Neural Activation during Response Inhibition Differentiates Blast from Mechanical Causes of Mild to Moderate Traumatic Brain Injury

Abstract

Military personnel involved in Operations Enduring Freedom and Iraqi Freedom (OEF/OIF) commonly experience blastinduced mild to moderate traumatic brain injury (TBI). In this study, we used task-activated functional MRI (fMRI) to determine if blast-related TBI has a differential impact on brain activation in comparison with TBI caused primarily by mechanical forces in civilian settings. Four groups participated: (1) blast-related military TBI (milTBI; n = 21); (2) military controls (milCON; n = 22); (3) non-blast civilian TBI (civTBI; n = 21); and (4) civilian controls (civCON; n = 23) with orthopedic injuries. Mild to moderate TBI (MTBI) occurred 1 to 6 years before enrollment. Participants completed the Stop Signal Task (SST), a measure of inhibitory control, while undergoing fMRI. Brain activation was evaluated with 2 (mil, civ) · 2 (TBI, CON) analyses of variance, corrected for multiple comparisons. During correct inhibitions, fMRI activation was lower in the TBI than CON subjects in regions commonly associated with inhibitory control and the default mode network. In contrast, inhibitory failures showed significant interaction effects in the bilateral inferior temporal, left superior temporal, caudate, and cerebellar regions. Specifically, the milTBI group demonstrated more activation than the milCON group when failing to inhibit; in contrast, the civTBI group exhibited less activation than the civCON group. Covariance analyses controlling for the effects of education and selfreported psychological symptoms did not alter the brain activation findings. These results indicate that the chronic effects of TBI are associated with abnormal brain activation during successful response inhibition. During failed inhibition, the pattern of activation distinguished military from civilian TBI, suggesting that blast-related TBI has a unique effect on brain function that can be distinguished from TBI resulting from mechanical forces associated with sports or motor vehicle accidents. The implications of these findings for diagnosis and treatment of TBI are discussed.

MR Imaging Applications in Mild Traumatic Brain Injury: An Imaging Update

“…These discrepant findings may illustrate challenges inherent to the study of mTBI, where there exists heterogeneity in injury severity, symptoms, mechanism of injury, time course of injury, as well as testing methods and paradigms. All these factors may influence the results of complex tasked-based functional studies (108).…”

Discriminating military and civilian traumatic brain injuries

“…According to several studies, differences do not exist between blast and non-blast-related TBI on measures of postconcussion symptom endorsement and various neuropsychological and cognitive measures (Cooper et al, 2012;Luethcke et al, 2011;Neipert et al, 2014;Norris et al, 2014). Differences between blast and non-blast-related TBI have been demonstrated, however, on measures of white matter integrity (Taber et al, 2014) and neural activation during response inhibition (Fischer et al, 2014) using magnetic resonance imaging. Neuroimaging measures may be more sensitive than behavioral measures for revealing potential group differences due to their ability to detect small alterations in brain tissue.…”

Prospectively Assessed Clinical Outcomes in Concussive Blast vs Nonblast Traumatic Brain Injury Among Evacuated US Military Personnel

“…17,18 Findings from previous investigations comparing patients with blast vs nonblast TBI vary. Specifically, similarities have been observed in neurocognitive performance, 14,19,20 symptom complaints, 6,20 and mental health, 5,20 while other investigations have found individuals with blast TBI to be worse compared with individuals with nonblast TBI in all 3 of these domains 13 or solely in mental health.…”