In our last blog, we introduced the reader to the potentially disastrous combination of TBI and PTSD conditions in a combat survivor. But the problem in combat is not just the intersection of these two “co-morbidities”, but the likelihood that a third complicating factor- preexisting anxiety – will also be found in combat veterans.
As we outlined yesterday, the Limbic System is the part of the brain which regulates anxiety and memory. Just as the corpus callosum is the collection of axonal fibers that connects the two hemispheres of the brain, the uncinate fasciculous is the collection of axonal tracts that connect the principal memory and anxiety centers of the brain to the frontal lobes – the thinking and maturity parts of our brain.
See http://www.waiting.com/limbicsystem.html
The principal structures involved include the following;
Hippocampus. The brain’s save button is the hippocampus. It is the part of the brain most important to converting immediate memory to long term memory.
Amygdala. The brain’s anxiety center is the amygdala. It is the amygdala that protected us from predators in the pre-historic times. It triggers our startle reflex in modern times and is the principal culprit in anxiety disorders.
Frontal Lobes. The frontal lobes are where we learn to become adults, where all activity is initiated, decisions made, emotions modulated and judgment’s made. The orbital frontal part of the frontal lobe, on the underside, is essentially the conductor of the brain’s symphony, the part that tells the other instruments when to start and stop playing. The frontal lobes coordinate all activity.
Uncinate Fasciculous. Connecting the above critical structures is the uncinate fasciculous, the axonal tracts that run from one end of the lower brain structures to the underside of the frontal lobes.
A person with a pre-injury anxiety disorder is far more vulnerable to post concussional problems (PCS). In a person with an anxiety disorder, the amygdala is already overreacting to potential anxious moments. It runs “hot” so to speak. When, as a result of trauma, such as a blast, damage occurs to the hippocampus, frontal lobes and the uncinate fasciculous, the information that gets moved across this lower brain circuit gets garbled. When information between the limbic system and the frontal lobes gets garbled, anxiety can become panic, depression can become organic rather than just reactive and the person’s ability to modulate emotions and make decisions, seriously impaired. The combination of pathologies in these areas -coupled with inefficient communication between them – creates a synergistic pathology far more functionally impairing than any one of those impairments might have been alone.
As serious as this premorbid vulnerability is in a civilian, it is far more serious in a soldier. Think of it this way. The amygdala is there to get us to run, without stopping to think. Fortunately for peace time activities in the modern world, our socialization has taught us when not to panic. A civilian has few times when he or she needs to rely on the amygdala. There are few great predators, few brushes with real danger. Thus, our frontal lobes and other emotional centers have tamed our amygdala, in not so different of a way than we tame a pet.
Yet, the amygdala is needed for combat. To survive, a soldier must rely on his instincts and must put his mind into a hypervigilant state. One of the biggest problems that soldiers have reintegrating into civilian life is learning how to stop this hypervigilance. PTSD is primarily a disease where the traumatic emotional stress has so changed the amygdala that it never entirely goes back to its peace time role.
Thus even before a TBI, a combat veteran is likely to have a heightened anxiety. Without that anxiety- the hypervigilance – the soldier may not survive. Depending on the level of previous battle stresses, that anxiety may have elevated itself to PTSD levels prior to the TBI. Thus, the risk of emotional dysfunction is not only increased by the very battle in which the soldier is injured, but also by the pre-injury emotional state.
The irony of all of this is that this convergence of co-morbities is laid upon those we expect to be the toughest. “The Few, the Proud” are those at greatest risk of becoming the homeless, the disturbed, the arrested. Sadly, I can offer no solution other than peace.
