The stabilized supralinear network accounts for the contrast dependence of visual cortical gamma oscillations
The stabilized supralinear network accounts for the contrast dependence of visual cortical gamma oscillations
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DOI：
10.1101/2023.05.11.540442
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发表时间：
2023-05
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通讯作者：
Caleb J. Holt;K. Miller;Yashar Ahmadian
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作者：
Caleb J. Holt;K. Miller;Yashar Ahmadian
当受到刺激时，视皮层中的神经群会表现出快速的节律性活动，频率在伽马频段(30-80赫兹)。伽马节律在记录的局部场势的功率谱中表现为一个宽共振峰，表现出各种刺激依赖性。特别是在猕猴初级视皮层(V1)，伽马峰值频率随着刺激对比度的增加而增加。此外，这种对比度依赖是局部的：当对比度在视觉空间内平稳变化时，每个皮质柱中的伽马峰值频率由该柱接受野中的局部对比度控制。对于V1伽马振荡的这些对比度相关性，还没有提出简明的机制解释。稳定的超线性网络(SSN)是一种大脑皮层环路的机制模型，它解释了一系列视觉皮质反应的非线性和上下文调制，以及它们的对比度相关性。在这里，我们首先证明了一个简化的SSN模型在没有视网膜复制的情况下稳健地捕捉到了伽马峰值频率的对比度依赖关系，并基于观察到的V1神经元的非饱和和超线性输入输出函数为这种影响提供了机制解释。根据这一结果，局部对对比的依赖可以在视网膜定位的SSN中很容易地捕捉到，但它的皮质柱之间缺乏水平突触连接。然而，V1中的长距离水平连接实际上是强大的，并构成了诸如环绕抑制等语境调制效应的基础。因此，我们探索了具有强兴奋性水平连接的V1的视网膜组织SSN模型是否可以既表现出环绕抑制又表现出伽马峰值频率的局部对比度依赖。我们发现，视网膜定位SSN可以解释这两种影响，但只有当水平兴奋投影由两个随距离具有不同空间衰减模式的分量组成时才能解释这两种影响：仅以源列为目标的短程分量，以及以源列附近的列为目标的远程分量。因此，我们对猕猴V1的水平连接空间结构做出了特定的定性预测，与大脑皮质的柱状结构相一致。
When stimulated, neural populations in the visual cortex exhibit fast rhythmic activity with frequencies in the gamma band (30-80 Hz). The gamma rhythm manifests as a broad resonance peak in the powerspectrum of recorded local field potentials, which exhibits various stimulus dependencies. In particular, in macaque primary visual cortex (V1), the gamma peak frequency increases with increasing stimulus contrast. Moreover, this contrast dependence is local: when contrast varies smoothly over visual space, the gamma peak frequency in each cortical column is controlled by the local contrast in that column’s receptive field. No parsimonious mechanistic explanation for these contrast dependencies of V1 gamma oscillations has been proposed. The stabilized supralinear network (SSN) is a mechanistic model of cortical circuits that has accounted for a range of visual cortical response nonlinearities and contextual modulations, as well as their contrast dependence. Here, we begin by showing that a reduced SSN model without retinotopy robustly captures the contrast dependence of gamma peak frequency, and provides a mechanistic explanation for this effect based on the observed non-saturating and supralinear input-output function of V1 neurons. Given this result, the local dependence on contrast can trivially be captured in a retinotopic SSN which however lacks horizontal synaptic connections between its cortical columns. However, long-range horizontal connections in V1 are in fact strong, and underlie contextual modulation effects such as surround suppression. We thus explored whether a retinotopically organized SSN model of V1 with strong excitatory horizontal connections can exhibit both surround suppression and the local contrast dependence of gamma peak frequency. We found that retinotopic SSNs can account for both effects, but only when the horizontal excitatory projections are composed of two components with different patterns of spatial fall-off with distance: a short-range component that only targets the source column, combined with a long-range component that targets columns neighboring the source column. We thus make a specific qualitative prediction for the spatial structure of horizontal connections in macaque V1, consistent with the columnar structure of cortex.