Hemodynamic changes after visual stimulation and breath holding provide evidence for an uncoupling of cerebral blood flow and volume from oxygen metabolism.
Hemodynamic changes after visual stimulation and breath holding provide evidence for an uncoupling of cerebral blood flow and volume from oxygen metabolism.
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DOI：
10.1038/jcbfm.2008.109
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发表时间：
2009-01
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--
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功能性神经影像学最常使用血氧水平依赖（BOLD）方法进行，该方法对脑血流量（CBF）、脑血容量（CBV）和脑氧代谢率（CMRO2）的变化敏感。然而，神经元活动激发血流动力学反应的确切机制仍然存在争议。在这里，独立的视觉刺激（14秒闪烁棋盘）和屏气（4秒呼气+14秒屏气）实验平行进行健康志愿者使用BOLD，CBV加权（CBVw）和CBF加权（CBFw）的功能磁共振成像。在视觉刺激后，BOLD信号持续33±5s（n=9），并且是具有负分量（下冲）的双相信号，而CBV和CBF分别在20±5s和20±3s返回基线而没有下冲。屏气后，BOLD信号与CBV（21± 6 s）和CBF（18± 3 s）同时（p>0.05）恢复至基线（23± 7 s），无刺激后下冲。这些数据表明，在视觉激活后，BOLD下冲可能是由于CMRO2持续升高。此外，当CBF和CBV恢复到基线水平时，发现CMRO2持续升高，这为CBV和CBF反应与CMRO2变化的解偶联提供了证据。持续升高的CMRO2神经元活动升高可能是必要的逆转兴奋性突触后电流引起的神经递质运动。
Functional neuroimaging is most commonly performed using the blood-oxygenation-level-depend (BOLD) approach, which is sensitive to changes in cerebral blood flow (CBF), cerebral blood volume (CBV), and the cerebral metabolic rate of oxygen (CMRO2). However, the precise mechanism by which neuronal activity elicits a hemodynamic response remains controversial. Here, separate visual stimulation (14s flashing checkerboard) and breath-hold (4s exhale + 14s breath-hold) experiments were performed in parallel on healthy volunteers using BOLD, CBV-weighted (CBVw) and CBF-weighted (CBFw) fMRI. Following visual stimulation, the BOLD signal persisted for 33±5s (n=9) and was bi-phasic with a negative component (undershoot), whereas CBV and CBF returned to baseline without an undershoot at 20±5s and 20±3s, respectively. Following breath-hold, the BOLD signal returned to baseline (23±7s) at the same time (p>0.05) as CBV (21±6s) and CBF (18±3s), without a post-stimulus undershoot. These data indicate that following visual activation, the BOLD undershoot is likely due to continued elevated CMRO2. Furthermore, persisting elevated CMRO2 is found when CBF and CBV have returned to baseline levels, providing evidence for an uncoupling of CBV and CBF responses from CMRO2 changes. Persisting elevated CMRO2 following elevated neuronal activity may be necessary to reverse neurotransmitter movements arising from excitatory postsynaptic currents.
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