The first evidence of a causal link between traumatic brain injury and an increased risk for post-traumatic stress disorder has been provided by scientists at the University of California, Los Angeles.
The study also suggests that individuals who experience even a mild traumatic brain injury face a higher risk for developing an anxiety disorder and should try to avoid stressful situations for at least awhile.
The motivation for the study (conducted in rats) was the observed association between traumatic brain injury (TBI) and PTSD, especially in military veterans, said Michael Fanselow, a UCLA professor of psychology and the senior author of the study.
The reasons for this link are unclear. Perhaps the events that cause brain injury are also very frightening and the correlation between TBI and PTSD is merely incidental. However, Fanselow and his colleagues hypothesized that the two “could be linked in a more mechanistic way.”
For the study, scientists separated the physical and emotional traumas by training the rats with “fear conditioning” two days after they experienced a concussive brain trauma — ensuring that the brain injury and fear occurred on separate days.
“We found that the rats with the earlier TBI acquired more fear than control rats (without TBI),” said Fanselow, a member of UCLA’s Brain Research Institute. “Something about the brain injury rendered them more susceptible to acquiring an inappropriately strong fear. It was as if the injury primed the brain for learning to be afraid.”
To investigate this further, the researchers analyzed the rats’ amygdala, which is the brain’s important center for fear learning.
“We found that there are significantly more receptors for excitatory neurotransmitters that promote learning,” said Maxine Reger, a UCLA graduate student of psychology in Fanselow’s laboratory and the lead author of the study.
Fanselow added, “This finding suggests that brain injury leaves the amygdala in a more excitable state that readies it for acquiring potent fear. One of UCLA’s great strengths is the spirit of collaboration that allows scientists from very different departments to combine their very different expertises to answer important but difficult questions.”
The study is published in the journal Biological Psychology.