Understanding Mild Traumatic Brain Injury (TBI)

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It’s easy to tell that someone has suffered a brain injury if there is a bullet hole in their head or a skull fracture—but the more common form of closed-head trauma or mild traumatic brain injury (TBI), sometimes called a concussion, is harder for most people to recognize.

In many ways, a penetrating head injury or cracked skull is easier for a doctor or patient to deal with. At least there is no question about whether or not there is an injury, and it’s easy to tell precisely where the injury is. Since doctors know which parts of the brain do what, if they know exactly where the damage is, they can tell the patient and their family what to expect. The kinds of injuries produced by closed-head traumas tend to be more diffuse and can only be identified with very sophisticated and expensive imaging techniques—and even then, not very well.

Unless there was enough bleeding under the skull to produce a subdural hematoma that required surgery to relieve the pressure on the brain, it can be difficult for a TBI patient to prove to an insurer or employer that their condition is real. A person with a mild TBI can typically walk around and talk normally and does not seem obviously disabled. So there is often a sneaking suspicion that the person claiming to suffer from a TBI is “faking it” or mooching off the system to get special benefits or accommodations that they don’t really deserve. TBI sufferers themselves may not even feel they are as deserving as others with “real” injuries. Compared to a fellow soldier who has lost both legs, a veteran struggling with mild TBI may feel that he/she has no right to complain.   

Mild traumatic brain injuries are basically caused by your brain banging into your skull. Your brain floats in a pool of cerebrospinal fluid (CSF), which completely surrounds it and separates it from your skull. (See Simply Gray Matters Guide: Chapter 4.) Since your brain does not have a seat belt, there’s nothing to keep it from flying forward into your skull if your head is moving rapidly and then suddenly comes to a stop. If your head is shaken violently, or if you fall and hit your head, your brain sloshes around, smashes into the hard surface of the skull, bounces back and then smashes into the other side of the skull. It continues to bang around this way until the system runs out of energy—much like a racket ball smashed as hard as you can, will bounce off the wall in front of you, then keep bouncing off walls until it comes to a rest. How much banging around your brain will do depends on how much force it experiences.

The CSF dampens down some of the movement, but if you get a really good whack on the head or stand too close to a blast wave, it won’t be enough to protect your brain. Brain tissue is soft and delicate and easily damaged. There’s a reason why your body invested in a skull and all that cushiony CSF to protect it. The repeated compression of your brain tissue crushes and tears its small blood vessels, resulting in the equivalent of bruises or small strokes. The damaged blood vessels are unable to deliver an adequate supply of oxygen and glucose to the neurons that really need it to live. The meninges, which surrounds the brain (see Simply Gray Matters Guide: Chapter 4), also typically becomes bruised and swollen during a TBI and it is the injury to the meninges that causes the nauseating headache that is often the only early symptom after a mild TBI.

The brain does not have any pain receptors, but the meninges does. Therefore, the severity of the headache is not a very reliable marker for the amount of brain damage, but only indicates the amount of meningeal bruising.  However, the headache itself is a good indication that your brain got banged around enough to bruise it. Someone who experiences a mild concussion may or may not lose consciousness. The individual may or may not experience a temporary partial or total loss of vision or hearing.  But, it’s a good bet that someone with a concussion will have a really bad headache within half an hour or so. Nausea and vomiting are also highly likely after a TBI. (The author can attest to this from personal experience.)   Please note that if you suspect you have had a TBI, you should not take aspirin for the headache.    Other over-the -counter pain remedies are fine, but, for some reason, taking aspirin after a concussion dramatically increases the risk of developing tinnitus (ringing in the ears) which may persist for years.

  Soldiers and civilians still get gunshot wounds to the head or skull fractures, but with better helmets for both soldiers and athletes, the less dramatic form of TBI has become the most common type of brain injury. Body armor has largely succeeded in protecting US soldiers from many other types of serious injuries, but it does not keep their brains from being rattled around in their skulls if they happen to be in the vicinity of an exploding IED. Mild traumatic brain injury has become the signature medical condition of America’s Iraq and Afghanistan war veterans. Unlike the loss of a limb, such wounds are not easily recognized.

If someone who experiences a mild TBI is otherwise in good health and he/she rests for two or three days after the TBI and avoids further injuries, his/her body can usually repair the damaged blood vessels quickly, restore proper blood flow to the damaged areas of the brain, and minimize neuronal loss. However, often people do not recognize the need for such “down time.” The football player wants to get back in the game. The soldier wants to stay with his/her squad. The construction worker does not want to lose out on the extra overtime. Because having a splitting headache makes it more difficult for the person to concentrate, someone with a TBI has an even greater risk of having a second injury. Someone with a TBI does not even need to experience another concussion to do additional damage. Simply stumbling or staggering around can jostle the brain enough to prevent the repair crews from being able to do their jobs properly. It would be like trying to put air in a car tire while someone is driving the car. With repeated injury or lack of proper repair conditions, some level of permanent brain damage is inevitable.

