Molnar Alyosha, Hsueh Hain-Ann, Roska Botond, Werblin Frank S
School of Electrical and Computer Engineering (ECE), Cornell University, Ithaca, NY 14853, USA.
J Comput Neurosci. 2009 Dec;27(3):569-90. doi: 10.1007/s10827-009-0170-6. Epub 2009 Jul 28.
In the mammalian retina, complementary ON and OFF visual streams are formed at the bipolar cell dendrites, then carried to amacrine and ganglion cells via nonlinear excitatory synapses from bipolar cells. Bipolar, amacrine and ganglion cells also receive a nonlinear inhibitory input from amacrine cells. The most common form of such inhibition crosses over from the opposite visual stream: Amacrine cells carry ON inhibition to the OFF cells and carry OFF inhibition to the ON cells ("crossover inhibition"). Although these synapses are predominantly nonlinear, linear signal processing is required for computing many properties of the visual world such as average intensity across a receptive field. Linear signaling is also necessary for maintaining the distinction between brightness and contrast. It has long been known that a subset of retinal outputs provide exactly this sort of linear representation of the world; we show here that rectifying (nonlinear) synaptic currents, when combined thorough crossover inhibition can generate this linear signaling. Using simple mathematical models we show that for a large set of cases, repeated rounds of synaptic rectification without crossover inhibition can destroy information carried by those synapses. A similar circuit motif is employed in the electronics industry to compensate for transistor nonlinearities in analog circuits.
在哺乳动物视网膜中，互补的ON和OFF视觉信息流在双极细胞树突处形成，然后通过双极细胞的非线性兴奋性突触传递至无长突细胞和神经节细胞。双极细胞、无长突细胞和神经节细胞还从无长突细胞接收非线性抑制性输入。这种抑制最常见的形式是从相反的视觉信息流交叉过来：无长突细胞将ON抑制传递给OFF细胞，并将OFF抑制传递给ON细胞（“交叉抑制”）。尽管这些突触主要是非线性的，但计算视觉世界的许多属性（如感受野内的平均强度）需要线性信号处理。线性信号对于维持亮度和对比度之间的区别也很必要。长期以来人们就知道，视网膜输出的一个子集提供了这种对世界的线性表示；我们在此表明，整流（非线性）突触电流与交叉抑制相结合时可以产生这种线性信号。使用简单的数学模型，我们表明在大量情况下，没有交叉抑制的重复突触整流轮次会破坏这些突触携带的信息。电子工业中采用了类似的电路模式来补偿模拟电路中的晶体管非线性。
