Default-mode network disruption in mild traumatic brain injury

Abstract

Purpose: To investigate the integrity of the default-mode network (DMN) by using independent component analysis (ICA) methods in patients shortly after mild traumatic brain injury (MTBI) and healthy control subjects, and to correlate DMN connectivity changes with neurocognitive tests and clinical symptoms.

Materials and methods: This study was approved by the institutional review board and complied with HIPAA regulations. Twenty-three patients with MTBI who had posttraumatic symptoms shortly after injury (<2 months) and 18 age-matched healthy control subjects were included in this study. Resting-state functional magnetic resonance imaging was performed at 3 T to characterize the DMN by using ICA methods, including a single-participant ICA on the basis of a comprehensive template from core seeds in the posterior cingulate cortex (PCC) and medial prefrontal cortex (MPFC) nodes. ICA z images of DMN components were compared between the two groups and correlated with neurocognitive tests and clinical performance in patients by using Pearson and Spearman rank correlation.

Results: When compared with the control subjects, there was significantly reduced connectivity in the PCC and parietal regions and increased frontal connectivity around the MPFC in patients with MTBI (P < .01). These frontoposterior opposing changes within the DMN were significantly correlated (r = -0.44, P = .03). The reduced posterior connectivity correlated positively with neurocognitive dysfunction (eg, cognitive flexibility), while the increased frontal connectivity correlated negatively with posttraumatic symptoms (ie, depression, anxiety, fatigue, and postconcussion syndrome).

Conclusion: These results showed abnormal DMN connectivity patterns in patients with MTBI, which may provide insight into how neuronal communication and information integration are disrupted among DMN key structures after mild head injury.

© RSNA, 2012.

Figures

Figure 1:

DMN templates created with the seed-based method in healthy control subjects. A, PCC-seed–based template, with predominant PCC, bilateral inferior parietal, and MPFC connectivity (corrected, P < .05; cluster size, K ≥ 20). B, MPFC-seed–based template shows predominant MPFC connectivity with PCC nodes detected (corrected, P < .05; cluster size, K ≥ 20). C, Binarized image of combined-network seeding from the MPFC and PCC show a more inclusive connectivity pattern of the DMN.

Figure 2:

Group t test maps of single-subject ICA results and comparison between patients with MTBI and control subjects. When compared with DMN patterns in the control group (A), the patient group (B) showed significantly decreased connectivity in the posterior portion (arrowheads) and increased connectivity in the anterior portion (arrows) of the DMN (P < .01; cluster size, K ≥ 20). C, The group-level voxelwise image of single-participant DMN pattern comparing MTBI to control groups shows decreased connectivity regions in blue and increased connectivity regions in yellow.

Figure 3:

Plot of patients with MTBI shows that increased functional connectivity (z scores) in the MPFC region correlates negatively (r = −0.44, P = .03) with decreased functional connectivity (z scores) in the PCC and parietal regions, which may suggest a highly complementary and dynamically equilibratory relationship between the two key substructures of the DMN in terms of function after injury. fcMRI = functional connectivity MR imaging.

Figure 4:

DMN templates obtained with the hybrid ICA seed method in patients and control subjects (corrected, P < .05; K ≥ 20). A, Typical but enhanced connectivity pattern of the DMN was identified in the healthy control group. B, Disrupted DMN pattern is shown in the patient group. C, Group-level voxelwise image of hybrid DMN template differences comparing MTBI to control groups. Red = increased functional connectivity, blue = decreased functional connectivity in patients compared with control subjects. These changes in DMN pattern were consistent with the single-subject ICA results by means of visual inspection.

Figure 5:

Plots show correlation analyses after Bonferroni correction between neuropsychologic tests and single-subject ICA z images in patients with MTBI. A, Pearson correlation analysis shows significant positive correlation (r = 0.60, P = .02) between functional connectivity in posterior regions and Trail Making Test B z score. B, Spearman rank correlation shows significant negative correlation (r = −0.56, P = .01) between functional connectivity of the anterior MPFC and depression scores in patients with MTBI.