Default mode network in concussed individuals in response to the YMCA physical stress test.

We hypothesize that the evolution of mild traumatic brain injury (mTBI) may be related to differential effects of a concussive blow on the functional integrity of the brain default mode network (DMN) at rest and/or in response to physical stress. Accordingly, in this resting-state functional magnetic resonance imaging (fMRI) study, we examined 14 subjects 10±2 days post-sports-related mTBI and 15 age-matched normal volunteers (NVs) to investigate the possibility that the integrity of the DMN is disrupted at the resting state and/or following the physical stress test. First, all mTBI subjects were asymptomatic based upon clinical evaluation and neuropsychological (NP) assessments prior to the MRI session. Second, the functional integrity within the DMN, a main resting-state network, remained resilient to a single concussive blow. Specifically, the major regions of interest (ROIs) constituting the DMN (e.g., the posterior cingulate cortex [PCC]/precuneus area, the medial prefrontal cortex [MPFC], and left and right lateral parietal cortices [LLP and RLP]) and the connectivity within these four ROIs was similar between NVs and mTBI subjects prior to the YMCA physical stress test. However, the YMCA physical stress test disrupted the DMN, significantly reducing the magnitude of the connection between the PCC and left lateral parietal ROI, and PCC and right lateral parietal ROI, as well as between the PCC and MPFC in mTBI subjects. Thus while the DMN remained resilient to a single mTBI without exertion at 10 days post-injury, it was altered in response to limited physical stress. This may explain some clinical features of mTBI and provide some insight into its mechanism. This important finding should be considered by clinical practitioners when making decisions regarding return-to-play and clearing mTBI athletes for sports participation.