Origin of negative blood oxygenation level-dependent fMRI signals
Origin of negative blood oxygenation level-dependent fMRI signals
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DOI：
10.1097/00004647-200208000-00002
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发表时间：
2002-08-01
影响因子：
6.3
通讯作者：
Kim, SG
中科院分区：
文献类型：
--
作者：
Harel, N;Lee, SP;Kim, SG
功能磁共振成像 (fMRI) 技术基于这样的假设：尖峰活动的变化伴随着血氧水平依赖性 (BOLD) 信号的调制。除了常规增加的 BOLD 信号外。偶尔会观察到持续的负 BOLD 信号变化，并被认为反映了神经活动的减少。在本研究中，使用 T-2* 加权 BOLD 和脑血容量 (CBV) 技术对异氟烷麻醉的猫研究了负 BOLD 信号的来源。在视觉刺激期间，在初级视觉皮层（区域 18）观察到正向 BOLD 信号变化。而在邻近的包含高阶视觉区域的外侧裂上回中检测到了长期的负 BOLD 变化。然而，已知这两个区域的神经元在视觉刺激期间都会增加尖峰活动。在六个空间频率刺激下获得的正负 BOLD 幅度高度相关。负大胆百分比变化大约是正机会的三分之一。具有正 BOLD 信号的区域 18 的 CBV 有所增加。而表现出长期负 BOLD 信号的区域的 CBV 则下降。区域 18 中的 CBV 变化比来自相同相应区域的 BOLD 信号和侧裂上回的 CBV 变化更快。结果支持这样的观点：皮质血液资源的重新分配可以克服神经活动增加引起的局部对脑血流量增加的需求。这项研究的结果表明，将阴性 BOLD 信号解释为神经元活动减少时应谨慎。
Functional magnetic resonance imaging (fMRI) techniques are based on the assumption that changes in spike activity are accompanied by modulation in the blood oxygenation level-dependent (BOLD) signal. In addition to conventional increases in BOLD signals. sustained negative BOLD signal changes are occasionally observed and are thought to reflect a decrease in neural activity. In this study, the source of the negative BOLD signal was investigated using T-2*-weighted BOLD and cerebral blood volume (CBV) techniques in isoflurane-anesthetized cats. A positive BOLD signal change was observed in the primary visual cortex (area 18) during visual stimulation. while a prolonged negative BOLD change was detected in the adjacent suprasylvian gyrus containing higher-order visual areas. However, in both regions neurons are known to increase spike activity during visual stimulation. The positive and negative BOLD amplitudes obtained at six spatial-frequency stimuli were highly correlated. and negative BOLD percent changes were approximately one third of the postitive chances. Area 18 with positive BOLD signals experienced an increase in CBV. while regions exhibiting the prolonged negative BOLD signal underwent a decrease in CBV. The CBV changes in area 18 were faster than the BOLD signals from the same corresponding region and the CBV changes in the suprasylvian gyrus. The results support the notion that reallocation of cortical blood resources could overcome a local demand for increased cerebral blood flow induced by increased neural activity. The findings of this study imply that Caution should be taken when interpreting the negative BOLD signals as a decrease in neuronal activity.