Severe and moderate traumatic brain injury, by definition, are immediately accompanied by a significant period of LOC (loss of consciousness) and PTA (post-traumatic amnesia). They do produce visible areas of damage on CT and MRI. Severe TBI (and to a lesser extent moderate TBI) may also be accompanied by temporary or permanent disorders of vision, speech, swallowing, movement and balance, which are so obvious as to be readily apparent to the untrained observer. Mild brain injury is distinctly different. It frequently occurs with no detectible loss of consciousness, and otherwise with just a brief period of LOC never exceeding 20 minutes.

Mild TBI is marked at the accident scene by an episode of dazing or mental confusion with brief interruption of continuous memory, however slight. While severe and moderate TBI always result in admission to a hospital, at least half of all persons with mild TBI are not even brought to an emergency room. The National Institutes of Health concluded in a report published 9/8/99 in the New England Journal of Medicine that many cases of mild TBI go undiagnosed and untreated.

Mild brain injury and PCS (Post-concussion syndrome) share all of the following symptoms, which manifest themselves more or less completely and more or less intensely in different patients following closed head trauma: headache, floaters, hyper-sensitivity to light and/or noise, lightheadedness, dizziness, blurry or dimmed vision, double vision, nausea, vomiting, poor short term memory, insomnia, fatigue, apathy, decreased libido, social withdrawal, irritability, sudden outbursts of anger and profanity, emotional lability, slowed thinking, having to re-read material over and over, inability to execute routine task sequences on automatic pilot, inability to learn new facts, disorganization, loss of ability to manage one’s paperwork and appointments, diminished attention span with easy distractibility and inability to maintain divided attention to two or more stimuli and a host of other symptoms. Are mild TBI and PCS the same thing? Some physicians say yes and others no.

Because most if not all these symptoms are consistent with a variety of disorders, it is critical to go through differential diagnosis utilizing neuro-imaging; neuropsychological testing of post-morbid functioning; careful estimation of pre-morbid functioning in the cognitive, emotional, behavioral, social and vocational areas; careful review of the type and amount of head trauma with attention to degree and duration of alteration of mental status; post-accident neuropsychological testing; and assessment of post-accident functioning from interviews with SOs (significant others, such as the injured person’s spouse, parents, children, family doctor, employer and friends). If the review of these factors indicates the most likely explanation for the problems is mild TBI, then it is perfectly safe and correct for that patient to treat mild TBI and PCS as equivalent terms.

The brain is unimodal and heteromodal. Unimodal means it has columns or clusters of cells which perform a specific task in isolation from other areas, such as olfactory cells which only identify smells or cells in the primary visual cortex which only identify the edges, colors or textures of objects. This is also called parallel processing. Heteromodal means integrated activity of different brain areas, for example identifying a friend’s face links simultaneous processing by the frontal lobes where the data is attended to and stored briefly while activating “face recognition” cells in the temporal lobe, the seat of that type of memory file; the parietal lobe (locating the face in a spatial context), the occipital lobe (processing the appearance of the face), limbic areas such as the amygdala which imbue recognition of the face with emotions, and so forth. If one type of circuit is damaged for integrated processing, then odd results occur, such as being able to see a face, but not recognize it and put a name on it, or being able to recognize who the face belongs to without being able to access any feelings about that person. Much of what we know about correlative neuro-anatomy comes from seeing what people can no longer do after a certain identified portion of their brain has been damaged. We also learn what the brain can still do without the missing part. This is where neuropsychological testing comes in.

When a person complains of “poor memory” after a TBI, we cannot know which aspect of his memory is poor, and whether the poor quality relates to the TBI (rather than something else, say age), without testing. It is the testing which lets us know how poor the person’s memory is vs. age matched controls without TBI, and which aspect of the memory is poor – verbal, visual, auditory, and whether the area of the brain displaying decreased function was likely exposed to the trauma. etc.

Researchers using PET and fMRI have begun to localize many brain functions to specific areas. When solving problems with a verbal strategy people tend to use Broca’s area in the left postero-lateral frontal lobe, and when solving spatial problems with a visual strategy they tend to use the right superior parietal area, as was imaged with fMRI by a research team at Carnegie Mellon which just published its findings in the June 2000 issue of Cognitive Psychology. In the July 21, 200 issue of Science Dr. John Duncan and colleagues of the Medical Research Council in Cambridge, England, reported that the left dorso-lateral frontal lobe was activated by taking traditional IQ tests, and they dubbed that area the brain’s “master problem solver” and the “seat of central intelligence for organizing and coordinating information from other parts of the brain.” Whether this lofty claim is borne out, or not, it does point up that the brain has junction sites where different information streams come together. While massive trauma to both hemispheres of the brain is likely to cause a permanent vegetative state, most brain injuries cause partial damage, leaving some functions impaired and other spared.

The functional outcome is not just a result of which areas were damaged, but how well the victim can compensate or make up for lost function by drawing upon spared areas of his brain and using them in adaptive ways. This is where neuropsychological assessment and TBI rehabilitation come together. The treatment team wants to know not only post-incident weaknesses in function, but pre-incident strengths and skills which can be called upon during recovery.

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