van Hateren Hans
Department of Neurobiophysics, University of Groningen, Groningen, The Netherlands.
J Vis. 2005 Apr 15;5(4):331-47. doi: 10.1167/5.4.5.
A model for the sensitivity regulation in the primate outer retina is developed and validated using horizontal cell measurements from the literature. The main conclusion is that the phototransduction of the cones is the key factor regulating sensitivity. The model consists of a nonlinearity cascaded with three feedback control loops. The nonlinearity is caused by the hydrolysis of cGMP by activated phosphodiesterase. The first feedback loop is divisive, with calcium regulating the photocurrent in the cone outer segment. The second feedback loop is also divisive, with voltage-sensitive channels regulating the membrane voltage of the cone inner segment. The final feedback loop is subtractive, where the membrane voltage of the horizontal cell is subtracted from that of the cone before the cone drives the horizontal and bipolar cells. The model describes adequately the major characteristics of the horizontal cell responses to wide field, spectrally white stimuli. In particular, it shows (1) sensitivity and bandwidth control as a function of background intensity; (2) the major nonlinearities observed in the horizontal cells; and (3) the transition from linear responses toward contrast constancy (Weber's law) for background illuminances ranging from 1-1000 td.
利用文献中水平细胞的测量数据，建立并验证了一种灵长类动物外视网膜敏感度调节模型。主要结论是，视锥细胞的光转导是调节敏感度的关键因素。该模型由一个非线性环节和三个反馈控制回路级联组成。非线性是由激活的磷酸二酯酶水解环鸟苷酸（cGMP）引起的。第一个反馈回路是除法型的，钙调节视锥细胞外段的光电流。第二个反馈回路也是除法型的，电压敏感通道调节视锥细胞内段的膜电压。最后一个反馈回路是减法型的，在视锥细胞驱动水平细胞和双极细胞之前，从视锥细胞的膜电压中减去水平细胞的膜电压。该模型充分描述了水平细胞对宽视野、光谱白色刺激的主要反应特征。特别是，它显示出：（1）作为背景强度函数的敏感度和带宽控制；（2）在水平细胞中观察到的主要非线性；以及（3）对于1-1000td范围内的背景照度，从线性反应向对比度恒定（韦伯定律）的转变。
