Adaptive and Regenerative Software Systems, Department of Computer Science and Electrical Engineering, University of Rostock, Albert-Einstein-Str. 21, 18059 Rostock, Germany.
Neuroimage. 2010 Sep;52(3):777-92. doi: 10.1016/j.neuroimage.2010.01.032. Epub 2010 Jan 15.
Neuronal responses in primary visual cortex (V1) to optimally oriented high-contrast stimuli in the receptive field (RF) center are suppressed by stimuli in the RF surround, but can be facilitated when the RF center is stimulated at low contrast. The neural circuits and mechanisms for surround modulation are still unknown. We previously proposed that topdown feedback connections mediate suppression from the "far" surround, while "near' surround suppression is mediated primarily by horizontal connections. We implemented this idea in a recurrent network model of V1. A model assumption needed to account for the contrast-dependent sign of surround modulation is a response asymmetry between excitation and inhibition; accordingly, inhibition, but not excitation, is silent for weak visual inputs to the RF center, and surround stimulation can evoke facilitation. A prediction stemming from this same assumption is that surround suppression is weaker for low than for high contrast stimuli in the RF center. Previous studies are inconsistent with this prediction. Using single unit recordings in macaque V1, we confirm this model's prediction. Model simulations demonstrate that our results can be reconciled with those from previous studies. We also performed a systematic comparison of the experimentally measured surround suppression strength with predictions of the model operated in different parameter regimes. We find that the original model, with strong horizontal and no feedback excitation of local inhibitory neurons, can only partially account quantitatively for the experimentally measured suppression. Strong direct feedback excitation of V1 inhibitory neurons is necessary to account for the experimentally measured surround suppression strength.
初级视皮层 (V1) 中对感受野 (RF) 中心最佳定向高对比度刺激的神经元反应受到 RF 周围刺激的抑制，但当 RF 中心以低对比度刺激时，反应可以被促进。RF 周围调制的神经回路和机制尚不清楚。我们之前提出，自上而下的反馈连接介导来自“远”周围的抑制，而“近”周围抑制主要由水平连接介导。我们在 V1 的递归网络模型中实现了这一想法。为了说明 RF 中心周围调制的对比度依赖性符号，需要一个模型假设，即兴奋和抑制之间存在反应不对称；因此，对于 RF 中心的弱视觉输入，抑制而不是兴奋是沉默的，并且周围刺激可以引发促进。同样的假设还预测，与高对比度刺激相比，低对比度刺激的 RF 中心周围抑制较弱。先前的研究与这一预测不一致。使用猕猴 V1 中的单个单元记录，我们证实了该模型的预测。模型模拟表明，我们的结果可以与以前研究的结果相协调。我们还对实验测量的周围抑制强度与模型在不同参数范围内的预测进行了系统比较。我们发现，具有强水平和无局部抑制神经元直接反馈兴奋的原始模型，只能部分定量解释实验测量的抑制。必须有强烈的 V1 抑制神经元的直接反馈兴奋来解释实验测量的周围抑制强度。
