Hello,
I am having some trouble figuring out higher-level analysis and would appreciate any comments.
Experiment:
n=15, scanning before and after stress.
1. All subjects underwent block design fMRI with 1 rest condition and 1 task condition (e.g. relax, pulse your hand, relax, pulse your hand, ...).
2. All subjects underwent stress outside of MR scanner.
3. All subject underwent fMRI identical to step 1.
We want to know what areas of the brain increase and what areas decrease in activation as well as what areas increase and what areas decrease in deactivation between step 1 and step 3. Seems simple.
Processing so far:
1. All subjects' data at both time points processed using First-level analysis with 1 original EV and 2 contrasts of weights [1] and [-1], respectively. The first contrast indicates activation and the second indicates deactivation when performing the task compared with the rest condition. After processing, each subject has a folder with 2 copes: activation and deactivation.
2. For Higher-level analysis, all subjects scans from step 1 are loaded up in inputs 1-15 and all subjects scans from step 3 are loaded up in inputs 16-30. Both lower-level copes are checked for analysis. FLAME 1+2 and automatic outlier de-weighting are used. The model setup wizard is opened and the option for two groups, paired, is chosen. The calculation is run.
Interpretation:
After processing, in the report I click Results and have two options : Lower-level contrast 1 (Positive), and Lower-level contrast 2 (Negative). If I look at the results for Lower-level contrast 1, there are 2 maps, one for C1 (condition A>B) and one for C2 (condition B>A). C1 has nothing and C2 has some stuff. Great.
If I go back and click on Lower-level contrast 2 (Negative), the map for C1 (condition A>B) is identical to C2 in Lower-level contrast 1, and C2 have no findings (identical to C1 in Lower-level contrast 1).
Questions:
1. Why?
2. How do I tease out what is a positive or negative change in activation or a positive or negative change in deactivation between steps 1 and 3?
Any help is greatly appreciated. Thanks,
Jason
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