Research conducted by a team that included scientists from Johns Hopkins University and the Minnesota Medical School in 2005 identified a substance in the brain which they have identified as causing memory loss. The researchers, aware that people with Alzheimer’s suffer memory loss before they are formally diagnosed, hypothesized that there is a substance in the brain that causes memory impairment before nerve cells begin to die. To test this hypothesis, the researchers manipulated the genetic make-up of mice to develop memory loss in the same way as people with the early signs of memory loss. Using mice that showed early signs of memory loss and had no plaques or nerve cell loss in the brain, they discovered a form of the amyloid-beta protein that is distinct from plaques. They extracted and purified this newly found protein complex and injected it into healthy rats. The rats suffered cognitive impairment. This revealed that the amyloid-beta protein does, indeed, have a detrimental effect on memory.

This research also proves that unnatural accumulations of two naturally occurring proteins in the brain, amyloid-beta and tau, are not the causes of memory loss, as previously believed.

(B. Bower "Early stress in rats bites memory later on: inadequate care to young animals delivers delayed hit to the brain". Science News. Oct 22, 2005. FindArticles.com. 06 Nov. 2006).