In the barrel field of the rodent primary somatosensory cortex (S1bf), excitatory cells in layer 2/3 (L2/3) display sparse firing but reliable subthreshold response during whisker stimulation. Subthreshold responses encode specific features of the sensory stimulus, for example, the direction of whisker deflection. According to the canonical model for the flow of sensory information across cortical layers, activity in L2/3 is driven by layer 4 (L4). However, L2/3 cells receive excitatory inputs from other regions, raising the possibility that L4 partially drives L2/3 during whisker stimulation. To test this hypothesis, we combined patch-clamp recordings from L2/3 pyramidal neurons in S1bf with selective optogenetic inhibition of L4 during passive whisker stimulation in both anesthetized and awake head-restrained mice. We found that L4 optogenetic inhibition did not abolish the subthreshold whisker-evoked response nor it affected spontaneous membrane potential fluctuations of L2/3 neurons. However, L4 optogenetic inhibition decreased L2/3 subthreshold responses to whisker deflections in the preferred direction, and it increased L2/3 responses to stimuli in the nonpreferred direction, leading to a change in the direction tuning. Our results contribute to reveal the circuit mechanisms underlying the processing of sensory information in the rodent S1bf.

中文翻译：

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小鼠初级体感皮层第 4 层对第 2/3 层阈下晶须响应的刺激特征特异性控制

在啮齿动物初级体感皮层 (S1bf) 的桶状区域中，第 2/3 层 (L2/3) 中的兴奋性细胞在晶须刺激期间表现出稀疏的放电但可靠的阈下反应。亚阈值反应编码感觉刺激的特定特征，例如，晶须偏转的方向。根据跨皮质层的感觉信息流的规范模型，L2/3 中的活动由第 4 层 (L4) 驱动。然而，L2/3 细胞接收来自其他区域的兴奋性输入，增加了 L4 在晶须刺激期间部分驱动 L2/3 的可能性。为了验证这一假设，我们将 S1bf 中 L2/3 锥体神经元的膜片钳记录与在麻醉和清醒头部约束小鼠的被动胡须刺激过程中对 L4 的选择性光遗传学抑制相结合。我们发现 L4 光遗传学抑制并没有消除阈下晶须诱发的反应，也没有影响 L2/3 神经元的自发膜电位波动。然而，L4 光遗传学抑制降低了 L2/3 阈下对首选方向晶须偏转的反应，并增加了 L2/3 对非首选方向刺激的反应，导致方向调整发生变化。我们的结果有助于揭示啮齿动物 S1bf 感觉信息处理的电路机制。它增加了 L2/3 对非首选方向刺激的反应，导致方向调整的变化。我们的结果有助于揭示啮齿动物 S1bf 感觉信息处理的电路机制。它增加了 L2/3 对非首选方向刺激的反应，导致方向调整的变化。我们的结果有助于揭示啮齿动物 S1bf 感觉信息处理的电路机制。