Dear SPMers,
I would like to make direct inter-hemispheric comparisons for specific contrasts in my fMRI analysis, e.g. I'd like to analyze whether the left and right hemisphere process specific stimuli differently. To do so, I normalized my functional volumes to a symmetrical template and left-right flipped (x-axis) the smoothed images, including a set of unflipped and flipped volumes in the first-level design. I then created the contrast condition_unflip-condition_flip for my conditions on first-level in order to contrast the difference in hemispheric activation of condition1 and condition2 at the second-level analysis. However, when analyzing condition1>condition2, almost exactly the same (but mirrored) activations result as from the contrast condition2>condition1. It appears to me that this is probably not correct. Any idea what I could have done wrong and how I should do the analysis of inter-hemispheric differences? Any help and suggestions would be appreciated.
Thanks in advance,
Kerstin
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