Wearing a facemask in professional settings is a usual procedure mainly for surgical purposes. The COVID-19 pandemic rendered the long-term use of facemasks a daily reality for the vast majority of citizens. This was the case in professional and even private interactions but also in MRI scanning facilities. This practice was widely accepted and well tolerated to limit the propagation of the virus mainly in vulnerable groups. Under normal conditions and mild exercise, wearing a facemask does not affect sensorial processing, motor or high-level cognitive performances (Morris et al., 2020; Slimani et al., 2021; Wells et al., 2023). However, some lines of evidence indicated that facemasks may alter concentration and visual attention in maximal running aerobic tests (Slimani et al., 2021). By impacting social interaction, facemasks modify the neural responses to recognition of facial cues but also pivotal human abilities serving our daily behavior such as emotion recognition that stimulate empathic responses, perceived closeness, trust attribution and even re-identification of unmasked faces (Ferrari et al., 2021; Grundmann et al., 2021; Marini et al., 2021, 2022; Proverbio and Cerri, 2022; Tsantani et al., 2022; Proverbio et al., 2023). In contrast to behavioral changes, data on the effect of wearing a facemask on brain activation remain rare. Two previous studies indicated that this practice has a subtle but still significant effect on cerebral blood flow and oxygen saturation but also BOLD (blood oxygenation level dependent) baseline signals. This BOLD effect is the basis of functional MRI. In short, local neuronal activity is associated with increased demands on oxygen and associated with a local vascular response which in turn modifies the local concentration ratio of oxygenated versus deoxygenated hemoglobin. This modifies the local magnetic properties that can be assessed using a dedicated MRI pulse sequence. The BOLD response is therefore an indirect vascular response that can be measured in fMRI. In a previous study, we also reported a small yet significant alteration in at rest functional connectivity limited to higher-level salience network in an independent sample of community-dwelling healthy controls (Haller et al., 2022). Functional connectivity fMRI is based on the principle assumption that if spontaneous fluctuations in the BOLD signal in two regions are not random but correlated, then these two regions are probably functionally connected. The more similar the BOLD signal fluctuations over time in two regions, i.e., the higher the correlation between two regions, the more likely is the functional connectivity between them. This study included only at rest fMRI analysis and cannot thus define whether brain activation during highly demanding cognitive tasks may be affected by wearing a facemask. To address this issue, we performed a cross-sectional study comparing the behavioral and fMRI patterns when wearing or not a tight KN95/FFP2 facemask during the performance of a 2-back working memory task in healthy controls. The 2-back working memory task is well established for fMRI studies and previously used by our group (Haller et al., 2013, 2014; Sinanaj et al., 2015; Haller et al., 2017; Zanchi et al., 2017). Since we anticipated only subtle effects related to the wearing of a facemask, the selection of the highly demanding 2-back condition, that implies the mobilization of working memory and not only attentional resources, allowed for obtaining the strong and reproducible fMRI activations needed for the detection of small group differences.

The present study shows that wearing a facemask does not impact on both performances and brain activation patterns during a highly demanding 2-back working memory task. From a cognitive viewpoint, this finding is in line with several observations under normal conditions, high temperatures or mild exercise that demonstrated that the wearing of facemask does not or affect minimally the cognitive performances (Morris et al., 2020; Slimani et al., 2021; Wells et al., 2023). Only one study reported deficits in concentration and visual attention in the context of maximal running aerobic tests (Slimani et al., 2021). It is thus likely that, when wearing a facemask, a deleterious effect on cognition can be observed only under condition of motor or emotional stress.

Imaging data relative to the wearing of a facemask remain rare. In a series of 13 young individuals wearing a FFP2 facemask, Fischer et al., reported a 6.5% increase of cerebral blood flow and a 0.9% increase of oxygen saturation measured by transcranial hybrid near-infrared spectroscopy. The first fMRI study available in this field assessed the effect of wearing a facemask on functional MRI focusing on a basic sensory-motor task designed to activate visual, auditory, and sensorimotor cortices in eight middle-aged participants (Law et al., 2021). The authors reported no significant impact of facemask on task-related activation of sensorimotor areas. More recently, we analyzed the functional connectivity in a resting-state fMRI analysis of an independent sample of 23 healthy controls (Haller et al., 2022). This study reported no significant effect of wearing facemask on the functional connectivity of lower-level sensorimotor or visual networks but found a subtle impact on the interaction between the salience network as the seed region and the left middle frontal and precentral gyrus. More recently, Wu et al. examined the amplitude of low frequency fluctuation (ALFF) and functional connectivity at rest in 15 middle-aged healthy subjects wearing a KN95 mask and natural breathing. In contrast to the previous observations, they reported significant increases and decreases of ALFF as well as significant alterations of functional connectivity of posterior cingulate and medial prefrontal areas when wearing masks (Wu et al., 2023). These first fMRI studies in this field were performed with no or no significant cognitive challenge so that it was not possible to comment on a possible deleterious effect of the facemask in highly demanding situations. Because of its implication in numerous cognitive and cognitive-motor tasks, working memory is called upon in a wide range of activities. We decided to focus our analysis on this cognitive function since it is of key importance in daily life interactions and its brain correlates were very well established across the lifespan (Maillet and Rajah, 2014; Andre et al., 2016). Our findings indicate that wearing of the facemask does not change the functional connectivity patterns even when the demand of cognitive resources is high. These observations parallel the preliminary data of Klugah-Brown and collaborators (Klugah-Brown et al., 2022) who examined the effect of simple surgical mask on fMRI activation patterns during finger tapping, emotional face matching, working memory tasks with negative conclusions.

Some limitations should be considered when interpreting the present findings. To avoid the well-documented gender-related differences in functional connectivity (Murray et al., 2021), female participants were not included in this study. Moreover, we deliberately used a tight FFP2/KN95 facemask that has been the standard of reference the COVID-19 pandemic. It is, however, highly unlikely that the wearing of the less tight surgical facemasks led to significant changes in brain activation patterns. Last but not least, one should keep in mind that the 2-back task is a classical paradigm of working memory that involves attention and executive components but not emotional processing. This latter seems to be the most vulnerable domain of human cognition when wearing a facemask (Ferrari et al., 2021; Grundmann et al., 2021; Marini et al., 2021, 2022; Proverbio and Cerri, 2022; Tsantani et al., 2022; Proverbio et al., 2023). Future fMRI studies including tasks of social cognition are warranted to explore whether the wearing of facemask modifies brain activation patterns when dealing with emotional processing in complex environments.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by University of Geneva, Switzerland. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.

M-LM: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal Analysis, Data curation, Conceptualization. SH: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Methodology, Investigation, Formal Analysis, Data curation, Conceptualization. CR: Writing – review & editing, Writing – original draft, Project administration. FH: Writing – review & editing, Writing – original draft, Formal Analysis. PG: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal Analysis, Data curation, Conceptualization.