Alteration of brain default network in subacute phase of injury in concussed individuals: Resting-state fMRI study.
Johnson B, Zhang K, Gay M, Horovitz S, Hallett M, Sebastianelli W, Slobounov S. NeuroImage, 2011 Jul; ahead of print.
There are a number of symptoms that are associated with a mild traumatic brain injury (mTBI); however, neuropsychological testing and conventional neuroimaging techniques (e.g., standard magnetic resonance [MR] imaging, computed tomography [CT] scans) are not sensitive enough to detect subtle changes. There have been advances in the neuroimaging field that allow a more sensitive and specific detection of mTBI using functional magnetic resonance imaging (fMRI). This study used resting-state fMRI (rs-fMRI; resting state = individual lying quietly with eyes closed) to assess the connectivity between brain regions in the default mode network (DMN; portions of the brain that continue to work when the body is still awake but resting) of athletes with and without a history of mTBI. Experimental participants were collegiate athletes who recently received an mTBI, but clinically had no sign and symptoms, and were cleared to participate in low-level aerobic activity. Fourteen of these athletes were scanned within 24 hours of their symptoms resolving and 9 extra athletes were scanned after 24 hours since their symptoms resolved (on average 10 days after their symptoms resolved) to determine the influence of multiple mTBI.  The control population was composed of 15 volunteer collegiate athletes who did not have a history of mTBI. The regions of interest were based on the regions of the brain within the DMN as well as those that were previously reported to be influenced by mTBI. The rs-fMRIs depicted that the number and strength (size of synapse and amount of activity at the synapse) of connections in the DMN were altered among the participants with a history of mTBI compared to the controls. The affected areas of the brain consisted of those involving eye targeting for movement (lateral parietal cortex), motor planning and working memory (dorsolateral prefrontal cortex), and awareness (posterior cingulate).  Furthermore, an increased number of reported mTBI was associated with an overall loss of connectivity within the DMN. The authors suggest that these findings indicate that “alterations in the brain resting state default mode network in the subacute phase of injury may be of use clinically in assessing the severity of mTBI and offering some insight into the pathophysiology of the disorder.”
The advancement of neuroimaging is leading to a better understanding and view of the secondary damage within the brain occurring from an mTBI.  The results from this study demonstrated that there were deficits in athletes who had recently obtained an mTBI but were asymptomatic compared to those who had no history of an mTBI. Additional analyses suggested that connectivity decreases as the number of mTBIs increase. However, it is unclear if these differences are long-term or short-term abnormalities. Either way, medical professionals should consider that even at rest and symptom free the brain might not be functioning properly following an mTBI. While the authors suggest this might be an effective way of assessing the severity of mTBI we still need to know if these measures improve after an mTBI as well as how fMRI performs as a diagnostic or prognostic assessment. Future research in this field may influence our return-to-play decisions after brain injuries. In the meantime, medical professionals should adhere to the NCAA guidelines for return-to-play management of mTBIs including a 24-hour sign and symptom free waiting period, as well as restoration measures on cognitive and proprioception tests. After that, medical professionals should use a gradual return to play starting at low-level aerobic activity until full functional return to activity. This study is further proof that being conservative with our return-to-play criteria is probably the safest approach.
Written by: Jane McDevitt
Reviewed by: Jeffrey Driban

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Johnson B, Zhang K, Gay M, Horovitz S, Hallett M, Sebastianelli W, & Slobounov S (2011). Alteration of brain default network in subacute phase of injury in concussed individuals: Resting-state fMRI study. NeuroImage PMID: 21846504