Trotter Benjamin B, Robinson Meghan E, Milberg William P, McGlinchey Regina E, Salat David H
1 VA Boston Healthcare System, Translational Research Center for Traumatic Brain Injury and Stress Disorders, RR&D TBI Center of Excellence, Boston, Massachusetts USA and Geriatric Research, Education, and Clinical Center, VA Boston Healthcare System, Boston, Massachusetts, USA 2 VA Boston Healthcare System Neuroimaging Research for Veterans Center, Boston, Massachusetts, USA.
1 VA Boston Healthcare System, Translational Research Center for Traumatic Brain Injury and Stress Disorders, RR&D TBI Center of Excellence, Boston, Massachusetts USA and Geriatric Research, Education, and Clinical Center, VA Boston Healthcare System, Boston, Massachusetts, USA 3 Harvard Medical School, Boston, Massachusetts, USA.
Brain. 2015 Aug;138(Pt 8):2278-92. doi: 10.1093/brain/awv139. Epub 2015 Jun 1.
Mild traumatic brain injury, or concussion, is associated with a range of neural changes including altered white matter structure. There is emerging evidence that blast exposure-one of the most pervasive causes of casualties in the recent overseas conflicts in Iraq and Afghanistan-is accompanied by a range of neurobiological events that may result in pathological changes to brain structure and function that occur independently of overt concussion symptoms. The potential effects of brain injury due to blast exposure are of great concern as a history of mild traumatic brain injury has been identified as a risk factor for age-associated neurodegenerative disease. The present study used diffusion tensor imaging to investigate whether military-associated blast exposure influences the association between age and white matter tissue structure integrity in a large sample of veterans of the recent conflicts (n = 190 blast-exposed; 59 without exposure) between the ages of 19 and 62 years. Tract-based spatial statistics revealed a significant blast exposure × age interaction on diffusion parameters with blast-exposed individuals exhibiting a more rapid cross-sectional age trajectory towards reduced tissue integrity. Both distinct and overlapping voxel clusters demonstrating the interaction were observed among the examined diffusion contrast measures (e.g. fractional anisotropy and radial diffusivity). The regions showing the effect on fractional anisotropy included voxels both within and beyond the boundaries of the regions exhibiting a significant negative association between fractional anisotropy and age in the entire cohort. The regional effect was sensitive to the degree of blast exposure, suggesting a 'dose-response' relationship between the number of blast exposures and white matter integrity. Additionally, there was an age-independent negative association between fractional anisotropy and years since most severe blast exposure in a subset of the blast-exposed group, suggesting a specific influence of time since exposure on tissue structure, and this effect was also independent of post-traumatic stress symptoms. Overall, these data suggest that blast exposure may negatively affect brain-ageing trajectories at the microstructural tissue level. Additional work examining longitudinal changes in brain tissue integrity in individuals exposed to military blast forces will be an important future direction to the initial findings presented here.
轻度创伤性脑损伤，即脑震荡，与一系列神经变化有关，包括白质结构改变。新出现的证据表明，爆炸暴露——伊拉克和阿富汗近期海外冲突中最普遍的伤亡原因之一——伴随着一系列神经生物学事件，这些事件可能导致大脑结构和功能的病理变化，且这些变化独立于明显的脑震荡症状而发生。由于轻度创伤性脑损伤史已被确定为与年龄相关的神经退行性疾病的一个风险因素，爆炸暴露导致脑损伤的潜在影响备受关注。本研究使用扩散张量成像来调查在19至62岁的近期冲突退伍军人的大样本中（190名有爆炸暴露者；59名无暴露者），与军事相关的爆炸暴露是否会影响年龄与白质组织结构完整性之间的关联。基于体素的空间统计学显示，在扩散参数上存在显著的爆炸暴露×年龄交互作用，有爆炸暴露的个体表现出朝着组织完整性降低的更快速的横断面年龄轨迹。在所检查的扩散对比测量指标（如分数各向异性和径向扩散率）中，观察到了显示该交互作用的不同且重叠的体素簇。显示对分数各向异性有影响的区域包括在整个队列中分数各向异性与年龄呈显著负相关的区域边界内外的体素。区域效应对爆炸暴露程度敏感，表明爆炸暴露次数与白质完整性之间存在“剂量反应”关系。此外，在有爆炸暴露组的一个子集中，分数各向异性与自最严重爆炸暴露以来的年数之间存在与年龄无关的负相关，表明暴露后时间对组织结构有特定影响，且这种影响也独立于创伤后应激症状。总体而言，这些数据表明爆炸暴露可能在微观结构组织水平上对脑老化轨迹产生负面影响。进一步研究暴露于军事爆炸力的个体脑组织完整性的纵向变化将是未来一个重要的研究方向，以拓展此处呈现的初步研究结果。
