Post-traumatic stress disorder (PTSD) and traumatic brain injury (TBI) are both devastating conditions linked with high disability and suicide rates. In the past, the two unique conditions were often confused because they share similar symptoms and often co-occur.
Dr. Jeffrey Spielberg and colleagues at the VA Boston Healthcare System say one area lacking in thorough research was regarding the exact brain networks disturbed in these disorders, which led them to examine these networks in veterans using functional magnetic resonance imaging and graph theory tools.
As the report published in Biological Psychiatry explains, graph theory is a sophisticated analysis that allows researchers to understand brain networks at a level of complexity that only became possible recently. This system allows for the examination of the patterns of brain connections, rather than focusing only on individual connections.
For the study, the researchers recruited 208 veterans of Operation Enduring Freedom, Operation Iraqi Freedom, and Operation New Dawn, all of whom had previously experienced a traumatic event. This led the researchers to discover veterans with more severe PTSD re-experiencing symptoms, such as flashbacks or reliving the event, showed weaker connectivity in two networks.
The first network altered in these individuals includes the hippocampus and prefrontal cortex. and plays a role in providing contextual information. This led the researchers to believe the hippocampus may be overgeneralizing trauma-related memories, which causes the brain to incorrectly classify non-threatening cues as “unsafe”.
The second network was found only in veterans who also experienced comorbid TBI, and includes the basal ganglia and prefrontal cortex. The network has been found to be involved in working memory.
The report concedes the research cannot identify with complete certainty if the observed brain network disturbances were present before the individuals suffered a traumatic event, because all veterans involved in the study had already experienced a traumatic event beforehand. The researchers say more study will be needed to hopefully clarify this factor.
“It may never be possible to fully distinguish the role of the severity of stress, the capacity for resilience to stress effects, and the presence of mild TBI in PTSD-related distress and disability because these factors are so complex and intimately entwined,” said Dr. John Krystal, Editor of Biological Psychiatry.
“However, this study suggests that there are subtle but important differences in brain circuit functional connectivity related to the impact of traumatic stress among individuals with and without TBI. These data provide additional evidence that TBI may complicate the capacity for recovery from traumatic stress-related symptoms.”