Restom Khaled, Perthen Joanna E, Liu Thomas T
Department of Radiology, University of California San Diego, La Jolla, CA 92093-0677, USA.
Neuroimage. 2008 May 1;40(4):1495-502. doi: 10.1016/j.neuroimage.2008.01.038. Epub 2008 Feb 4.
Prior measures of the blood oxygenation level-dependent (BOLD) and cerebral blood flow (CBF) responses to a memory-encoding task within the medial temporal lobe have suggested that the coupling between functional changes in CBF and changes in the cerebral metabolic rate of oxygen (CMRO(2)) may be tighter in the medial temporal lobe as compared to the primary sensory areas. In this study, we used a calibrated functional magnetic resonance imaging (fMRI) approach to directly estimate memory-encoding-related changes in CMRO(2) and to assess the coupling between CBF and CMRO(2) in the medial temporal lobe. The CBF-CMRO(2) coupling ratio was estimated using a linear fit to the flow and metabolism changes observed across subjects. In addition, we examined the effect of region-of-interest (ROI) selection on the estimates. In response to the memory-encoding task, CMRO(2) increased by 23.1+/-8.8% to 25.3+/-5.7% (depending upon ROI), with an estimated CBF-CMRO(2) coupling ratio of 1.66+/-0.07 to 1.75+/-0.16. There was not a significant effect of ROI selection on either the CMRO(2) or coupling ratio estimates. The observed coupling ratios were significantly lower than the values (2 to 4.5) that have been reported in previous calibrated fMRI studies of the visual and motor cortices. In addition, the estimated coupling ratio was found to be less sensitive to the calibration procedure for functional responses in the medial temporal lobe as compared to the primary sensory areas.
先前对内侧颞叶内记忆编码任务的血氧水平依赖（BOLD）和脑血流量（CBF）反应的测量表明，与初级感觉区域相比，内侧颞叶中CBF的功能变化与脑氧代谢率（CMRO₂）变化之间的耦合可能更紧密。在本研究中，我们使用校准功能磁共振成像（fMRI）方法直接估计与记忆编码相关的CMRO₂变化，并评估内侧颞叶中CBF与CMRO₂之间的耦合。使用对各受试者观察到的血流和代谢变化的线性拟合来估计CBF-CMRO₂耦合比。此外，我们研究了感兴趣区域（ROI）选择对估计值的影响。对记忆编码任务的反应中，CMRO₂增加了23.1±8.8%至25.3±5.7%（取决于ROI），估计的CBF-CMRO₂耦合比为1.66±0.07至1.75±0.16。ROI选择对CMRO₂或耦合比估计值均无显著影响。观察到的耦合比显著低于先前对视觉和运动皮层进行校准fMRI研究中报告的值（2至4.5）。此外，与初级感觉区域相比，发现估计的耦合比对内侧颞叶功能反应的校准程序不太敏感。
