Mild Traumatic Brain Injury, PTSD Share Reduced Memory Function Patterns

Individuals with mild traumatic brain injury (mTBI) and post-traumatic stress disorder (PTSD) have primarily overlapping patterns of reduced resting-state functional connectivity (rsFC) in working memory (WM) regions of the brain, which is consistent with previous neuroimaging and clinical studies, according to study findings published in Brain Research.

Researchers conducted an observational study that comprised 127 US military service members from the San Antonio Military Medical Center who had mTBI only (n=46; 6.5% women), PTSD only (n=24; 12.5% women), and an orthopedically injured (OI) control group (n=57; 19.2% women). Voxelwise rsFC analyses with WM brain regions were conducted to test mTBI vs PTSD differences in WM network connectivity.

Participants in the mTBI group were younger than those in the PTSD group (32.7 years vs 37.4 years) and OI group (37.5 years). There were significant differences between groups in WM performance with lower WM index (WMI) scores for mTBI than participants in the OI group. Participants in the PTSD group also had lower WMI scores than participants in the OI group.

Researchers observed reduced rsFC between ventrolateral prefrontal cortex (vlPFC), lateral premotor cortex, and dorsolateral prefrontal cortex (dlPFC) WM regions and brain regions in the dorsal attention and somatomotor networks in both the mTBI and PTSD groups compared with the control group. Individuals with PTSD had lower rsFC between both the lateral premotor WM seed region and middle occipital gyrus and between the dlPFC WM seed region and paracentral lobule compared with individuals with mTBI. Only vlPFC connectivity was shown to be significantly associated with WM performance across all groups.

In supplementary multiple linear regression analyses, greater mTBI and PTSD symptom severity was associated with reduced rsFC of the left vlPFC and right lateral premotor cortex WM regions. There were no relationships between clinical symptoms and rsFC of the right dlPFC, nor was there an association in the mTBI group between time since brain injury and dlPFC WM regions, lateral premotor cortex, or rsFC of the vlPFC.

Study limitations include using data from 2005, using conflicting WMI scores from different sources, uncertainty about PTSD generalizability of findings, and group differences in rsFC that did not survive Bonferroni correction.

Study authors concluded, “Results from this study generally suggest that both mTBI and PTSD may similarly diminish connectivity of WM regions, in particular prefrontal cortex, which in turn could impair everyday tasks requiring WM. Our results also revealed aberrant connectivity between prefrontal WM regions and brain regions outside the frontoparietal network, indicating that the process of WM may recruit connectivity between WM and non-WM regions to address cognitive demands.”