Department of Psychology, University of Sheffield, Sheffield S10 2TN, United Kingdom.
J Neurosci. 2010 Mar 24;30(12):4285-94. doi: 10.1523/JNEUROSCI.6063-09.2010.
Modern neuroimaging techniques rely on neurovascular coupling to show regions of increased brain activation. However, little is known of the neurovascular coupling relationships that exist for inhibitory signals. To address this issue directly we developed a preparation to investigate the signal sources of one of these proposed inhibitory neurovascular signals, the negative blood oxygen level-dependent (BOLD) response (NBR), in rat somatosensory cortex. We found a reliable NBR measured in rat somatosensory cortex in response to unilateral electrical whisker stimulation, which was located in deeper cortical layers relative to the positive BOLD response. Separate optical measurements (two-dimensional optical imaging spectroscopy and laser Doppler flowmetry) revealed that the NBR was a result of decreased blood volume and flow and increased levels of deoxyhemoglobin. Neural activity in the NBR region, measured by multichannel electrodes, varied considerably as a function of cortical depth. There was a decrease in neuronal activity in deep cortical laminae. After cessation of whisker stimulation there was a large increase in neural activity above baseline. Both the decrease in neuronal activity and increase above baseline after stimulation cessation correlated well with the simultaneous measurement of blood flow suggesting that the NBR is related to decreases in neural activity in deep cortical layers. Interestingly, the magnitude of the neural decrease was largest in regions showing stimulus-evoked positive BOLD responses. Since a similar type of neural suppression in surround regions was associated with a negative BOLD signal, the increased levels of suppression in positive BOLD regions could importantly moderate the size of the observed BOLD response.
现代神经影像学技术依赖于神经血管耦合来显示大脑激活区域的增加。然而，对于抑制性信号存在的神经血管耦合关系知之甚少。为了直接解决这个问题，我们开发了一种制备方法来研究这些提议的抑制性神经血管信号之一的信号源，即大鼠体感皮层中的负血氧水平依赖性（BOLD）反应（NBR）。我们发现了一种在大鼠体感皮层中响应单侧电胡须刺激的可靠的 NBR，它位于正 BOLD 反应相对较深的皮层层中。单独的光学测量（二维光学成像光谱和激光多普勒流量测量）表明，NBR 是由于血液体积和流量减少以及脱氧血红蛋白水平增加所致。通过多通道电极测量的 NBR 区域的神经活动随皮层深度而变化很大。深层皮层层中的神经元活动减少。在停止胡须刺激后，基线以上的神经活动会大幅增加。神经元活动的减少和刺激停止后的基线以上增加都与血流的同时测量密切相关，这表明 NBR 与深层皮层层中神经元活动的减少有关。有趣的是，在显示刺激诱发正 BOLD 反应的区域中，神经减少的幅度最大。由于周围区域中类似的神经抑制与负 BOLD 信号相关，因此正 BOLD 区域中抑制水平的增加可能重要地调节了观察到的 BOLD 反应的大小。
