Hi all,
I've a quick question about an fMRI design. We have an experiment starts with a 5 minutes baseline (B) and followed by a 2 minutes stimulus (active_phase_1), then 2 minutes baseline (B2), 2 minutes stimulus (active_phase_2), 2 minutes baseline (B3), 2 minutes stimulus (active_phase_3 the same as active_phase_1) and 2 minutes baseline (B4).
( B-A1-B2-A2-B3-A3-B4 )
We have an assumption that the BOLD doesn't return to the baseline value after the active phases immediately and thus alters the baselines after the first active phase. Moreover the A1/A3 and A2 stimuli are different. In pilot studies we've observed that the baseline value after such stimulus isn't the same as before for more than 90 seconds after the stimulus ended. So we decided that we use separate EVs for every 2 minutes baseline. We have 6 regressors, one for every 2 minutes baseline ( B2, B3, B4 ) and one for every active phases ( A1, A2, A3 ). We do not assign any contrasts for the B2, B3, B4 EVs. We are interested only in the following contrasts ( A1-B, A2-B, A3-B, A2-A1, A1-A3, A2-A3 ). Is it correct in this case to regress out the three other baselines ( B2, B3, B4 ) ?
Thanks a lot,
Gábor
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