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arXiv 1201.3552q-bio.NC
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视网膜对高阶刺激统计量变化的适应性和不变性

Retinal adaptation and invariance to changes in higher-order stimulus statistics

Gašper Tkačik, Anandamohan Ghosh, Elad Schneidman, Ronen Segev

摘要:

视网膜中的适应被认为是将自然光信号编码为发送到大脑的尖峰序列的优化。然而,自适应也需要计算成本:自适应代码本质上是模糊的,因为输出符号不能简单地映射回刺激,而不知道编码神经元的自适应状态。因此,重要的是要了解输入中的哪些统计变化会引起适应性反应,哪些不会引起适应性反应,并询问适应性潜在限制的原因。我们测量了虎蝾螈视网膜神经节细胞的反应,以控制变化的第二(对比度),第三(偏斜)和第四(峰度)时刻的光强度分布的空间均匀的时间独立的刺激。刺激的偏斜度和峰度被选择为覆盖在自然场景中观察到的范围。我们通过研究二维线性-非线性模型来量化神经节细胞的适应性,该模型能够很好地捕捉所有刺激的视网膜编码特性。我们发现,视网膜神经节细胞适应对比度,但表现出显着的高阶统计量的变化不变的行为。最后,通过理论分析LN型模型中的最优编码,我们证明了神经编码可以保持高的信息速率,而无需动态适应,尽管刺激偏斜和峰度发生变化。

英文摘要:

Adaptation in the retina is thought to optimize the encoding of natural light signals into sequences of spikes sent to the brain. However, adaptation also entails computational costs: adaptive code is intrinsically ambiguous, because output symbols cannot be trivially mapped back to the stimuli without the knowledge of the adaptive state of the encoding neuron. It is thus important to learn which statistical changes in the input do, and which do not, invoke adaptive responses, and ask about the reasons for potential limits to adaptation. We measured the ganglion cell responses in the tiger salamander retina to controlled changes in the second (contrast), third (skew) and fourth (kurtosis) moments of the light intensity distribution of spatially uniform temporally independent stimuli. The skew and kurtosis of the stimuli were chosen to cover the range observed in natural scenes. We quantified adaptation in ganglion cells by studying two-dimensional linear-nonlinear models that capture well the retinal encoding properties across all stimuli. We found that the retinal ganglion cells adapt to contrast, but exhibit remarkably invariant behavior to changes in higher-order statistics. Finally, by theoretically analyzing optimal coding in LN-type models, we showed that the neural code can maintain a high information rate without dynamic adaptation despite changes in stimulus skew and kurtosis.

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