Why motion correction first? fmriprep

Hi all, I was wondering why fmriprep has implemented motion correction before slice timing correction, if one opts to do slice timing. There’s some contention in the literature about whether motion correction or slice timing should be first, and I was wondering what the rationale is for fmriprep to implement motion correction first.

(I do know that output motion parameters are computed before slice timing, according to recommendations of J Power, which is great).

Thank you.

Motion correction is performed after slice-timing correction, but using parameters that were calculated before slice-timing correction. All transforms (apart from STC) are applied in a single shot, to reduce artifacts, so it would actually be very difficult to perform HMC before STC.