What Happens in Brain Injury?
What happens to the brain at the point of injury?
Traumatic brain injury (TBI) refers to damage or destruction of brain tissue due to a blow to the head, resulting from an assault, a car crash, a gunshot wound, a fall, or the like.
In closed head injury, damage occurs because the person receives a blow to the head that whips the head forward and back or from side to side (as in a car crash), causing the brain to collide at high velocity with the bony skull in which it is housed. This jarring bruises brain tissue and tears blood vessels, particularly where the inside surface of the skull is rough and uneven; damage occurs at (and sometimes opposite) the point of impact. Thus, specific areas of the brain — most often the frontal and temporal lobes — are damaged. This focal damage sometimes can be detected through MRI and CT scans.
In closed head injury, the rapid movement of the brain can also stretch and injure neuronal axons — the long threadlike arms of nerve cells in the brain that link cells to one another, that link various parts of the brain to each other and that link the brain to the rest of the body. This widespread axonal injury interrupts functional communication within and between various brain regions and sometimes between the brain and other body parts. However, this type of diffuse damage typically cannot be detected through most currently available imaging technology, but can be detected using very sophisticated new techniques.
In sum, after a closed head injury, damage can occur both in specific brain areas (due to bruising and bleeding) and also be found throughout the brain (due to stretched or destroyed axons). The results of a closed head injury tend to affect broad areas of the individual's functioning, primarily due to the diffuse axonal injury. The extent of damage is correlated with the force of the blow to the head; for example, a head forced into a car windshield at high speed will tend to sustain more tissue damage than when the car is traveling at a slower speed.
Open head injury, the second type of TBI, occurs when the skull is penetrated, for example by a bullet. Damage following open head injuries tends to be focal, not diffuse, and the implications for subsequent impairment tend, also, to be focal and limited. However, such injuries can be as severe as closed head injuries, depending on the destructive path of the bullet or other invasive object within the brain.
What happens immediately after TBI?
Immediately following TBI, two types of effects are seen. First, brain tissue reacts to trauma and to tissue damage with a series of biochemical and other physiological responses. Substances that once were safely housed within the cells now flood the brain. These processes further damage and destroy brain cells, in what is called secondary cell death.
The second type of effect is seen in the individual's functioning. For those with more severe injuries, loss of consciousness (LOC) occurs at the time of trauma, lasting from a few minutes or hours to several weeks or even months. Lengthy LOC is referred to as coma. In such serious injuries, the first few days after trauma may also produce negative changes in respiration (breathing) and motor functions.
As an individual regains consciousness (those with the severest injuries may never do so), a variety of neurologically based symptoms may occur: irritability, aggression and other problems. Post-traumatic amnesia (PTA) is also typically experienced when an injured person regains consciousness. PTA refers to the period when the individual feels a sense of confusion and disorientation — Where am I? What happened? — and an inability to remember recent events.
As time passes, these responses typically subside, and the brain and other body systems again approach physiological stability. But, unlike tissues such as bone or muscle, the neurons in the brain do not mend themselves. New nerves do not grow in ways that lead to full recovery. Certain areas of the brain remain damaged, and the functions that were controlled by those areas may emerge as challenges in the individual's life.
Before discussing in greater detail what happens to the person after injury, which depends to great extent on the severity of injury, "severity" needs to be defined (in the next question).
What is meant by "severity of injury?"
Typically, "severity of injury" refers to the degree of brain tissue damage. Although the degree of such damage cannot be directly measured, it is estimated typically by measuring the duration of loss of consciousness (LOC) and the depth of coma (and sometimes by the length of PTA).
The scale most commonly used to measure the depth of coma is the Glasgow Coma Scale (GCS). The GCS is used to rate three aspects of functioning: eye opening, motor response, and verbal response. Individuals in deep coma score very low on all these aspects of functioning, while those less severely injured or recovering from coma score higher.
A GCS score of 3 indicates the deepest level of coma, describing a person who is totally unresponsive. A score of 9 or more indicates that the person is no longer in coma, but is not fully alert. The highest score (15) refers to a person who is fully conscious.
Severity of injury is typically categorized into three levels: mild (or minor), moderate and severe. A commonly used rule of thumb is that mild injury refers to LOC of less than 20 minutes and an initial GCS of 13-15. Typically, an initial GCS of 9-12 defines a moderate injury and 3-8 a severe injury.
Although initial "severity" measures may generally predict long-term impairment, initial severity scores do not necessarily correlate well with negative consequences in a person's life. The effects of TBI on individuals and the meaning of those effects depend upon a wide variety of factors, only one of which is initial "severity of injury."
How long does recovery take?
Recovery after injury is usually quite different for those with moderate-to-severe injuries versus those with mild injuries. And, as must be constantly kept in mind, recovery varies greatly from person to person. Thus, recovery will not be the same for any two people with TBI.
In mild TBI, one person may recover quickly and completely, while another may experience significant challenges even several years after injury. (Recovery after mild TBI is discussed more fully in a later question, What Problems Emerge after a Mild TBI?)
In more severe injuries, recovery is a multistage process, which typically continues in a variety of ways for months and years. However, the length of this recovery process is not uniform, and the stages of recovery that are typical when considering the population as a whole, may be very different for any specific individual. Stages may not proceed step-wise but may overlap, one stage with the next, or one or more stages may be skipped altogether. The early recovery process is discussed more fully in the next question.
How is recovery measured right after injury?
The progress seen during the immediate recovery period in individuals with severe to moderate TBI is often tracked using the Rancho Los Amigos Scale, which specifies eight levels — from the depths of coma to return to awareness and purposeful activity. These levels of recovery of functioning reflect processes within the brain, as it heals, stabilizes, and reorganizes itself to some extent.
Although the Rancho scale assumes that recovery will pass through eight stages, a small percentage of people with severe injuries remain stuck at Levels I to III for months or years. They remain in coma or in a relatively unresponsive state and fail to return to purposeful, appropriate functioning.
Rancho Los Amigos Scale
- Level I (No Response): The individual is in deep coma and does not respond to any stimuli.
- Level II (Generalized Response): The person sleeps most of the time, with periods of brief wakefulness. Responses and movements are largely reflexes not purposeful.
- Level III (Localized Response): The person is alert for lengthier periods. He/she reacts inconsistently to commands, but his/her responses are related to the type of stimulus presented. For example, noises will produce a listening response.
- Level IV (Confused and Agitated): As awareness increases, the individual's behavior reflects his/her sense of confusion and disorganization. Aggressive and/or silly behavior may be seen, with verbal abuse, agitated actions, and incoherent speech. The person's attention span is too short to allow full cooperation in treatment programs; and the person is unable to do basic tasks, such as eating, independently.
- Level V (Confused, Inappropriate, Not Agitated): Simple commands are now followed consistently; the person's long-term memory is returning; and she/he can now carry out over-learned skills such as eating. Difficulty is evident in following complex commands, short-term memory, learning new skills, and concentrating for more than a few minutes.
- Level VI (Confused, Appropriate): The individual begins to show goal-directed behavior, but usually still needs direction. The person is more aware of his/her deficits, family members, and so forth. He/she can carry out more tasks independently and retains relearned skills from one occasion to the next.
- Level VII (Automatic, Appropriate): The individual performs daily routines automatically and is better able to learn new skills, although slower than before injury. The person still has poor short-term memory; judgment and problem solving are still impaired.
- Level VIII (Purposeful, Appropriate): The person is able to function once more in the community. Impairments in cognitive, social, and emotional functioning, to a greater or lesser extent, may continue.