Orientation tuning of input conductance, excitation, and inhibition in cat primary visual cortex
Orientation tuning of input conductance, excitation, and inhibition in cat primary visual cortex
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DOI：
10.1152/jn.2000.84.2.909
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发表时间：
2000-08-01
影响因子：
2.5
通讯作者：
Ferster, D
中科院分区：
文献类型：
--
作者：
Anderson, JS;Carandini, M;Ferster, D
最近研究表明，猫初级视觉皮质(V1)细胞的输入电导在视觉刺激过程中显著增加。由于增加电导可能会对突触输入产生分裂效应，理论建议将其归因于特定的功能。根据否决权模型，电导的增加将有助于通过在非最佳取向时增加最多来加强取向调整。根据归一化模型，电导的增加将通过与刺激方向无关和通过刺激对比度生长来控制细胞的增益。我们开始测试这些提议，并确定电导增加的视觉特性和可能的突触来源。我们在注入稳定电流的同时记录了CAT V1细胞的膜电位，并呈现出不同对比度和方向的漂移光栅图。在刺激对比度为20%-300%的情况下，输入电导增加了20%-300%，一般情况下，简单细胞(40%-300%)比复杂细胞(20%-120%)的输入电导增加得更多，而且简单细胞在时间上受到强烈的调制。对于优先取向的刺激，电导总是最大的。因此，电导变化有助于增益控制机制，但该增益控制的强度并不唯一地依赖于对比度。通过假设电导的变化完全是突触的，我们进一步推导出了视觉反应背后的兴奋性和抑制性突触电导。在简单细胞中，这些电导通常以推-拉方式排列：当抑制减少时，兴奋增加，反之亦然。兴奋和抑制具有相似的优先取向，在调谐宽度上似乎没有不同，这表明猫V1简单细胞的皮质内突触输入来自具有相似定向调谐的细胞。这一发现与简单细胞中的取向调整是通过非最佳取向的抑制实现的模型不同，或者是通过比激发更广泛地调整的抑制来实现的。
The input conductance of cells in the cat primary visual cortex (V1) has been shown recently to grow substantially during visual stimulation. Because increasing conductance can have a divisive effect on the synaptic input, theoretical proposals have ascribed to it specific functions. According to the veto model, conductance increases would serve to sharpen orientation tuning by increasing most at off-optimal orientations. According to the normalization model, conductance increases would control the cell's gain, by being independent of stimulus orientation and by growing with stimulus contrast. We set out to test these proposals and to determine the visual properties and possible synaptic origin of the conductance increases. We recorded the membrane potential of cat V1 cells while injecting steady currents and presenting drifting grating patterns of varying contrast and orientation. Input conductance grew with stimulus contrast by 20-300%, generally more in simple cells (40-300%) than in complex cells (20-120%), and in simple cells was strongly modulated in time. Conductance was invariably maximal for stimuli of the preferred orientation. Thus conductance changes contribute to a gain control mechanism, but the strength of this gain control does not depend uniquely on contrast. By assuming that the conductance changes are entirely synaptic, we further derived the excitatory and inhibitory synaptic conductances underlying the visual responses. In simple cells, these conductances were often arranged in push-pull: excitation increased when inhibition decreased and vice versa. Excitation and inhibition had similar preferred orientations and did not appear to differ in tuning width, suggesting that the intracortical synaptic inputs to simple cells of cat V1 originate from cells with similar orientation tuning. This finding is at odds with models where orientation tuning in simple cells is achieved by inhibition at off-optimal orientations or sharpened by inhibition that is more broadly tuned than excitation.