after checking a few subjects in my latest data set, I found that the global mean of an EPI time series (computed with spm_global) changes significantly after spatial preprocessing (i.e. plain realignment). Attached is an example: While slice timing changes the time series only very subtly, both realignment and realign&unwarp change the pattern significantly (i.e. they alleviate some of the spiking ripples, while introducing others at different time points.) Any comments or explanations for this are greatly appreciated.