Direction selectivity of synaptic potentials in simple cells of the cat visual cortex
Direction selectivity of synaptic potentials in simple cells of the cat visual cortex
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DOI：
10.1152/jn.1997.78.5.2772
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发表时间：
1997-11-01
影响因子：
2.5
通讯作者：
Ferster, D
中科院分区：
文献类型：
--
作者：
Jagadeesh, B;Wheat, HS;Ferster, D
视觉皮层中简单细胞的方向选择性至少部分是由非线性机制产生的。如果一个神经元在空间上是线性的，那么它对运动刺激的反应可以通过它对在感受野内不同位置呈现的静止刺激的反应的线性组合来准确地预测。在细胞外记录中，没有发现这种情况。尽管细胞外实验证明了非线性的存在，但非线性背后的细胞过程，无论是早期的突触机制，如分流抑制，还是仅仅是输出端的尖峰阈值，都是未知的。为了区分这些可能性，我们用全细胞贴片技术记录了完整猫的简单细胞的细胞内。用方向选择性线性模型分析了平稳正弦波光栅诱发的突触电位。该模型能相当准确地预测细胞对移动光栅的反应。运动光栅响应的方向选择性和时间过程与模型吻合较好。突触电位的方向选择性明显小于细胞内记录的动作电位，这表明阈值等非线性机制增强了细胞输出的方向选择性，而不是突触输入的方向选择性。然而，在输入阶段，细胞显然以高度线性的方式汇总它们的突触输入。基于主成分分析的更有约束的突触求和线性测试应用于定向选择细胞对固定光栅的响应。分析证实，这些细胞的总和是高度线性的。主成分分析与一个模型是一致的，在这个模型中，皮质简单细胞的方向选择性仅由两个亚基产生，每个亚基具有不同的接受保持位置和响应时间过程。每个两个亚单位的响应时间过程为四个分析的细胞推导。每个衍生的亚基在空间上是线性的，这表明构成每个亚基的神经元要么是膝状x细胞，要么是从x细胞接收初级突触输入。每个亚单元的响应幅度与刺激的对比度呈线性关系。这些子单元在时域上是非线性的，然而，对一个对比度在时间上被正弦调制的平稳刺激的响应是非正弦的。主成分分析不排除基于两个以上亚单元的方向选择性模型，但这种高阶模型必须包括额外的亚单元形成两个亚单元解派生的属性之间的平滑插值连续体的约束。
The direction selectivity of simple cells in the visual cortex is generated at least in part by nonlinear mechanisms. If a neuron were spatially linear, its responses to moving stimuli could be predicted accurately from linear combinations of its responses to stationary stimuli presented at different positions within the receptive field. In extracellular recordings, this has not been found to be the case. Although the extracellular experiments demonstrate the presence of a nonlinearity, the cellular process underlying the nonlinearity, whether an early synaptic mechanism such as a shunting inhibition or simply the spike threshold at the output is not known. To differentiate between these possibilities, we have recorded intracellularly from simple cells of the intact cat with the whole cell patch technique. A linear model of direction selectivity was used to analyze the synaptic potentials evoked by stationary sine-wave gratings. The model predicted the responses of cells to moving gratings with considerable accuracy. The degree of direction selectivity and the time course of the responses to moving gratings were both well matched by the model. The direction selectivity of the synaptic potentials was considerably smaller than that of the intracellularly recorded action potential, indicating that a nonlinear mechanism such as threshold enhances the direction selectivity of the cell's output over that of its synaptic inputs. At the input stage, however, the cells apparently sum their synaptic inputs in a highly linear fashion. A more constrained test of linearity of synaptic summation based on principal component analysis was applied to the responses of direction-selective cells to stationary gratings. The analysis confirms that the summation in these cells is highly linear. The principal component analysis is consistent with a model in which direction selectivity in cortical simple cells is generated by only two subunits, each with a different receptive-held position and response time course. The response time course for each of the two subunits is derived for four analyzed cells. Each derived subunit is linear in spatial summation, suggesting that the neurons that comprise each subunit are either geniculate X-cells or receive their primary synaptic input from X-cells. The amplitude of the response of each subunit is linearly related to the contrast of the stimulus. The subunits are nonlinear in the time domain, however: the response to a stationary stimulus whose contrast is modulated sinusoidally in time is nonsinusoidal. The principal component analysis does not exclude models of direction selectivity based on more than two subunits, but such higher-order models would have to include the constraint that the extra subunits form a smooth continuum of interpolation between the properties derived from the two subunit solution.