Head motion is problematic in task and resting state fMRI studies. Head motion during scans causes image intensity to reflect not only blood oxygenation but also frank motion-related artifact. It is a common practice to align the data throughout a scan by estimating the position of the head in space at each volume. Realignment is an essential part of data processing, but it cannot correct the signal alterations or image distortions that occur as a result of movement. Investigators have demonstrated the utility of a variety of methods for dealing with motion in general linear model (GLM) estimation. We will discuss motion-related artifact and some of the approaches developed to correct it in the context of this paper:
Siegel et al. (2014) Statistical improvements in functional magnetic resonance imaging analyses produced by censoring high-motion data points. Human Brain Mapping 35:1981-1996.