The contribution of noise to contrast invariance of orientation tuning in cat visual cortex
The contribution of noise to contrast invariance of orientation tuning in cat visual cortex
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DOI：
10.1126/science.290.5498.1968
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发表时间：
2000-12-08
期刊：
影响因子：
56.9
通讯作者：
Ferster, D
中科院分区：
文献类型：
--
作者：
Anderson, JS;Lampl, I;Ferster, D
视觉皮层的前馈模型似乎与皮层细胞的一个众所周知的特性不一致：方向调谐的对比度不变性。模型的固定阈值随着对比度的增加而加宽取向调谐，而在真实的细胞中，调谐宽度不随对比度而变化。我们比较了单细胞锋电位和膜电位响应的方向调谐。两者都是对比度不变的，但应用于膜电位的阈值线性关系准确地预测了尖峰响应的取向调谐。这个明显矛盾的关键在于膜电位的噪声。平均低于阈值的反应仍然能够在单个试验中产生尖峰。与冰山效应不同，即使阈值缩小了方向选择性，对比度不变性也保持不变。噪声可以通过扩展来平滑整个大脑中膜电位和尖峰频率之间的平均关系。
Feedforward models of visual cortex appear to be inconsistent with a well-known property of cortical cells: contrast invariance of orientation tuning. The models' fixed threshold broadens orientation tuning as contrast increases, whereas in real cells tuning width is invariant with contrast. We have compared the orientation tuning of spike and membrane potential responses in single cells. Both are contrast invariant, yet a threshold-linear relation applied to the membrane potential accurately predicts the orientation tuning of spike responses. The key to this apparent paradox lies in the noisiness of the membrane potential. Responses that are subthreshold on average are still capable of generating spikes on individual trials. Unlike the iceberg effect, contrast invariance remains intact even as threshold narrows orientation selectivity. Noise may, by extension, smooth the average relation between membrane potential and spike rate throughout the brain.