Optimizing the order of operations for movement scrubbing: Comment on Power et al.

A recent study by Power and colleagues shows that BOLD artifacts induced by head movement can substantially alter patterns of resting-state functional connectivity and proposes a novel procedure for reducing these artifacts by deleting (or "scrubbing") movement-contaminated volumes. The authors acknowledge that this work is descriptive and not prescriptive, and note that future studies may refine the proposed scrubbing method. Nevertheless, it is worth pointing out that this method can be improved substantially by a single transposition in the order of operations. Temporal filtering is known to introduce ringing artifacts that emanate from sharp transitions in signal intensity. The method proposed in the target article applies temporal filtering before deleting contaminated volumes in effect, spreading movement-related artifacts backwards and forwards in time, but deleting only the originally contaminated data. Using simulated data, we show that deleting and replacing contaminated volumes before temporal filtering removes a greater proportion of artifactual signal while retaining a greater proportion of the original data. (C) 2011 Elsevier Inc. All rights reserved.