Jasdzewski G, Strangman G, Wagner J, Kwong K K, Poldrack R A, Boas D A
Athinoula M. Martinos Center, Massachusetts General Hospital, Harvard Medical School, 149 13th St., Charlestown, MA 02129, USA.
Neuroimage. 2003 Sep;20(1):479-88. doi: 10.1016/s1053-8119(03)00311-2.
Several current brain imaging techniques rest on the assumption of a tight coupling between neural activity and hemodynamic response. The nature of this neurovascular coupling, however, is not completely understood. There is some evidence for a decoupling of these processes at the onset of neural activity, which manifests itself as a momentary increase in the relative concentration of deoxyhemoglobin (HbR). The existence of this early component of the hemodynamic response function, however, is controversial, as it is inconsistently found. Near infrared spectroscopy (NIRS) allows quantification of levels of oxyhemoglobin (HbO(2)) and HbR during task performance in humans. We acquired NIRS data during performance of simple motor and visual tasks, using rapid-presentation event-related paradigms. Our results demonstrate that rapid, event-related NIRS can provide robust estimates of the hemodynamic response without artifacts due to low-frequency signal components, unlike data from blocked designs. In both the motor and visual data the onset of the increase in HbO(2) occurs before HbR decreases, and there is a poststimulus undershoot. Our results also show that total blood volume (HbT) drops before HbO(2) and undershoots baseline, raising a new issue for neurovascular models. We did not find early deoxygenation in the motor data using physiologically plausible values for the differential pathlength factor, but did find one in the visual data. We suggest that this difference, which is consistent with functional magnetic resonance imaging (fMRI) data, may be attributable to different capillary transit times in these cortices.
目前的几种脑成像技术基于神经活动与血液动力学反应紧密耦合的假设。然而，这种神经血管耦合的本质尚未完全理解。有一些证据表明，在神经活动开始时这些过程会解耦，表现为脱氧血红蛋白（HbR）相对浓度的瞬间增加。然而，血液动力学反应函数这一早期成分的存在存在争议，因为其发现并不一致。近红外光谱（NIRS）能够在人类执行任务期间对氧合血红蛋白（HbO₂）和HbR的水平进行量化。我们使用快速呈现的事件相关范式，在执行简单运动和视觉任务期间获取了NIRS数据。我们的结果表明，与来自组块设计的数据不同，快速的、事件相关的NIRS能够提供血液动力学反应的可靠估计，而不会受到低频信号成分的干扰。在运动和视觉数据中，HbO₂增加的起始都发生在HbR降低之前，并且刺激后存在下冲。我们的结果还表明，总血容量（HbT）在HbO₂之前下降并低于基线，这为神经血管模型提出了一个新问题。在使用生理上合理的差分程长因子值时，我们在运动数据中未发现早期脱氧现象，但在视觉数据中发现了。我们认为，这种与功能磁共振成像（fMRI）数据一致的差异，可能归因于这些皮层中不同的毛细血管传输时间。
