EFFECTS ON THE BRAIN  [ back to Brain Injury 101 ]
The brain is "the fragile dwelling place of the soul." When the brain becomes injured by trauma, we expect to see, and do see, changes in how the person perceives, remembers, thinks, feels and relates to others. Injury to the brain changes the functioning of the individual and his identity. This should not be surprising, since the brain is so highly vulnerable to injury from trauma. It is a three pound mass of jelly-like consistency made up of one hundred  billion neurons and their interconnections. It is 90% water, and cannot be expected to retain its integrity in response to traumatic events such as car crashes, falls or criminal assaults in which the head is battered.

How rapidly and how completely a person recovers from brain injury, depends on a variety of factors including severity of initial injury, age, pre-morbid education, personality and temperament, presence or absence of complications such as chronic pain and/or post traumatic stress disorder, quality of treatment, quality of social support network, and many others. Every person has a different brain, so it is not surprising that 100 people will respond in 100 different ways to a head trauma of similar force, direction and impact point on their skulls. Our brains vary anatomically on account of genetics, age and gender. The unique developmental, educational, psychological, nutritional, toxic exposure and trauma history of each persons' brain affects how his brain is wired and how well or poorly it can adapt to a particular traumatic event. Over the past few years, Dr. Paul Thompson, a neurologist at the UCLA Lab of Neuroimaging, has been creating a whole brain 3D atlas of the brains of 1000s of "normal" individuals and individuals with Alzheimer's Disease to help us better visualize the subtle differences. A by-product of this research is visual confirmation that every person's brain has a unique pattern of functional organization. This correlates with neurosurgery on epileptic and cancer patients in which mapping of the brain functions in an awake patient with an electric disrupter tool, shows the same unique layout of functions. In concrete terms, this means if you strike 100 people with a blunt instrument above and slightly behind the left ear with the same tool at the same level of force, you will be damaging different  brain circuits and disrupting different brain functions in each person, and each will respond differently. This is important, because in litigation the defense medical expert will often distort the truth by saying "most people struck in that part of the head show a different outcome than the plaintiff; therefore the plaintiff is faking his symptoms or they are the result of psychological stress not organic brain damage."

The brain circuits which get disrupted by trauma are composed of inter-connected neurons or brain cells. Neurons are nerve cells constructed to do the specialized work of the central nervous system. They consist of a cell body with a nucleus and cellular processes for the reception and transmission of nerve signals through chemical substances called "neurotransmitters". Each neuron has a large collection of fernlike dendrites for message reception and one large tubular axon for signaling other neurons. Each dendrite has spines with pores called receptor sites. Molecules of neurotransmitter are released from pre-synaptic vesicles at the tip of the axon and flow across the gap between nerve cells (the synapse) where they "bind" with receptors on nearby dendrites. This signals the receiving cell to open up its pores and allow ion exchange with the extra-cellular environment. When this process works as designed, the influx of ions triggers a "depolarization" of the receiving nerve cell, which sends a mild electric current (or "action potential") pulsing down its axon, and triggering axonal release of more neurotransmitter. The human brain sends messages at 1/10,000th of a second largely because its axons are coated with a natural insulation material known as myelin.

Trauma disrupts the normal process of communication between nerve cells by mechanical shaking and perturbation of cell membranes, mechanical striping away of myelin from axons, stretching of axons which triggers obstructive swellings to form in the axon and by triggering massive dumping of 1000s of time the normal quantities of neurotransmitters like glutamate. All these processes are destructive. Excess release of glutamate can cause nerve cells to literally explode. This happens when glutamate jams open nearby receptor sites and allows a toxic influx of calcium into nerve cells, shutting down their mitochondria, and depriving them of energy to work the sodium pumps to force sodium back out of the cell, resulting in extracellular water pouring in and bursting the cell like a balloon. 

When synapses are damaged and malfunction as a result of trauma, communication inside the brain is disturbed with evident consequences such as slowed thinking, forgetting of intentions or difficulty finding the right words to express oneself. Typically this occurs when external force on the head causes the brain to twist and bounce back and forth inside the hard, unyielding skull case. Although surface contusions to the gray matter may result, more often the damage is done by internal stretching and straining of the long axons, a form of microscopic damage not visible on MRI. Although a concussion causes an immediate episode of dazing or confusion (which may last just seconds or minutes), it generally takes 48 hours after the traumatic event for stretched axons to form obstructive swellings which block the flow of nutrients and gradually kill off the nerve cell or decrease its connections with other neurons that are no longer in physical communication.  A randomized kill off of   synaptic connections is much like a Florida hurricane ripping down phone lines in a helter-skelter manner. While the phone system as a whole is intact, some messages don't get through, others get delayed because of re-routing and others arrive in garbled fashion.

A person who suffers a concussion from closed head trauma will experience a momentary episode of dazing or confusion from twisting of the brain stem or an extra heavy discharge of neurotransmitters. This often clears by the time she is brought to the emergency room. Diffuse strain injury to axons produces no visible bleeding so the CT scan will be negative. Even if a CT scan could pick up microscopic damage to axons, it would not be visible in the ER right after the concussion, because the process of axonal destruction takes a good 48 hours to get going.   Thus an emergency room CT Scan will pick up bleeding in the brain from a depressed skull fracture, but cannot detect the damage done by mild brain injury because it has not happened yet. Due to poor training, many emergency room doctors equate a negative CT scan with complete absence of injury to the brain.

A great many victims of mild traumatic brain injury know intuitively that they are "different" following their accident, and that something is wrong with them, but never get properly diagnosed, treated, counseled, helped or rehabilitated. This happens so frequently because microscopic damage to axons is not detectible on standard neuroimaging techniques and does not produce any gross disturbances of reflexes (e.g. pupillary reflexes) that a neurologist would perceive as a significant abnormality of the central nervous system. Although PET scans can detect tiny disturbances of brain function, these tests are very expensive, and most insurers refuse to pay for them on the grounds of lack of "medical necessity." Fortunately many persons who suffer from the "milder" form of TBI (with no loss or only a minimal loss of consciousness and negative CT/MRI) eventually improve on their own, especially if they take time off work and get plenty of rest. For the ones who get better spontaneously, most show good improvement within three months post-accident and most, about 85%,  are symptom free within six to twelve months post -accident.

However, a minority of mild head injury, about 15%, show symptoms on a long term, even permanent basis. Typically, there is a mix of organic and psychological factors interacting to perpetuate their impairments on a chronic basis. It is now believed that at least some of these individuals have the APOE-e4 gene for Alzheimer's Disease. It is also believed that other consequences of mild TBI may perpetuate symptoms, especially when untreated or undertreated. These include depression, anxiety disorder, panic disorder, post-traumatic stress disorder, substance abuse, pain disorder,  sleep disorder and Rx medication side effects. Undoubtedly, the amount, the intensity and the complexity of life demands on the injured person play a role. Someone who was retired and sedentary before the brain injury will not experience the same level of complaints as someone who was a mother of 3 children or a full time breadwinner working as an accountant, software designer, attorney, engineer, physician, architect or equally challenging position. Persons of middle age ask a lot of themselves and become the most frustrated when they cannot function and meet their own demands. They also suffer from decreased neuronal reserve, i.e. they have fewer living brain cells than they did when they were children.