Influence of study design on effects of mask wearing on fMRI BOLD contrast and systemic physiology - A comment on Law et al. (2021).

In a study by Law and colleagues recently published in Neuroimage, the authors reported that wearing a surgical mask during an fMRI scan leads to a statistically significant subject-specific change (30%) in the baseline BOLD level in gray matter, although the response to a sensory-motor task was unaffected. An average increase in end-tidal CO2 of 7.4% was found when wearing a mask, despite little support in the literature for major effects of mask wearing on blood gas levels. We comment on these findings, point out a several relevant limitations of the study design and provide alternative interpretations of these data.