A new study finds that veterans and active-duty service members with combat-related post-traumatic stress disorder (PTSD) and mild traumatic brain injury (mTBI) have larger amygdalas than those with combat-related mTBI only.
The amygdala, an almond-shaped section of tissue in the temporal region of the brain, is involved in processing emotions such as fear, anxiety and aggression. It is also believed to play a major role in triggering PTSD symptoms.
The findings are published online in the Journal of Head Trauma Rehabilitation.
For the study, 89 veterans and active-duty military personnel underwent magnetic resonance imaging (MRI). About a third of the participants had both PTSD and mTBI (concussion), and the rest formed the mild-TBI-only control group.
The study’s lead author, Dr. Mingxiong Huang, is a neuroimaging scientist at the Veterans Affairs (VA) San Diego Health Care System. He says the finding of a larger amygdala in veterans with combat-related PTSD and mTBI was a bit of a surprise.
“Some previous PTSD research showed declines in amygdala volume based on the assumption of a loss of size due to injuries,” said Huang, also a professor in the department of radiology at the University of California San Diego (UCSD).
“Our finding of increased amygdala volume seems to point to different mechanisms, such as an exposure to repetitive fear and stress.”
Such exposure, he adds, may lead to an abnormal growth of the neural networks within the amygdala, a development that has been reported in animal studies but hasn’t been fully investigated in human PTSD studies. More research involving people with non-combat PTSD are needed to generalize this finding to other types of PTSD, he notes.
“The amygdala is involved with processing threat perception and arousal and with linking emotion to experience in complex ways,” said coauthor Dr. Douglas Chang, physician and researcher at VA San Diego and professor of orthopedic surgery at UCSD.
“A larger amygdala volume may be a sign of hyperactivity with an enlarged neural network. But we don’t know whether this is an attempt by the brain to cope with PTSD or whether the growth and enlargement is causing symptoms, like an electrical storm.”
“The situation may also resemble scar tissue formation on skin. Is this an organized response by the body to heal itself, or is the scar tissue going haywire and forming a grossly disfigured area? Another possibility is that this study simply identified at-risk people for PTSD with a pre-existing condition: an enlarged amygdala.”
Combat-related PTSD and mTBI are significant health care concerns in veterans and service members. It’s not unusual for both conditions to occur in the same person, based on evidence from a cross section of studies. Some of the symptoms are similar, such as depression, anxiety, insomnia, fatigue, and changes in memory and concentration.
However, the effect of PTSD and mTBI on neural pathways in the brain, as well as the impact of the co-existence of the two, is still unclear.
The researchers warn that the findings were based on an observational study and therefore can’t prove a cause-and-effect relationship, only a correlation. They say the findings have several implications for research and treatment.
“To be able to see a structural difference between these two cohorts and in this stage of PTSD really points to something going on with the amygdala,” Chang said.
“Can we use this as a screening tool to identify people at risk? Maybe this is an adaptive response that we can monitor and use to track different kinds of mental health treatment approaches.”