Dear M. Guo,

I don't know if it makes sense to pick up on that thread after 6 months, but I believe I (finally) have an explanation for your observations. In NIAK release 0.6.4.3, the data are resampled in the stereotaxic space (with a non-linear transformation) after high-pass filtering. It seems that this operation can induce slow time drifts back in the time series. I would expect these fluctutations to impact a minority of time series, but you may want to re-filter the data. In the next release of NIAK (0.7) the resampling will be done at the same time as motion correction (SPM-style), and the filtering operations will be performed in stereotaxic space following resampling. Other preprocessing steps will also be added (most notably the scrubbing of time frames showing excessive motion, as described in Power Neuroimage 2012). We will make a new release of the ADHD200 preprocessed data at this time. 

Sorry for the inconvenience. Best regards,

Pierre Bellec