Other research has shown that blows to the head in soccer can, over time, produce changes similar to those of CTE. The same is true for other head traumas, like head banging and repeated blows to the head from domestic abuse (more on this later). Although athletes appear, at least at the this point, to make up the majority of CTE patients, there's no reason that other types of recurrent head traumas would not pose similar risks.

WHAT'S HAPPENING IN THE BRAINS OF CTE PATIENTS

The brain changes accompanying all forms of dementia are still being worked out. Amyloid-beta plaques and the accumulation of tangled bundles of protein filaments (which include deposits of the protein, tau) are hallmarks of Alzheimer's disease. Interestingly, amyloid-beta accumulation is not so widespread a phenomenon in CTE as it is in Alzheimer's. But, like Alzheimer's and other forms of dementia, CTE is marked by the accumulation of tau in certain regions of the brain. Researchers are still working to determine just why tau accumulates in the first place, and what can be done to stop it.

Autopsies of CTE patients' brains show a distribution of large and small band-shaped and small flame-shaped tangles of tau protein inside cells. These tau tangles can accumulate in the brain, similar to those seen in other dementias, but in CTE the shape of the tangles appears to be quite different from those in Alzheimer's. Tau accumulation is present in higher concentrations in certain areas of the brain in CTE, particularly around blood vessels.

About 30 percent of people show higher levels of amyloid-beta proteins after having head injuries. More research is needed to determine the fundamental neurological differences among the dementias.

WHY TRAUMA LEADS TO TAU (AND OTHER CHANGES)

When the head undergoes a trauma, the brain takes a hit. Brain tissue may be insulated by layers of bone and fluid, but severe or repeated injuries disrupt the neural communication in the brain. Recent research on the long-term effects of concussion offers a picture of the lasting effects a brain injury can have. Lateral, or side-to-side, traumas are more damaging than sagittal, or front-to-back, motion.

One theory is that during injury blood flow to the brain becomes disrupted, which leads to oxygen deprivation (ischemia). Some suggest this phenomenon could lead to too much tau being deposited in the brain. This concept is borne out in the distribution of tau, which is often found in the depths of its wrinkles. Alternatively, since tau accumulates near the blood vessels, it could be that the physical force from repeated blows to the head lead to damage to the vascular network of the brain, which could lead to the tangles seen in CTE.

The brain trauma associated with CTE may also trigger the death of neurons; inflammation in the brain; and damage to the white matter, the connective fibers in the brain by which neurons "talk" to one another. One team of CTE researchers suggests that there are probably many "pathological cascades" that are occurring over time. These cascades are thought to continue throughout the course of a lifetime. And the worse the initial injury -- or injuries -- the more severe the brain damage that can follow.