易经里强调三易，首当其冲的就是“简易”（其他为“变异”，“不易”）。其实神经科学里关于视觉的研究，也有相似的概念。不过这里叫sparseness，即稀疏。花花世界，不需要借我们一双慧眼，就可用很少的视觉神经元进行编码，从而看清了。

    尽管许多视觉系统的研究都停留在经典感受野 (classical receptive field, CRF)，但不可否认，正是经典感受野和非经典感受野的联合作用，即CRF+nCRF，使得神经响应变得稀疏的。但其中的细胞层面和网络层面的机理，至今还是个迷。最近一篇发表在《neuron》上的文章，向前迈进了一步。他们用猫做实验，用自然图景刺激他们的初级视觉皮层。结果发现，CRF+nCRF可以提高初级视觉皮层椎体细胞响应的稀疏性，可靠性和准确性。稀疏性的提高伴随着抑制阀的提高和突触电位的缩小。他们还建立了一个简单的计算模型来重复这一现象。对视觉建模感兴趣的网友可以关注一下。

 

Neuron, Volume 65, Issue 1, 107-121, 14 January 2010

Synaptic and Network Mechanisms of Sparse and Reliable Visual Cortical Activity during Nonclassical Receptive Field Stimulation

Haider et al.

During natural vision, the entire visual field is stimulated by images rich in spatiotemporal structure. Although many visual system studies restrict stimuli to the classical receptive field (CRF), it is known that costimulation of the CRF and the surrounding nonclassical receptive field (nCRF) increases neuronal response sparseness. The cellular and network mechanisms underlying increased response sparseness remain largely unexplored. Here we show that combined CRF + nCRF stimulation increases the sparseness, reliability, and precision of spiking and membrane potential responses in classical regular spiking (RSC) pyramidal neurons of cat primary visual cortex. Conversely, fast-spiking interneurons exhibit increased activity and decreased selectivity during CRF + nCRF stimulation. The increased sparseness and reliability of RSC neuron spiking is associated with increased inhibitory barrages and narrower visually evoked synaptic potentials. Our experimental observations were replicated with a simple computational model, suggesting that network interactions among neuronal subtypes ultimately sharpen recurrent excitation, producing specific and reliable visual responses.

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