Department of Neuroscience, Medical University of South Carolina, Charleston, SC 29425.
Department of Physiology, Augusta University, Augusta, GA 30912.
eNeuro. 2020 Mar 23;7(2). doi: 10.1523/ENEURO.0497-19.2020. Print 2020 Mar/Apr.
Two-photon imaging studies in mouse primary visual cortex (V1) consistently report that around half of the neurons respond to oriented grating stimuli. However, in cats and primates, nearly all neurons respond to such stimuli. Here we show that mouse V1 responsiveness and selectivity strongly depends on neuronal depth. Moving from superficial layer 2 down to layer 4, the percentage of visually responsive neurons nearly doubled, ultimately reaching levels similar to what is seen in other species. Over this span, the amplitude of neuronal responses also doubled. Moreover, stimulus selectivity was also modulated, not only with depth but also with response amplitude. Specifically, we found that orientation and direction selectivity were greater in stronger responding neurons, but orientation selectivity decreased with depth whereas direction selectivity increased. Importantly, these depth-dependent trends were found not just between layer 2/3 and layer 4 but at different depths within layer 2/3 itself. Thus, neuronal depth is an important factor to consider when pooling neurons for population analyses. Furthermore, the inability to drive the majority of cells in superficial layer 2/3 of mouse V1 with grating stimuli indicates that there may be fundamental differences in the micro-circuitry and role of V1 between rodents and other mammals.
在小鼠初级视觉皮层（V1）的双光子成像研究中，一致报告说约有一半的神经元对定向光栅刺激有反应。然而，在猫和灵长类动物中，几乎所有的神经元都对这种刺激有反应。在这里，我们表明，小鼠 V1 的反应性和选择性强烈依赖于神经元的深度。从浅层第 2 层移动到第 4 层，对视觉有反应的神经元的比例几乎增加了一倍，最终达到与其他物种相似的水平。在此范围内，神经元反应的幅度也增加了一倍。此外，刺激选择性也受到调节，不仅与深度有关，还与反应幅度有关。具体来说，我们发现，在较强的反应神经元中，方向和方向选择性更大，但方向选择性随深度而降低，而方向选择性随深度而增加。重要的是，这些依赖深度的趋势不仅在第 2/3 层和第 4 层之间存在，而且在第 2/3 层本身的不同深度也存在。因此，在进行群体分析时，神经元的深度是一个需要考虑的重要因素。此外，用光栅刺激不能驱动小鼠 V1 浅层第 2/3 层中的大多数细胞，这表明在啮齿动物和其他哺乳动物之间，V1 的微电路和作用可能存在根本差异。
