Now scientists at the University of Southern California have made a discovery that is spawning a new theory about Alzheimer's.
"It's a chemical that's generated normally in the human brain at low levels and maybe in the Alzheimer's brain is generated at much higher levels," explained Valter Longo, a geriatrician at the university.
The theory is that the damaging amyloid plaques stimulate the production of specialized microglial cells - which respond like a clean up crew and rush to the site of any kind of brain infection or inflammation.
But instead of helping, those cells appear to be doing harm by producing a toxic chemical which can kill brain cells in as little as a day.
What's more important, reports CBS News Medical Correspondent Elizabeth Kaledin, is that researchers believe they know how to overcome the toxin, meaning they've found not only something that's killing brain cells, but also the blueprints for a drug to stop it.
"By knowing the details we develop drugs that block specific toxicity," said Dr. Longo.
The research is in its earliest stages and has yet to be tested even in mice, leading experts in the Alzheimer's field to raise the red flag of caution.
"Scientifically its a very interesting, very exciting new finding but it's implications for developing treatments for Alzheimer's are questionable," cautioned Dr. Zaven Khachaturian, Senior Advisor to the Alzheimer's Association.
Drugs to treat Alzheimer's disease remain one of medicine's most elusive goals; a vaccine that once seemed so promising in animal studies caused bad reactions in humans and had to be scrapped. So new science in this frustrating field is often greeted warily, bringing as much chance of failure as success.