I am often frustrated when people mistake mTBI and PTSD because they can be so different. Admittedly PTSD is the hardest thing I face from day to day, but that is because of mTBI. Anatomically speaking PTSD is the over stimulation or use of the Hypothalmic Pituitary Adrenal (HPA) Axis. There is no simple way to describe neurology, but I will do my best at explaining my experiences in relation to my limited understanding of brain anatomy. The HPA is a apart of the limbic system which is one of the oldest traits in the human body. Our dogs and horses are some of the best aids to PTSD because we share this structure even if our cortex functioning is very different. The HPA and limbic system creates a stress response by emitting the chemical cortisol (often called adrenaline) which gives you energy (anger), pulls the blood out of your extremities in preference to organs (you will simply feel tingling or numbness in your limbs), and activates a larger part of your brain making you hyperaware. Think of the golden hour a casualty has to get into surgery, and to get fresh blood and coagulants before they start to crash. That is the final aspect of the limbic system's response to stress: the crash that inevitably comes after your body works at such high levels. That feeling of extreme fatigue and the inability to sleep is a direct result of cortisol, and also why battle fatigue was one of the first terms for PTSD.
PTSD is the persistence of this complex stress response into non dangerous situations. This interplay works with the cortex because the limbic system will provide the stressors to your consciousness so that you can more quickly respond to similar situations in the future. The HPA cortex relationship is a two way loop that can be instinctually triggered, by the older limbic system or by the cortex's memory of previously stressful events. I can see the way that anatomy and social construction works together in my memory of soldiers saying that sooner or later we are going to jump when a car back fires just like all these other guys, already favoring the stress responses of previous groups of veterans through a learned behavior, as well as reflexive reactions to triggers common to the tactics of insurgents in Iraq and Afghanistan. I was blown up in a stairwell so I hyperventilate in stairwells to this day. The anatomy of stress, the events themselves and the way that others have responded socially all effect the way we experience danger as well as the way we choose to process our memory.
But this is a post about mTBI and PTSD. How does this matter?
mTBI is actually a lot less complicated neurological than PTSD, though the experience is incredibly complicated, the concussive nature of high explosives as well as hitting ones head generally damages the brain and most effects the frontal cortex. The brain's protective coating is damaged by concussion and the cortex gets slammed into your skull. This generally erodes your whole brain functioning, but has one set of symptoms that makes PTSD a lot harder to manage. Cortex injuries limit a person's impulse control, and when a person has been exposed to serious life or death situations they are more likely to have a cortex that always fires up the limbic system's response to any stressor. Hence why for me the graduate seminar table and public speaking will often trigger panic attacks. Also the anger I felt in battle is worse because my cortex is not as capable as it was prior to concussions or repeated exposures to explosions. Everything is worse because you have eroded impulse control and every part yourb rain as a system is not your own. Your body is literally not yours to control. The WWI and WWII crack ups were not solely PTSD, but also damage to the cortex from shelling, because as Jonathan Shay as observed, PTSD is actually useful in combat. You always want to fight or fly, but you fight better as a unit so your trained to stick to the plan, that is until blasts and concussions add to this mix and make it harder to control the stress impulse.
You crash because we are only designed to go that hard in brief instances: the golden hour. You become depressed because you are exceeding the capability of human anatomy, and because you are losing control of your impulses. Worse cortisol damages the conscious memory when it is overused and the center of your brain that is self aware is consistently damaged. Kurt Vonnegut referred to scouts, himself included, as people that were controlled by their spinal column, shared location with the limbic system, because he understood the human brain in a profoundly human and intellectual fashion, but when the cortex is damaged it is nearly impossible to stop this life or death impulsivity.
I can remember my first nightmare and flashback like it was yesterday. I had just shot an RPG gunner in Mosul, I had a flashback that day and a nightmare that night. I knew it was PTS and I didn't care, I managed it and was upfront with the Physician Assistant about it. It was war, of course it was going to be terrible, but it was important for me to continue to do my part. However, when I got a concussion I could no longer see what was going on as natural and I got way to stuck in my limbic system. Everything was extreme and everything remains life or death because no matter how smart I can make myself my cortex doesn't have the impulse control that I once had. I can know something, but not feel something, because the emotional stress response is more powerful than my ability to control that impulse. I perform amazing feats because I am running on an extreme and then I crash because I am going way to hard all the time. I know this, but it is almost impossible to control the powerful impulse. I just hope I never lose the ultimate battle to the natural and constant ups and downs that come with the OIF/OEF cocktail.