The symptoms of a TBI depend on things like the force of the impact or blast wave, the angle of momentum, the number of prior injuries, the individual’s health status at the time of the injury, and their genetics. Since none of these factors can usually be known with any degree of precision outside of a lab experiment, the outcome for any TBI patient can be hard to predict.  In infants, shaken baby syndrome can be fatal because the neck muscles are not strong enough to keep the brain stem (which controls breathing), from being banged around. In adults, closed-head traumas rarely have such dramatic consequences. The parts of the brain that control the most of your vital functions are better protected than the rest of the brain. They’re surrounded by a second set of CSF-filled sacs (the lateral ventricles), which act like shock-absorbing cushions (See: Simply Gray Matters Guide: Chapter 4 & 5).

The parts of your brain most likely to be damaged by a TBI are, not surprisingly, those closest to the surface, particularly those in the front of the brain: the cerebral cortex and particularly the prefrontal cortex (See Simply Gray Matters Guide: Chapter 5). The cerebral cortex is responsible for allowing you to perform the kinds of tasks that you are consciously aware of doing, and which we think of as making us who we are. It is not just involved in seeing and hearing, but more importantly in identifying what you see and hear and deciding what to do about it.  The prefrontal cortex is mostly involved in tasks that require putting together lots of different kinds of information in order to plan and coordinate complex sequences of activities to achieve a goal.

The kinds of symptoms caused by mild TBI tend to be problems with higher order information processing and planning. Because the amount brain damage arising from a mild TBI tends to be rather small, basic vision, hearing, or overall IQ are not likely to be affected. However, TBIs frequently affect specific brain functions that can create a lot of problems for patients.   Any part of the brain can be damaged by a TBI but a few functional areas seem to be more likely to be damaged, or at least to be damaged in ways that patients actively complain about.   Keep in mind that doctors only know about the symptoms that are reported to them, and changes that do not negatively impact the patient’s life are not likely to be mentioned.  There could be many TBI patients who experience a sudden change in their musical preferences, but they would not likely make an appointment with their neurologists about that.

The kinds of problems we do know about for TBI patients can be very difficult to handle. For example, the part of the brain that calibrates emotional responses to match actual circumstances seems to be frequently damaged. This part of the brain receives information from the emotional centers of the brain, as well as data from real-time analysis of the circumstances generating the emotional response. It puts these two kinds of information together to decide how angry, sad, happy, etc. you actually ought to be in your present situation and then helps you chose an appropriate response.  If this automatic emotional calibration mechanism fails to function properly, emotions may be experienced as being either totally on or totally off, with nothing in between. Normal anger becomes uncontrollable rage. Ordinary sadness is experienced as absolute despair. A previously easy-going person can become emotionally volatile after suffering from TBI.

Another part of the brain that appears to be frequently damaged by TBIs is the area that sequences multistep tasks. This part of the brain understands temporal relationships. It makes sure you always put on your socks before reaching for your shoes. Without this effortless putting of things together in the right order, jobs that require you to perform complex tasks can become all but impossible. You would constantly have to backtrack as you keep realizing that there was something else that you should have done first. An emergency medical technician may start to insert an I.V. line, only to have to stop because he realizes that he didn’t sterilize the area first. He knows better. He has put in I.V. lines thousands of times before, but now he has to consciously think about each little step of every task.

Another common complaint of TBI patients is a problem with concentration. Many TBI patients report having more trouble filtering out distractions. The effort to tune out extraneous sights, sounds, and smells can become very tiring.    

The specific functional problems resulting from a TBI are highly variable, but the most common complaint is frustration. Your doctors have given you a clean bill of health, but something is wrong and you just can’t put your finger on what it is. Things that used to be easy for you now suddenly require much more effort.

Since many of the symptoms of mild TBI are the same as those for post-traumatic stress disorder (PTSD) and people often do not go to a doctor for a mild concussion (and therefore the TBIs are not documented in their medical records), patients with mild TBI are often diagnosed as having PTSD. This is not terribly surprising since the circumstances that generate a lot of TBIs are the same ones that generate high levels of stress, i.e. combat situations or domestic violence. So there is a good chance that someone with a TBI also has a little PTSD.

In addition, the rules for qualifying someone as having a disability with PTSD are generally somewhat looser than those for TBI. The VA benefits administrators, for example, have now been instructed that they should just presume that any service member who did a couple of tours in Iraq has probably witnessed enough horrific events that any PTSD symptoms are likely service related. Physical injuries, however, still require documentation about where, when, and how the injury occurred, as well as supporting lab tests or treatment histories. If a service member’s problems could be due to TBI or PTSD, it is sometimes just easier to go with PTSD.

In many respects, the accuracy of the diagnosis does not matter very much. Both TBI and PTSD involve mild brain damage. In TBI, the damage is caused by physical forces damaging small blood vessels, in PTSD, the damage is caused by a chemical assault from stress hormones produced by your body in response to prolonged periods of high level stress.

The treatments for TBI and PTSD are also basically the same. Since doctors cannot go in and fix the software, they have to develop a software patch to work around the problem. Cognitive behavioral therapy and mental practice help your neurons to build new synapses and bulk up existing ones in the same way that physical exercise builds up muscles. There is no pill for this. You just have to push your brain to make new connections.

The good news is that there is a lot of redundancy and extra capacity in the nervous system, as well as a great deal of plasticity (see Simply Gray Matters Guide Section 3). So if you keep exercising the right synaptic pathways, other neurons can gradually take over the functions of the ones that were lost. They may not be able to do the job quite as well as the ones that they’re replacing, but your life can get an awful lot better.