Netherlands Institute for Neuroscience, Meibergdreef 47, 1105 BA Amsterdam, The Netherlands.
J Physiol. 2010 Feb 1;588(Pt 3):435-46. doi: 10.1113/jphysiol.2009.179036. Epub 2009 Dec 14.
Visual information in natural scenes is distributed over a broad range of intensities and contrasts. This distribution has to be compressed in the retina to match the dynamic range of retinal neurons. In this study we examined how cones perform this compression and investigated which physiological processes contribute to this operation. M- and L-cones of the goldfish were stimulated with a natural time series of intensities (NTSI) and their responses were recorded. The NTSI displays an intensity distribution which is skewed towards the lower intensities and has a long tail into the high intensity region. Cones transform this skewed distribution into a more symmetrical one. The voltage responses of the goldfish cones were compared to those of a linear filter and a non-linear biophysical model of the photoreceptor. The results show that the linear filter under-represents contrasts at low intensities compared to the actual cone whereas the non-linear biophysical model performs well over the whole intensity range used. Quantitative analysis of the two approaches indicates that the non-linear biophysical model can capture 91 +/- 5% of the coherence rate (a biased measure of information rate) of the actual cone, where the linear filter only reaches 48 +/- 8%. These results demonstrate that cone photoreceptors transform an NTSI in a non-linear fashion. The comparison between current clamp and voltage clamp recordings and analysis of the behaviour of the biophysical model indicates that both the calcium feedback loop in the outer segment and the hydrolysis of cGMP are the major components that introduce the specific non-linear response properties found in the goldfish cones.
自然场景中的视觉信息分布在很宽的强度和对比度范围内。这种分布必须在视网膜中压缩，以匹配视网膜神经元的动态范围。在这项研究中，我们研究了视锥细胞如何进行这种压缩，并探讨了哪些生理过程有助于这种操作。我们用自然强度时间序列（NTSI）刺激金鱼的 M-和 L-视锥细胞，并记录它们的反应。NTSI 显示出一种向低强度倾斜且高强度区域长尾的强度分布。视锥细胞将这种倾斜分布转换为更对称的分布。我们将金鱼视锥细胞的电压反应与线性滤波器和光感受器的非线性生物物理模型进行了比较。结果表明，与实际视锥细胞相比，线性滤波器在低强度对比度下的表示不足，而非线性生物物理模型在使用的整个强度范围内表现良好。对这两种方法的定量分析表明，非线性生物物理模型可以捕获实际视锥的 91 +/- 5%的相干率（信息率的一种有偏度量），而线性滤波器仅达到 48 +/- 8%。这些结果表明，视锥细胞以非线性方式转换 NTSI。电流箝位和电压箝位记录的比较以及生物物理模型行为的分析表明，外段中的钙反馈环和 cGMP 的水解都是在金鱼视锥细胞中产生特定非线性响应特性的主要成分。
