Any kind of severe brain injury increases the risk of developing dementia later in life. Starting with this hypothesis, researchers from Washington University School of Medicine in St. Louis and from the University of Milan sought to find out why brain injury is linked to a higher risk of developing Alzheimer's disease. The study is to be published in the August 29 issue of Science.

Researchers took samples of the fluid between the brain cells of 18 patients who were recovering from traumatic brain injuries or ruptured brain aneurysms for this study.

Changes in the amount of amyloid beta, a protein that is believed to play a key role in Alzheimer's disease, were thoroughly studied.

"Proving that we can directly measure amyloid beta in the human brain is an important step forward for both clinical and basic research, and that may be true not just in Alzheimer's disease but also in other serious neurological disorders," says co-first author David L. Brody, M.D., Ph.D., a Washington University neurologist.

Apparently, as neuronal activity increases, levels of amyloid-beta in the brain also go up. This protein is best known for causing plaques in the brains of people with Alzheimer’s disease. It is a normal component of the brain, but scientists do not really know what it does.

Similar previous studies were made using mice instead of men and they showed that amyloid-beta is a byproduct of brain cell activity, and with studies in people that show the areas of the brain that are most active are the most prone to developing Alzheimer’s plaques.

Nothing is known for sure yet. “This study raises more questions than it answers,” Brody says. “It’s really just the beginning.”