Hi,
Suppose I have 2 main regressors [i.e., two task conditions, say, visual stimulation (V) and auditory stimulation (A)], and my GLM design matrix have four contrasts: (1) [1 0], (2) [0 1], (3) [1 -1], and (4) [-1 1]. I want to know which brain region's functional connectivity with a seed region is increased during V than during A and vice versa, that is, PPI contrasts [1 -1] and [-1 1]. I then perform PPI.
Before that, I try to extract the eigenvariate time series of the seed region. But, among (1)-(4), which contrast should I select to extract VOI? I wonder whether the 4 different contrasts will yield different time course for the seed region.
Thank you. Mike
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