Contrast invariance of functional maps in cat primary visual cortex
Contrast invariance of functional maps in cat primary visual cortex
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DOI：
10.1167/4.3.1
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发表时间：
2004-01-01
影响因子：
1.8
通讯作者：
Sengpiel, F
中科院分区：
文献类型：
--
作者：
Carandini, M;Sengpiel, F
猫初级视皮层（V1）的神经元根据它们对刺激位置、方向、空间频率和呈现眼的偏好而聚类，从而产生功能图。然而，对于刺激对比度，是否存在类似的布置尚不清楚。在猫V1的神经元在其对比度的反应有很大的不同，并可能在这方面的系统的方式聚集。此外，刺激对比度可能会影响其他功能图。例如，关于细胞色素氧化酶斑点中神经元的对比度阈值是否低于其他地方，一直存在争议。在这里，我们对内在信号进行了成像，以在一系列对比度水平下测量猫V1的方向图。我们确定，逐像素的基础上，对比度响应函数和方向调整曲线。描述对比度反应的拟合参数或多或少是一致的：我们没有发现神经元的对比度阈值比其他地方低的区域。如果这样的区域确实存在，那么它们的功能地图一定比定向偏好地图弱得多。此外，我们发现，对比度没有影响地图的方向偏好：每个像素的方向选择性是不变的刺激对比度。我们在映射水平上证明的对比度不变性在单个神经元水平上是众所周知的。这表明，对像素响应有贡献的神经元通常具有相似的方向偏好或相似的对比度响应。后一种解释可能适用于风车中心，在那里附近神经元的优先方向可以明显不同。总之，我们的数据表明，在猫V1的表面上，对比度是均匀的，对比度的变化不会影响方向偏好的地图。
Neurons in cat primary visual cortex (V1) are clustered according to their preference for stimulus position, orientation, spatial frequency, and eye of presentation, thereby giving rise to functional maps. It is not known, however, whether a similar arrangement is present for stimulus contrast. Neurons in cat V1 vary considerably in their contrast responses, and might be clustered in a systematic fashion in this respect. Additionally, stimulus contrast might affect other functional maps. For example, there has been debate over whether the contrast threshold of neurons in cytochrome oxidase blobs is lower than elsewhere. Here we have imaged intrinsic signals to measure orientation maps in cat V1 at a range of contrast levels. We determined, on a pixel-by-pixel basis, contrast-response functions and orientation tuning curves. The fit parameters describing contrast responses were more or less uniform: We found no regions where neurons have lower contrast threshold than elsewhere. If such regions do exist, their functional maps must be substantially weaker than maps of orientation preference. Moreover, we found that contrast has no impact on maps of orientation preference: The orientation selectivity of each pixel is invariant with stimulus contrast. The contrast invariance that we demonstrate at the level of maps is well known at the level of single neurons. It suggests that neurons contributing to a pixel response generally have similar orientation preferences or similar contrast responses. The latter explanation is likely to hold in pinwheel centers, where preferred orientation of nearby neurons can differ markedly. In summary, our data suggest that contrast is represented uniformly over the surface of cat V1, and changes in contrast do not affect maps of orientation preference.