Gur Moshe, Snodderly D Max
Department of Biomedical Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel.
J Physiol. 2008 May 1;586(9):2293-306. doi: 10.1113/jphysiol.2008.151795. Epub 2008 Mar 6.
The physiological literature does not distinguish between the superficial layers 2 and 3 of the primary visual cortex even though these two layers differ in their cytoarchitecture and anatomical connections. To distinguish layer 2 from layer 3, we have analysed the response characteristics of neurons recorded during microelectrode penetrations perpendicular to the cortical surface. Extracellular responses of single neurons to sweeping bars were recorded while macaque monkeys performed a fixation task. Data were analysed from penetrations where cells could be localized to specific depths in the cortex. Although the most superficial cells (depth, 145-371 microm; presumably layer 2) responded preferentially to particular stimulus orientations, they were less selective than cells encountered immediately beneath them (depth, 386-696 microm; presumably layer 3). Layer 2 cells had smaller spikes, higher levels of ongoing activity, larger receptive field activating regions, and less finely tuned selectivity for stimulus orientation and length than layer 3 cells. Direction selectivity was found only in layer 3. These data suggest that layer 3 is involved in generating and transmitting precise, localized information about image features, while the lesser selectivity of layer 2 cells may participate in top-down influences from higher cortical areas, as well as modulatory influences from subcortical brain regions.
生理学文献并未区分初级视觉皮层的表层2和表层3，尽管这两层在细胞结构和解剖学连接上存在差异。为了区分第2层和第3层，我们分析了在垂直于皮质表面的微电极穿刺过程中记录的神经元的反应特性。在猕猴执行固定任务时，记录单个神经元对横扫光条的细胞外反应。分析的数据来自那些细胞能够定位到皮质特定深度的穿刺记录。尽管最表层的细胞（深度为145 - 371微米；推测为第2层）对特定的刺激方向有优先反应，但它们的选择性不如其下方紧邻的细胞（深度为386 - 696微米；推测为第3层）。与第3层细胞相比，第2层细胞的锋电位较小，持续活动水平较高，感受野激活区域较大，对刺激方向和长度的选择性调整较不精细。方向选择性仅在第3层中发现。这些数据表明，第3层参与生成和传递有关图像特征的确切、局部信息，而第2层细胞较低的选择性可能参与来自更高皮质区域的自上而下的影响，以及来自皮质下脑区的调节性影响。
