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DMN文献阅读问题 | Forum of resting-state fMRI

DMN文献阅读问题

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在阅读一篇癫痫默认状态网络的文献中产生了一些问题,望指教,谢谢大家的耐心与时间!
Paper:Altered Functional Connectivity in Default Mode Network in Absence Epilepsy: A Resting-State fMRI Study.
目的:观察癫痫DMN及其内部区域间功能连接的改变。
Data analysis:
1、 DMN Identification: 以PCC的功能连接pattern来定义DMN。
2、 比较患者与对照两组间的DMN功能连接,得出DMN的改变。
3、 Region-wise Functional Connectivity in DMN:比较DMN内区域之间的功能连接。在这一步,想请教各位老师如下问题:
Questions:
1、 For the frontal lobe, however, a very large cluster obviously included four different DMN regions (dorsal medial prefrontal cortex, ventral medial prefrontal cortex, left and right superior frontal gyri). Therefore, it was separated into four nodes. A total of 12 DMN nodes were defined.
该处理将单样本得出的额叶的一个大cluster分为了四个区域,想请教的是,类似这种
情况,通常我们做组间对比得出一个大的Cluster差异区域,报表里面显示有几个区域,怎么去查找这些区域的peak点,进而怎么将这些小区域单独提取出来呢?
2、 Mean time series were extracted by averaging the time series of each peak voxel and its nearest 26 neighbors. The resulting time series were correlated between nodes of each subject, and then an 12×12 correlation matrix for each subject was obtained.
该步骤将DMN内各区的peak点及其周围的26个像素时间序列平均并提取出来,用于区域间的相关分析。请问怎么提取peak点及其周围26个像素的时间序列,这样做是否比提取ROI全部voxel的时间序列更具特征性?
3、 Two-sample two-tailed t-tests were performed on all 66 possible connections represented in the 12×12 correlation matrices between patients and controls. The statistical significance level was set to P<0.05 (FDR-corrected).
问题是这种很多个相关值的对比,多重比较的校正标准应该怎么设?
 
文章再比较区域间功能连接后另作Graph Definition and Visualization,这一步看的挺晕,是否可以帮忙解释解释?
In terms of the probability of the observed zij > Z under the null hypothesis that zij is less than an arbitrary value Z, the threshold Z was defined. Because the multiple, nonindependent tests were for 66 possible connections among the 12 regions, the threshold P < 0.05 (FDR-corrected) was applied for multiple comparison tests. In other words, a layout of undirected edges was shown only under zij > Z for each subject and group.

Re

1. 从这段话来说,看不出作者是怎样对一个大cluster进行分区的。
2. 可能是作者找不到更好的定义ROI的办法,所以采用周围26个体素的办法。个人认为不如使用定义小球的办法。
3. 12X12 矩阵(其中只有12*11/2的有效无素),采用FDR校正是比较常见的方法。
4. 我的理解,12X12 矩阵经FDR校正后,定义为Graph并显示。

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