Sports Medicine Research: In the Lab & In the Field: Hard to Make Connections after a Concussion?….Blame it on the Default-Mode Network (Sports Med Res)
Monday, January 7, 2013

Hard to Make Connections after a Concussion?….Blame it on the Default-Mode Network

Default-mode network disruption in mild traumatic brain injury

Zhou Y., Milham MP., Lui YW., Miles L., Raume J., Sodickson DK., et al. Radiology. 2012; 265(3): 882-892.

The default-mode network comprises several brain regions (i.e., posterior cingulate cortex, inferior parietal and medial prefrontal cortex) and is involved in brain activity at rest. When this network is altered higher cognitive functions (e.g., memory) become disrupted. Similar dysfunctions are symptoms from a mild traumatic brain injury (MTBI). Therefore, Zhou and colleagues investigated the integrity of the default-mode network among 23 patients with MTBI and 18 healthy control participants. Furthermore, they tested if changes in connectivity within the default-mode network were associated with neurocognitive tests and clinical symptoms. The authors used functional magnetic resonance imaging to determine connectivity of the default-mode network. Then, the participants completed several neuropsychological tests to evaluate cognitive functioning. The battery of tests included the Symbol Digit Modalities (processing speed), Trail Making Test B (mental flexibility), and California Verbal Learning Test II (immediate and delayed verbal memory and verbal learning). In addition, posttraumatic symptoms were self-scored on a Likert scale, the Beck Depression Inventory was used to assess depressive symptoms, and the Fatigue Severity Scale measured fatigue. The MTBI group showed decreased connectivity within the posterior cingulate cortex and the parietal regions compared to the healthy control group. Additionally, the MTBI group also demonstrated increased connectivity in the anterior medial prefrontal cortex compared to healthy controls. These fronto-posterior opposing changes within the default-mode network were related. Furthermore, the reduced connectivity within the posterior regions correlated with the poorer scores on the Trail Making Test B (the participant’s mental flexibility). The increased frontal and medial prefrontal cortex connectivity correlated with worse posttraumatic symptoms (i.e., depression, anxiety, fatigue, and postconcussion syndrome).

The authors found that patients with MTBI had different connectivity within the default-mode network than healthy participants and that activity within these regions were related to clinical outcomes. Observing relationships between the default-mode network and neurocognitive dysfunction as well as clinical symptoms provide vital information regarding the pathophysiology of MTBI. For example, the increased activity within the anterior medial prefrontal cortex has previously been shown to be involved in neuronal neuroplasticity  (the brain’s ability to regain connections) recovery and repair, which would be necessary for injured neurons to increase activity to repair connectivity in someone with an MTBI. Abnormal increases in the medial prefrontal cortex have been associated with depression, anxiety, and fatigue, which may explain the correlation with this part of the brain and the posttraumatic symptoms. This information is important in determining which structures and connections are affected after an MTBI and could further define how to care for a patient following an MTBI. Do you think functional magnetic resonance imaging could eventually help diagnosis MTBI as well as monitor the disease progression and recovery of an MTBI? Do you think tests for mental flexibility (Trail Making Test B) should be a part of a concussion evaluation?

Written by: Jane McDevitt MS, ATC, CSCS
Reviewed by: Jeffrey Driban

Related Posts:
Zhou Y, Milham MP, Lui YW, Miles L, Reaume J, Sodickson DK, Grossman RI, & Ge Y (2012). Default-mode network disruption in mild traumatic brain injury. Radiology, 265 (3), 882-92 PMID: 23175546

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