Dear SPM Experts,
I need help building a statistical analysis in SPM8. I know exactly what I want to do, but there seem to be a lot of different ways of doing it.
Here's the plot: Of 40 subjects of different age groups (Age 8 to 18) I have activation images (.nii) of an oddball task, generated by 3D source reconstruction of EEG files. They all did the same oddball task in the evening and in the morning, after sleep.
In earlier studies my research group found that the GMFP in such a task decreases over night, so now I wanted to test if the involved areas also decrease over night.
My first idea was to use imCalc to subtract the morning-images from the evening-images, but I encountered the problem, that the areas involved in solving the task differ in differerent age groups, so of course those differential images also show different voxels involved.
So even though I find a greater neuronal response in the evening in all subjects, it makes no sense to t-test the differential images, since the remaining activation is in different voxels.
The next idea was to define ROIs of the same size in all differential images (evening minus morning) and average the activation therein. Does this make sense? What functions of the fMRI part of SPM8 is able to do this?
Apart from this, as I am primarily interested in activation of frontal regions, is it necessary to cut away the rest of the activation, for exmaple by using MarsBaR? Or is there a tool in SPM8 wherein I can set all areas I'm not interested in to zero?
Another idea was to simply use a two-paired dependant t-test using both morning and evening images, but I think this won't get me any information about the decrease of activation that happened over night.
Also, I'd be interested if the decrease of activation (or of involved clusters, respectively) changes with age. How should this be done? Do I have to use the differential images or can I work with the images of evening and morning?
Any hints, solutions and clues are greatly appreciated.
Thank you,
Urs Bachofner
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