Sparse coding in striate and extrastriate visual cortex.
Sparse coding in striate and extrastriate visual cortex.
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DOI：
10.1152/jn.00594.2010
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发表时间：
2011-06
影响因子：
2.5
通讯作者：
B. Willmore;J. Mazer;J. Gallant
中科院分区：
文献类型：
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作者：
B. Willmore;J. Mazer;J. Gallant
对哺乳动物皮层的理论研究认为，有效的神经编码应该是稀疏的。然而，理论和实验研究使用了术语“稀疏”的不同定义，导致关于稀疏码的性质的三种假设。首先，具有高寿命稀疏性的代码需要很少的动作电位。其次，终生稀疏代码也是种群稀疏的。第三，对神经编码进行优化，使生命周期稀疏性最大化。在这里，我们详细研究了这些假设，并测试了它们在灵长类动物视觉皮层中的有效性。我们证明了寿命和总体稀疏性并不一定相关，并且无论代码使用多少动作电位，它都可能具有高寿命稀疏性。我们测量了猕猴视觉皮层V1、V2和V4三个区域在呈现自然图像时的寿命稀疏度。我们发现，生命周期稀疏性不会随着视觉层次的增加而增加。这表明神经代码不是简单地优化以最大化生命周期稀疏性。我们还发现，在具有挑战性的视觉任务中，放电率高于基于代谢极限的理论值，V1、V2和V4的反应可以用指数分布很好地描述。这些发现与神经元在平均放电率的代谢限制下被优化以最大化信息传递的假设一致。
Theoretical studies of mammalian cortex argue that efficient neural codes should be sparse. However, theoretical and experimental studies have used different definitions of the term "sparse" leading to three assumptions about the nature of sparse codes. First, codes that have high lifetime sparseness require few action potentials. Second, lifetime-sparse codes are also population-sparse. Third, neural codes are optimized to maximize lifetime sparseness. Here, we examine these assumptions in detail and test their validity in primate visual cortex. We show that lifetime and population sparseness are not necessarily correlated and that a code may have high lifetime sparseness regardless of how many action potentials it uses. We measure lifetime sparseness during presentation of natural images in three areas of macaque visual cortex, V1, V2, and V4. We find that lifetime sparseness does not increase across the visual hierarchy. This suggests that the neural code is not simply optimized to maximize lifetime sparseness. We also find that firing rates during a challenging visual task are higher than theoretical values based on metabolic limits and that responses in V1, V2, and V4 are well-described by exponential distributions. These findings are consistent with the hypothesis that neurons are optimized to maximize information transmission subject to metabolic constraints on mean firing rate.