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Dear Paul, The underlying assumption of the SPM imaging source analysis is that the same areas are activated in all conditions but to different degree. If that is not true for your data perhaps you should try a different method. I would try group inversions with all subjects or individual inversions for each subject. Two group inversions are really biasing your analysis toward finding differences so it's not a good idea. Also you can try using IID or COH options which are not as focal. Best, Vladimir On Fri, Jan 13, 2012 at 5:20 AM, Paul Sowman <[log in to unmask]> wrote: > I am comparing sources from two groups: patients vs controls. If it is hypothesized that the two groups have different activation patterns on the same task should I be using group inversion? I.e. if I include all subjects (patients and controls) in the group inversion and then compare between groups will I lose the difference. I assume it is bad to do separate group inversions (one for controls and one for patients) and then compare? > > Thanks, Paul