI.3936-05.2006.
We recorded the responses of direction-selective simple and complex cells in the primary visual cortex (V1) of anesthetized, paralyzed macaque monkeys. When studied with sine-wave gratings, almost all simple cells in V1 had responses that were separable for spatial and temporal frequency: the preferred temporal frequency did not change and preferred speed decreased as a function of the spatial frequency of the grating. As in previous recordings from the middle temporal visual area (MT), approximately one-quarter of V1 complex cells had separable responses to spatial and temporal frequency, and one-quarter were "speed tuned" in the sense that preferred speed did not change as a function of spatial frequency. Half fell between these two extremes. Reducing the contrast of the gratings caused the population of V1 complex cells to become more separable in their tuning for spatial and temporal frequency. Contrast dependence is explained by the contrast gain of the neurons, which was relatively higher for gratings that were either both of high or both of low temporal and spatial frequency. For stimuli that comprised two spatially superimposed sine-wave gratings, the preferred speeds and tuning bandwidths of V1 neurons could be predicted from the sum of the responses to the component gratings presented alone, unlike neurons in MT that showed nonlinear interactions. We conclude that spatiotemporal modulation of contrast gain creates speed tuning from separable inputs in V1 complex cells. Speed tuning in MT could be primarily inherited from V1, but processing that occurs after V1 and possibly within MT computes selective combinations of speed-tuned signals of special relevance for downstream perceptual and motor mechanisms.
我们记录了麻醉、麻痹的猕猴初级视觉皮层（V1）中方向选择性简单细胞和复杂细胞的反应。当用正弦波光栅进行研究时，V1中几乎所有简单细胞的反应在空间和时间频率上都是可分离的：偏好的时间频率不变，偏好速度随光栅的空间频率增加而降低。与先前从中颞视觉区域（MT）的记录一样，大约四分之一的V1复杂细胞对空间和时间频率具有可分离的反应，四分之一在偏好速度不随空间频率变化的意义上是“速度调谐”的。一半处于这两个极端之间。降低光栅的对比度会使V1复杂细胞群体在空间和时间频率调谐上变得更可分离。对比度依赖性可以通过神经元的对比度增益来解释，对于高或低时间和空间频率的光栅，其对比度增益相对较高。对于由两个空间叠加的正弦波光栅组成的刺激，V1神经元的偏好速度和调谐带宽可以根据单独呈现的成分光栅的反应总和来预测，这与MT中显示非线性相互作用的神经元不同。我们得出结论，对比度增益的时空调制通过V1复杂细胞中可分离的输入产生速度调谐。MT中的速度调谐可能主要从V1继承而来，但在V1之后且可能在MT内发生的处理会计算与下游感知和运动机制特别相关的速度调谐信号的选择性组合。
