Department of Optometry and Vision Sciences, The University of Melbourne Parkville, VIC, Australia.
Front Syst Neurosci. 2011 Oct 11;5:81. doi: 10.3389/fnsys.2011.00081. eCollection 2011.
Controversy remains about how orientation selectivity emerges in simple cells of the mammalian primary visual cortex. In this paper, we present a computational model of how the orientation-biased responses of cells in lateral geniculate nucleus (LGN) can contribute to the orientation selectivity in simple cells in cats. We propose that simple cells are excited by lateral geniculate fields with an orientation-bias and disynaptically inhibited by unoriented lateral geniculate fields (or biased fields pooled across orientations), both at approximately the same retinotopic co-ordinates. This interaction, combined with recurrent cortical excitation and inhibition, helps to create the sharp orientation tuning seen in simple cell responses. Along with describing orientation selectivity, the model also accounts for the spatial frequency and length-response functions in simple cells, in normal conditions as well as under the influence of the GABA(A) antagonist, bicuculline. In addition, the model captures the response properties of LGN and simple cells to simultaneous visual stimulation and electrical stimulation of the LGN. We show that the sharp selectivity for stimulus orientation seen in primary visual cortical cells can be achieved without the excitatory convergence of the LGN input cells with receptive fields along a line in visual space, which has been a core assumption in classical models of visual cortex. We have also simulated how the full range of orientations seen in the cortex can emerge from the activity among broadly tuned channels tuned to a limited number of optimum orientations, just as in the classical case of coding for color in trichromatic primates.
关于哺乳动物初级视皮层简单细胞中取向选择性是如何出现的，仍然存在争议。在本文中，我们提出了一个计算模型，说明外侧膝状体（LGN）细胞的取向偏向反应如何有助于猫的简单细胞中的取向选择性。我们提出，简单细胞被具有取向偏差的外侧膝状体场兴奋，并被无取向的外侧膝状体场（或跨取向汇集的偏置场）双突触抑制，两者在大约相同的视网膜坐标处。这种相互作用，加上皮层的兴奋和抑制的回授，有助于产生简单细胞反应中看到的尖锐取向调谐。除了描述取向选择性之外，该模型还解释了简单细胞的空间频率和长度反应函数，包括正常条件下以及 GABA(A)拮抗剂，印防己毒素的影响下。此外，该模型还捕获了 LGN 和简单细胞对同时视觉刺激和 LGN 电刺激的反应特性。我们表明，初级视皮层细胞中对刺激取向的尖锐选择性可以在没有 LGN 输入细胞与视觉空间中沿一条线的感受野的兴奋汇聚的情况下实现，这一直是经典视皮层模型的核心假设。我们还模拟了如何从对有限数量最佳取向调谐的广泛调谐通道的活动中产生皮层中看到的所有取向，就像三色灵长类动物的颜色编码的经典情况一样。
