Source: Definition of Mild Traumatic Brain Injury Developed by the Mild Traumatic Brain Injury Committee of the Head Injury Interdisciplinary Special Interest Group of the American Congress of Rehabilitation Medicine.

J Head Trauma Rehabil 1993:8(3):86-87

Attorney Gordon S. Johnson, Jr.

One of the truly important minds in brain injury research is Dorothy Gronwall, Ph.D., a neuropsychologist from New Zealand. Beginning in 1974, Dr. Gronwall and her colleague, neurosurgeon Philip Wrightson, began devising ways to differentiate the attentional problems that those with subtle brain injuries had from uninjured controls. Remarkably, through this research into attentional problems, Dr. Gronwall predicted the direction this generation of microscopic neuropathology would take us in understanding the concussed mind.

In research now more than 20 years old, Dr. Gronwall and her colleagues established that even with young males, who had seemingly made full recoveries from concussion, that if their brains were put under sufficient stress, that they would do significantly worse than uninjured control groups. This research involved administering a test called the the Paced Auditory Serial Addition Task (the"PASAT") to a group of concussed college students. While the concussed students did worse than the controls shortly after their injuries, there scores on the PASAT duplicated that of the control group at thirty days. What this would have indicated to most researchers was that concussion did not cause permanent injury. But Dr. Gronwall and her colleagues added one additional factor into their study, replicating these same tests, on both the injured group and the controls under hypoxic (shortage of oxygen) conditions, the equivalent of being at 12,500 feet above sea level. Two years after their injuries, and apparent full recovery, the injured group did materially worse than the controls. (See Ewing R, McCarthy D, Gronwall D, Wrightson, P, "Persisting Effects of minor head injury observable during hypoxic stress." J. Clin. Neuropsychol 2:147-155, 1980.)

This discovery allowed Dr. Gronwall and her colleagues to conclude that even with otherwise healthy young people, apparent full recovery from concussion was incomplete and could be measured when sufficient stress was put upon the brain. She furthered concluded that this accounted for the reason that those in professions putting a premium on information processing and those over 40, would likely have the most significant deficits from seemingly mild injuries. (See her chapter in Levin, Mild Head Injury ©1989, Oxford. Note the year and author are different than the current book Mild Head Injury discussed below.)

In the generation since these studies were published, we have learned much about neuropathology which allows for this basic explanation of those with persisting deficits:

Concussion results in organic injury to the brain, in most cases, by the mechanism of diffuse axonal injury. This injury is more likely as a result of strain to axons than actual tearing, which over a period of 12-72 hours results in a cascade of events which can disrupt a significant number of neural connections, either because of the death or damage to the axons which connect the neuron bodies. Our current research into neuropathology indicates that significant regeneration of these neural connections can occur, but the extent of such regeneration falls off considerably with age and that regenerated neural connections are less efficient than premorbid. For this reason, individuals in professions which place a high demand on processing speed are more likely to experience deficits than others, and that most people who have suffered more than a Grade I concussion, will have some measurable deficits, if sufficient demands are made upon their brains.

In a sort of perfect symmetry, Oxford University Press has just published an authoritative yet beautifully written book, Mild Head Injury, wherein Dr. Gronwall and Dr. Wrightson provide the most current treatment and easily understood treatment of brain injury I have read. The irony is that this most current piece, incorporating all that we have learned in the generation since the PASAT study of 1974, says much of the same things that Drs. Gronwall and Wrightson have been telling us all along. What we get in addition in Mild Head Injury is the pearls of wisdom of 25 more years of enlightened clinical experience with subtlely injured minds - 25 years of enlightened clinical research from minds that that were a generation ahead when they started.

Next: Fatigue

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subtlebraininjury.com is a website with a mission to educate with respect to the magnitude of brain injury which does not involve coma - injuries that have been labeled by names which grossly minimize their potential impact upon the life of the injured person. This site is brought to you by the advocates of the Brain Injury Law Group, a community of plaintiff's trial lawyers across the United States united by a common interest in serving the rights of persons with traumatic brain injuries and a common commitment to fully understanding the anatomic, medical and psychological aspects of TBI

Additional Information

For a full treatment of the topic of brain injury, and recovering adequate compensation for those who have survived such injury, please visit our other pages. tbilaw.com A general treatment of all types of brain injury, including severe brain injury and concussion, with a special focus on the legal aspects of recovering full and adequate compensation for such injuries. tbilaw.com has been at the cornerstone of the web advocacy of the Brain Injury Law Group since it went online in 1996. waiting.com A page designed to assist those with issues regarding coma, especially in the acute phase when the doctors are saying "I just don't know." vestibulardisorder.com Addressing vertigo and dizziness resulting from trauma as well as information and resources for vestibular disorders.

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