I have two PPI questions:

1- if I have a PM modulation (e.g. linear changes) and done +1 on the subjects levels and then did group analysis using +1 or -1 ? is this correct (i.e. do I have to return to the subjects level again and do the contrast -1 in order to perform one sample t tests group analysis ? 

Now the PPI related question here is that what does it mean a negative first order linear PPI analysis between ROI (A (seed)) and ROI (B) ? 

2- The second question is related to the group analysis. If I have two groups patients (A) and healthy (B), when performing two sample t tests to investigate PPI (A) > PPI (B) I do not get any significant even at very low threshdol. Is it always difficult to get differences between group and this need very high number of samples ?

Thanks

Aser