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Abstract
<p class="first" id="P1">Integrity of the default mode network (DMN) is believed to
be essential for human
consciousness. However, the effects of acute severe traumatic brain injury (TBI) on
DMN functional connectivity are poorly understood. Furthermore, the temporal dynamics
of DMN reemergence during recovery of consciousness have not been studied longitudinally
in patients with acute severe TBI. We performed resting-state functional magnetic
resonance imaging (rs-fMRI) to measure DMN connectivity in 17 patients admitted to
the intensive care unit (ICU) with acute severe TBI and in 16 healthy control subjects.
Eight patients returned for follow-up rs-fMRI and behavioral assessment six months
post-injury. At each time point, we analyzed DMN connectivity by measuring intra-network
correlations (i.e. positive correlations between DMN nodes) and inter-network anticorrelations
(i.e. negative correlations between the DMN and other resting-state networks). All
patients were comatose upon arrival to the ICU and had a disorder of consciousness
(DoC) at the time of acute rs-fMRI (9.2 +/- 4.6 days post-injury): 2 coma, 4 unresponsive
wakefulness syndrome, 7 minimally conscious state, and 4 post-traumatic confusional
state. We found that, while DMN anticorrelations were absent in patients with acute
DoC, patients who recovered from coma to a minimally conscious or confusional state
while in the ICU showed partially preserved DMN correlations. Patients who remained
in coma or unresponsive wakefulness syndrome in the ICU showed no DMN correlations.
All eight patients assessed longitudinally recovered beyond the confusional state
by 6 months post-injury and showed normal DMN correlations and anticorrelations, indistinguishable
from those of healthy subjects. Collectively, these findings suggest that recovery
of consciousness after acute severe TBI is associated with partial preservation of
DMN correlations in the ICU, followed by long-term normalization of DMN correlations
and anticorrelations. Both intra-network DMN correlations and inter-network DMN anticorrelations
may be necessary for full recovery of consciousness after acute severe TBI.
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