Reply to Spreng et al.: Multiecho fMRI denoising does not remove global motion-associated respiratory signals

In 2 human functional magnetic resonance imaging (fMRI) datasets (89 “ME” subjects; 12 “NA” subjects), we used signal decay properties to separate 2 kinds of signals: S0 artifacts, which were spatially specific, and T2* modulations, which occurred over the whole brain (1). We established that whole-brain (global) fMRI signals were nearly unchanged before and after removal of S0 signals. Hence, most global signals are T2* signals, compatible with neural activity or with respiratory-related pCO2 changes. In a dataset with paired respiratory records (NA data), we illustrated that changes in respiratory traces were temporally accompanied by prominent global signal modulations, an association visible in “gray plots” of single scans (2). Across scans, variance in global signals correlated with variance in respiratory measures. Spreng et al. (3) critique our paper, stating that “there is no definitive evidence . . . that respiration effects . . . even substantively contribute . . . to residual global signal [following removal of S0 … [↵][1]1To whom correspondence may be addressed. Email: jdp9009{at}nyp.org. [1]: #xref-corresp-1-1