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):

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).

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