Institute for Clinical Radiology, Department of Psychiatry & Alzheimer Memorial Center, University of Munich, Marchioninistr. 15, 81377 Munich, Germany.
Neuroimage. 2010 May 15;51(1):280-7. doi: 10.1016/j.neuroimage.2009.12.008. Epub 2010 Mar 12.
Functional MRI (fMRI) of default mode network (DMN) brain activity during resting state is gaining attention as a potential non-invasive biomarker to diagnose incipient Alzheimer's disease. The aim of this study was to identify effects of normal aging on the DMN using different methods of fMRI processing and evaluation.
fMRI was acquired in 17 young and 21 old healthy subjects and the data were analyzed with (a) volumes of interest (VOI)-based signal time course and (b) independent component analyses (ICA). In the first approach, the strength of DMN region inter-connectivity (as expressed with correlation coefficients) was of primary interest, the second method provided a measure of the magnitude of DMN co-activation.
The older subjects exhibited significantly lower DMN activity in the posterior cingulate (PCC, t-test P<.001) as well as a tendency to lower activity in all other DMN regions in comparison to the younger subjects. We found no significant effect of age on DMN inter-connectivity.
Effects of normal aging such as loss of PCC co-activity could be detected by ICA, but not by signal time course correlation analyses of DMN inter-connectivity. This either indicates lower sensitivity of inter-connectivity measures to detect subtle DMN changes or indicate that ICA and time course analyses determine different properties of DMN co-activation. Our results, therefore, provide fundamental knowledge for a potential future use of functional MRI as biomarker for neurodegenerative dementias where diminished DMN activity needs to be reliably differentiated from that observed in health aging.
在静息状态下，默认模式网络 (DMN) 的功能性磁共振成像 (fMRI) 作为诊断早期阿尔茨海默病的潜在非侵入性生物标志物越来越受到关注。本研究的目的是使用不同的 fMRI 处理和评估方法来确定正常衰老对 DMN 的影响。
在 17 名年轻和 21 名健康的老年人中采集 fMRI，并使用 (a) 基于感兴趣区 (VOI) 的信号时程和 (b) 独立成分分析 (ICA) 进行数据分析。在第一种方法中，DMN 区域间连接的强度（用相关系数表示）是主要关注点，第二种方法提供了 DMN 共激活幅度的度量。
与年轻受试者相比，老年受试者在后扣带回 (PCC) 中表现出明显较低的 DMN 活性 (t 检验 P<.001)，并且其他所有 DMN 区域的活性也有降低的趋势。我们没有发现年龄对 DMN 间连接性的显著影响。
通过 ICA 可以检测到正常衰老的影响，如 PCC 共激活的丧失，但不能通过 DMN 间连接的信号时程相关分析来检测。这要么表明连接性测量对检测 DMN 细微变化的敏感性较低，要么表明 ICA 和时程分析确定了 DMN 共激活的不同性质。因此，我们的结果为功能磁共振成像作为神经退行性痴呆的生物标志物的潜在未来应用提供了基本的知识，其中 DMN 活性的降低需要与健康衰老中观察到的活性可靠地区分。
