Investigate the relationship of chronic neurobehavioral and cognitive symptoms in military personnel with history of blast-related mild TBI and compare to a well-matched group of combat-deployed controls.

274 participants (mean age=34 years; mean education=14.75 years; 91.2% male) enrolled in the EVOLVE longitudinal study of combat-deployed military personnel were subdivided into those with history of blast TBI (n=165) and controls without history of blast exposure and TBI (n=109). As part of a larger study, we conducted a sub-analysis of 5-year follow up data. We focused on group differences (Mann-Whitney U) and correlational relationships between self-report neurobehavioral symptoms via the Frontal Systems Behavior Scale (FrSBE) and cognitive performances on measures of attention, working memory, processing speed, and executive functioning including D-KEFS Color Word Interference (CWI), Trailmaking A and B, and the Conners Continuous Performance Test (CPT).

The Blast TBI group reported higher levels of neurobehavioral symptoms on the FrSBE (p<.001), including domains of apathy (p<.001), disinhibition (p<.001), and executive dysfunction (p<.001), compared to Controls. On cognitive measures, group differences were observed on CWI Inhibition/Switching (p=.008), Trails B time (p=.010), and CPT commission errors (p=.014), such that the Blast TBI group performed worse than Controls. No significant group differences were observed for CPT omission errors or CPT hit rate (p’s>.05). After adjustment for multiple comparisons, greater FrSBE apathy correlated with slower performance on Trails A for Blast TBI (r=0.22, p=.014) but not Controls. Apathy endorsement was not significantly related to CPT omission errors for either group (p’s>.05). Higher endorsement of disinhibition symptoms was associated with worse performance on CWI Inhibition (Blast TBI: r=-0.19, p=.036; Controls: r=-0.28, p=.012) and Inhibition/Switching (Blast TBI: r=-0.23, p=.010; Controls: r=-0.29, p=.010) conditions for both groups, whereas only the Blast TBI group showed significant relationships between disinhibition symptoms and Trails B-A time (r=0.20, p=.025) and CPT commission errors (r=.18, p=.038). Higher endorsement of executive dysfunction correlated with poorer performance for Trails B-A for both groups (Blast TBI: r=.24, p=.009; Controls: r=.24, p=.030).

Our findings reveal that at 5-year follow up, military personnel with history of blast-related mild TBI reported significantly greater neurobehavioral symptoms and performed lower on standardized measures of executive functioning, relative to combat-deployed controls without TBI or blast exposure. Significant relationships between neurobehavioral symptoms and cognitive performance were present in both groups. However, these relationships were more pronounced in the Blast TBI group, including greater apathy associated with slower visual tracking as well as greater endorsement of disinhibition associated with set-switching. Objective measures of response inhibition were related to disinhibition endorsement for both groups, though impulsive errors were more pronounced for the Blast TBI group. Our results suggest chronic cognitive and neurobehavioral symptoms are present in military personnel with history of blast TBI exposure, and also discrepant from a well-matched control group of combat deployed military personnel. Future studies of this population should explore models to predict cognitive performance from neurobehavioral symptoms in military personnel, as this could inform treatment approaches for those at greatest risk of cognitive change.