Victor J D, Blessing E M, Forte J D, Buzás P, Martin P R
Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, NY 10021, USA.
J Physiol. 2007 Feb 15;579(Pt 1):29-51. doi: 10.1113/jphysiol.2006.122283. Epub 2006 Nov 23.
This study concerns the properties of neurons carrying signals for colour vision in primates. We investigated the variability of responses of individual parvocellular lateral geniculate neurons of dichromatic and trichromatic marmosets to drifting sinusoidal luminance and chromatic gratings. Response variability was quantified by the cycle-to-cycle variation in Fourier components of the response. Averaged across the population, the variability at low contrasts was greater than predicted by a Poisson process, and at high contrasts the responses were approximately 40% more variable than responses at low contrasts. The contrast-dependent increase in variability was nevertheless below that expected from the increase in firing rate. Variability falls below the Poisson prediction at high contrast, and intrinsic variability of the spike train decreases as contrast increases. Thus, while deeply modulated responses in parvocellular cells have a larger absolute variability than weakly modulated ones, they have a more favourable signal: noise ratio than predicted by a Poisson process. Similar results were obtained from a small sample of magnocellular and koniocellular ('blue-on') neurons. For parvocellular neurons with pronounced colour opponency, chromatic responses were, on average, less variable (10-15%, p<0.01) than luminance responses of equal magnitude. Conversely, non-opponent parvocellular neurons showed the opposite tendency. This is consistent with a supra-additive noise source prior to combination of cone signals. In summary, though variability of parvocellular neurons is largely independent of the way in which they combine cone signals, the noise characteristics of retinal circuitry may augment specialization of parvocellular neurons to signal luminance or chromatic contrast.
本研究关注灵长类动物中携带颜色视觉信号的神经元的特性。我们研究了二色性和三色性狨猴的单个小细胞外侧膝状神经元对漂移正弦亮度和彩色光栅的反应变异性。通过反应的傅里叶分量的逐周期变化来量化反应变异性。在群体水平上进行平均，低对比度下的变异性大于泊松过程的预测值，而在高对比度下，反应的变异性比低对比度下的反应大约高40%。然而，对比度依赖性的变异性增加低于放电率增加所预期的水平。在高对比度下，变异性低于泊松预测值，并且随着对比度增加，脉冲序列的内在变异性降低。因此，虽然小细胞中的深度调制反应比弱调制反应具有更大的绝对变异性，但它们具有比泊松过程预测的更有利的信噪比。从一小部分大细胞和小细胞（“蓝开”）神经元中也获得了类似的结果。对于具有明显颜色对立性的小细胞神经元，平均而言，颜色反应的变异性比同等幅度的亮度反应小（10 - 15%，p < 0.01）。相反，非对立性小细胞神经元表现出相反的趋势。这与锥体信号组合之前的超加性噪声源一致。总之，虽然小细胞神经元的变异性在很大程度上与它们组合锥体信号的方式无关，但视网膜回路的噪声特性可能会增强小细胞神经元对亮度或颜色对比度信号的特化。
