Dear SPMers,
In my fMRI higher level analysis using simple regression (performed in SPM 5), I found that activations in brain regions A and B to a task were negatively correlated with age. Since gray matter density (GMD) in some brain regions is also negatively correlated with the age, some may argue that reduced activations in both regions may be due to tissue loss rather than BOLD reduction to the task. To prove aging effects on BOLD responses, I have to make correction for GMD loss. As such, I performed another VBM analysis (in VBM 5.1) to get the picture of GMD changes.
My question is, what then should I do to correct BOLD responses for brain tissue loss?
I have 2 ideas but each has something I don’t know how to perform:
(1) In the fMRI higher-level simple regression analysis using age as covariate of interest, use each subject’s VBM data as covariate of no interest, factoring out it’s effect. But how can I do this? How to put each subject’s VBM data (file sm0w….?) in the design matrix?
(2) Produce 2 ROIs from fMRI group analysis representing brain regions A and B. Use them to extract individual VBM data in these 2 regions. In SPSS, perform a partial correlation analysis (variables: BOLD signals in A/B, and age) controlling for regional VBM data. But how can I extract individual VBM data in these 2 regions?
If both are not appropriate, I wonder if other method should be better/correct. Really appreciate for any help!
Carlos
|