The effect of wearing a tight FFP2/KN95 facemask on brain functional connectivity was significant using the SN but not the DMN, sensorimotor, visual, dorsal attention or language networks as seed regions. Importantly, there were no potentially confounding physiological effects since no group differences were found in heart rate or respiration.
The only previous study available in this field 1 specifically assessed the effect of wearing a facemask on functional MRI but with a different approach and objective. This study assessed task-related fMRI during a basic sensory-motor task designed to activate visual, auditory, and sensorimotor cortices in 8 participants. This study did not report significant effects of wearing a facemask on task-related fMRI activation in basic sensorimotor areas. We expected only very subtle changes related to wearing a facemask and those changes to occur in higher-level cognitive centers. The current resting-state fMRI study in 23 cases focusing on higher-level resting networks found significant effects only related to the high-level SN. Of note, and consistent with a previous study 1, our analysis did not reveal significant differences using the lower-level sensorimotor or visual networks as seed regions.
We expected only very subtle changes related to wearing a facemask, and those changes to occur were related to higher-level cognitive centers. In agreement with our a priori hypothesis, the effect of facemask wearing was confined to an interaction between the SN as the seed region and the left middle frontal and precentral gyrus. The SN is thought to facilitate the detection of important environmental stimuli 2,5. It is mainly involved in detecting and filtering multimodal salient stimuli and mediating the transition from the DMN to the central executive network. Our results might imply that the wearing of a facemask might impact our ability to detect and react appropriately to salient stimuli by altering the functional connectivity of the SN. However, this phenomenon concerned only the connections to the left frontal and precentral gyrus. The significance of this finding remains unclear. Altered functional connectivity of the SN with frontal and precentral areas was reported as part of a more global cortical disconnection in a variety of neuropsychiatric disorders, including psychosis, poststroke depression and attention deficit syndrome 6–8. In young controls, the connectivity between the SN and left frontal as well as precentral areas is thought to be crucial not only for episodic memory skills 9 but also for working memory activation 10. Whether changes in restricted parts of SN functional connectivity may predispose individuals to decreased activation of these cognitive functions in highly demanding situations is still unknown.
Two limitations should be considered when interpreting the present findings. To avoid the well documented gender-related differences in functional connectivity 11, we included only male participants in this study. Although this procedure makes sense given the small series of cases that accepted this constraining experimental design, it naturally limits the generalizability of the present findings. Moreover, we deliberately used a tight FFP2/KN95 facemask, which many people prefer in the context of the COVID-19 pandemic and are requested by most airline companies. We would expect smaller effects on brain functional connectivity when using less tight surgical facemasks, which was the standard facemask in the field of medicine before the COVID-19 pandemic. Future studies with various types of masks in mixed samples and using ad hoc activation paradigms will make it possible to complete these at rest observations, gaining better insight into the impact of facemask wearing on brain activation patterns.