Recovery of resting brain connectivity ensuing mild traumatic brain injury

Abstract

Brains reveal amplified plasticity as they recover from an injury. We aimed to define time dependent plasticity changes in patients recovering from mild traumatic brain injury (mTBI). Twenty-five subjects with mild head injury were longitudinally evaluated within 36 h, 3 and 6 months using resting state functional connectivity (RSFC). Region of interest (ROI) based connectivity differences over time within the patient group and in comparison with a healthy control group were analyzed at p < 0.005. We found 33 distinct ROI pairs that revealed significant changes in their connectivity strength with time. Within 3 months, the majority of the ROI pairs had decreased connectivity in mTBI population, which increased and became comparable to healthy controls at 6 months. Within this diffuse decreased connectivity in the first 3 months, there were also few regions with increased connections. This hyper connectivity involved the salience network and default mode network within 36 h, and lingual, inferior frontal and fronto-parietal networks at 3 months. Our findings in a fairly homogenous group of patients with mTBI evaluated during the 6 month window of recovery defines time varying brain connectivity changes as the brain recovers from an injury. A majority of these changes were seen in the frontal and parietal lobes between 3 and 6 months after injury. Hyper connectivity of several networks supported normal recovery in the first 6 months and it remains to be seen in future studies whether this can predict an early and efficient recovery of brain function.

Keywords: brain plasticity; hyper connectivity; longitudinal study; mild traumatic brain injury; resting state functional connectivity; time varying changes.

Figure 1

Group level independent component maps. (A) Lingual gyrus, (B) left frontal parietal network, (C) Salience network, (D) default mode network, (E) motor network, (F) posterior default mode network, (G) higher visual cortex, (H) Dorsal attention network, (I) Inferior frontal gyrus, (J) Fronta-parietal network, (K) Insular network, (L) cerebellum network, (M) pre-central gyrus, (N) basal ganglia, (O) temporal gyrus network.

Figure 2

Group level RSFC differences during recovery from mTBI within 36 h (Control > R1), at 3 months (R2 > R1), and at 6 months (R3 > R2). The decreased connectivity is depicted as edges. The nodes, which are numbered, depicts the ROI seed pairs. Progressively increasing connectivity shown as red edges is most evident at 6 months.

Figure 3

Group level differences observed in the RSFC within mild TBI subjects during recovery. (A) Mean correlation matrices for each of the groups, (B) ROI pairs showing differences in the connectivity within mild TBI (p < 0.005), (C) mean connectivity strength for each of the ROI pair showing differences during recovery in mild TBI subjects.

Figure 4

Group level differences observed in the RSFC between healthy controls and TBI subjects during recovery. (A) Mean correlation matrices for each of the groups, (B) ROI pairs showing differences in the connectivity between HC and mild TBI (p < 0.005), (C) mean connectivity strength for each of the ROI pair showing differences between the HC and mTBI subjects.

Figure 5

Correlation between various behavior scores and the RSFC strength for the ROI pairs showing differences between CTRL and mild TBI as well as within mild TBI group. Correlation matrices show the correlation between each possible pairs. Significant linear correlations are highlighted by a circle (p < 0.01).