Blasts to the Head ‘Primed’ Brains for PTSD, Study Says

Photo: U.S. Air Force

The “signature wounds” of the wars in Iraq and Afghanistan — post-traumatic stress disorder and traumatic brain injury — are both rooted in traumatic events. Until recently, though, military docs mostly treated them as two different health problems: one physical, the other psychological. That approach might be poised to change, thanks to a new study, which shows that injuries to a specific part of the brain “primed” it for PTSD’s psychological ailments.

Post-traumatic stress disorder is widely known as the psychological condition that’s followed soldiers home from Iraq and Afghanistan. The connection between war and PTSD is simple enough: Soldiers undergo a traumatic experience, if not several, overseas. Those traumas stay with them, and seem to have a profound impact on their stress hormones and brain chemistry. The result? Symptoms like nightmares, paranoia and angry outbursts.

In comparison, traumatic brain injuries (TBIs) seem extremely different. These injuries are caused by a physical trauma — an IED attack, for example — that actually rattles the brain inside the skull. Subsequent brain damage can cause everything from vomiting and headaches to long-term loss of sensation and speech impediments.

Scientists have known for a while that TBIs and PTSD are connected. One 2008 study concluded that 44 percent of personnel with a TBI also suffered from PTSD, compared to 9 percent of those without physical injury. Of course, the link seems obvious: It follows that driving a Humvee that’s suddenly blown to pieces will rattle the skull and also trigger psychological distress.

But researchers now suspect that the link goes even further: They’ve concluded that the physical blow from a TBI changes a key part of the brain, making a soldier more at risk of developing PTSD in the future.

Scientists at the University of California at Los Angeles, led by Dr. Maxine Reger, this week published a study that uses rats to examine the relationship between TBI and PTSD.

They first divided the animal subjects into two groups. The researchers used physical force to cause TBIs among the rats in one group. Those in the other group were left unscathed.

Then the team waited two days before exposing the rats to fearful experiences. The point of waiting was to separate the physical trauma (the TBI) from the psychological. Researchers wanted to know whether, days later and during an entirely different experience, a TBI would have any impact on PTSD risk.

Lo and behold, rats in the TBI group did react differently to fearful stimulus. In fact, they exhibited “inappropriately strong fear,” according to Dr. Michael Fanselow, one of the researchers involved in the study. Rats with healthy noggins, however, exhibited more appropriate reactions.

“It was as if the injury primed the brain for learning to be afraid,” he said in a statement.

At the core of the finding is one brain region, called the amygdala. Scientists already know that this tiny bundle of neurons is extremely vulnerable to damage during a brain-rattling event that causes a TBI. The amygdala is also one of the most important brain areas where PTSD is concerned, because it regulates fear response.

After their experiments, the team analyzed brain tissue from the amygdala of several rats. Among rats afflicted with a TBI, the amygdala had significantly more receptors for neurotransmitters that are involved in the learning process. In other words, a TBI somehow causes these receptors to multiply, meaning that there are more of them available to be activated by neurotransmitters. So when a person is exposed to a scary event, their amygdala is, oddly enough, more capable of learning fear.

In a human context, the study’s findings (roughly) suggest the following: If two soldiers are exposed to the same psychologically scarring event, the soldier who suffered a TBI last month would be more likely to develop PTSD than his colleague.

Of course, it’s not that simple. Scientists already know that all sorts of other factors, from genetics to childhood environment, affect a soldier’s risk of developing PTSD. And even if TBIs are a risk factor, they aren’t the only one — not everyone who gets PTSD, whether soldier or civilian, also suffered a traumatic brain injury sometime in the past. Likewise, not all TBI sufferers eventually end up with PTSD.

That said, the study could break new ground in the Pentagon’s efforts to treat, diagnose and prevent PTSD and TBI. Thus far, the military hasn’t had much luck unraveling either one. Figuring out how and where the two illnesses are tangled together might be a good place to start.