Ascending sensory information is conveyed from the thalamus to layers 4 and 6 of the sensory cortical areas. Interestingly, receptive field properties of cortical layer-6 neurons differ from those in layer 4. Do such differences reflect distinct inheritance patterns from the thalamus, or are they derived instead from local cortical circuits? To distinguish between these possibilities, we utilized in vitro slice preparations containing the thalamo-cortical pathways of the auditory and somatosensory systems. Responses from neurons in layers 4 and 6 that resided in the same column were recorded using whole-cell patch clamp. Laser-scanning photostimulation via uncaging of glutamate in the thalamus and cortex was used to map the functional topography of thalamo-cortical and intracortical inputs to each layer. In addition, we assessed the functional divergence of thalamo-cortical inputs by optical imaging of flavoprotein autofluorescence. We found that the thalamo-cortical inputs to layers 4 and 6 originated from the same thalamic domain, but the intracortical projections to the same neurons differed dramatically. Our results suggest that the intracortical projections, rather than the thalamic inputs, to each layer contribute more to the differences in their receptive field properties.

中文翻译：

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丘脑和内在投射到皮质层 4 和 6 的功能收敛

上升的感觉信息从丘脑传递到感觉皮层区域的第 4 层和第 6 层。有趣的是，第 6 层皮质神经元的感受野特性与第 4 层不同。这种差异是否反映了来自丘脑的不同遗传模式，或者它们是否源自局部皮质回路？为了区分这些可能性，我们使用了包含听觉和体感系统丘脑皮质通路的体外切片制剂。使用全细胞膜片钳记录位于同一列中的第 4 层和第 6 层神经元的反应。通过在丘脑和皮质中解笼谷氨酸的激光扫描光刺激被用来绘制丘脑皮质和皮质内输入到每一层的功能地形图。此外，我们通过黄素蛋白自发荧光的光学成像评估了丘脑皮质输入的功能差异。我们发现第 4 层和第 6 层的丘脑皮质输入来自相同的丘脑域，但对相同神经元的皮质内投射却截然不同。我们的结果表明，每一层的皮质内投射，而不是丘脑输入，对感受野特性的差异贡献更大。