The last time we were on the trail of Alzheimer's Disease, which killed Ronald Reagan, my next-door neighbor, and doubtless several great friends of yours, we learned that its risk factors were just like those of heart disease, high cholesterol which causes plaque to form in the brain's blood vessels.

Now scientists at UC San Diego have found a precursor condition that's just as important. Before symptoms are even apparent, proteins start clogging the pathways of axons, the nerve cells whose connections and re-connections represent actual thought. (The axon above is from a Coventry, England pain clinic.)

Think of the axon as a wire whose connection is constantly moving. Its connection transmits content in the form of electrical impulses. It's the brain's ability to constantly connect and re-connect billions of axons that makes it more powerful than any computer ever made.

The protein build-ups cause this wire, in effect, to lose its conductivity, so signals can't get through as quickly, and mental function slows, at first almost imperceptibly. It was previously known that these signals were blocked by proteins only in late-stage Alzheimer's, but now we know this happens very early in the disease process.

What was thought to be the result of the disease, in other words, turns out to be its cause.