Department of Neurosciences, University of California at San Diego, La Jolla, CA 92093, USA.
Proc Natl Acad Sci U S A. 2010 Aug 24;107(34):15246-51. doi: 10.1073/pnas.1006735107. Epub 2010 Aug 9.
Changes in neuronal activity are accompanied by the release of vasoactive mediators that cause microscopic dilation and constriction of the cerebral microvasculature and are manifested in macroscopic blood oxygenation level-dependent (BOLD) functional MRI (fMRI) signals. We used two-photon microscopy to measure the diameters of single arterioles and capillaries at different depths within the rat primary somatosensory cortex. These measurements were compared with cortical depth-resolved fMRI signal changes. Our microscopic results demonstrate a spatial gradient of dilation onset and peak times consistent with "upstream" propagation of vasodilation toward the cortical surface along the diving arterioles and "downstream" propagation into local capillary beds. The observed BOLD response exhibited the fastest onset in deep layers, and the "initial dip" was most pronounced in layer I. The present results indicate that both the onset of the BOLD response and the initial dip depend on cortical depth and can be explained, at least in part, by the spatial gradient of delays in microvascular dilation, the fastest response being in the deep layers and the most delayed response in the capillary bed of layer I.
神经元活动的变化伴随着血管活性介质的释放，这些介质导致脑微血管的微小扩张和收缩，并在宏观血氧水平依赖 (BOLD) 功能磁共振成像 (fMRI) 信号中表现出来。我们使用双光子显微镜测量了大鼠初级体感皮层内不同深度的单个动脉和毛细血管的直径。这些测量结果与皮层深度分辨 fMRI 信号变化进行了比较。我们的微观结果表明，扩张起始和峰值时间存在空间梯度，与沿着潜水动脉向皮层表面的“上游”血管扩张以及向局部毛细血管床的“下游”传播一致。观察到的 BOLD 反应在深层最快开始，而 I 层的“初始下降”最为明显。目前的结果表明，BOLD 反应的起始和初始下降都取决于皮层深度，至少部分可以通过微血管扩张延迟的空间梯度来解释，最快的反应在深层，最延迟的反应在 I 层的毛细血管床。
