Background. Increased concussion awareness over the past decades and the development of advanced neuroimaging techniques have led to a rise of studies on the acute and subacute effects of concussion on brain functioning in children and adolescents. The default mode network (DMN), a set of brain regions most active during rest, has been highlighted as one network potentially affected. There is currently a lack of studies looking at long-term post-concussion effects on the DMN and investigating differences in DMN connectivity in youth reporting multiple concussions versus a single concussion. Objective. This research aims to elucidate if long after the injury, youth with multiple concussions present altered DMN functional connectivity in comparison to participants with one concussion or with an orthopedic injury. Methods. Participants (N=57, 27 girls and 30 boys; M=14.7, SD=2.8, range from 8 to 19 years old) were seen on average 31.56 months post-injury (SD=19.4). They were divided in three groups (orthopedic injury and no concussion=20; one concussion=16; multiple concussions=21) and underwent a resting-state functional magnetic resonance imaging (rsfMRI) scan, followed by the completion of the ADHD Rating Scale-5 for Children and Adolescents (parent-report – only inattention score reported) and the Post-Concussion Symptom Inventory (PCSI; self- and parent-report). Anterior and posterior DMN components were extracted from the fMRI data using FSL’s MELODIC. A dual regression resulted in a set of participant-specific spatial maps for each DMN component. We then tested for pairwise group differences using the respective DMN component as a mask in FSL’s Randomise (5000 permutations) and threshold-free cluster enhancement to estimate cluster activation. We then tested for group differences at a threshold of p<0.01 family-wise error corrected (controlling for age, sex, and inattention symptoms). Results. Functional connectivity of the anterior DMN was significantly reduced in the group with multiple concussions (M=3.2 concussions, SD=1.7) compared to the two other groups (single concussion and orthopedic injury) whereas functional connectivity of the posterior DMN was not significantly different between groups. Supplementary analyses also revealed no significant associations between the DMN functional connectivity and PCSI scores for any of the three groups. Conclusions. These results suggest reduced connectivity in the anterior part of the DMN in children and adolescents who had multiple concussions, with no clear links to post-concussive symptoms. This underlines the need for future longitudinal studies using rsfMRI to evaluate DMN changes over time post-injury and to identify predictors of DMN hypoconnectivity in those with multiple prior concussions.

Default mode network functional connectivity after multiple concussions in children and adolescents