Washington ? Doctors can’t tell if Leif Utoft Bollesen’s mild memory loss will remain an annoyance or worsen, but experimental checks of the Minnesota man’s aging brain may offer clues.

About 1 million people a year begin a mental slide called mild cognitive impairment, or MCI, with forgetfulness that’s somewhere between healthy aging and Alzheimer’s disease. Now this gray zone is undergoing an evolution, with growing study of techniques to help predict which MCI patients may be on a path to later dementia — and who shouldn’t worry.

Many doctors aren’t waiting. A study published in the journal Neurology last week found 70 percent of neurologists say they prescribe Alzheimer’s medications to at least some of their MCI patients, hoping the drugs will slow their decline. That’s a startling number considering there’s no proof yet the drugs can do that even if doctors knew who’s most at risk.

Still, it’s becoming more and more clear that Alzheimer’s starts ravaging the brain at least a decade before memory problems appear. Thus stalling it may require treating the earliest symptoms, just as preventing a stroke begins with treating high blood pressure.

But to discover an early-stage therapy requires first discovering whose MCI really is pre-Alzheimer’s.

So when the National Institute on Aging and the nonprofit Alzheimer’s Association proposed new guidelines for diagnosing both full-blown Alzheimer’s dementia and that confusing MCI, they went an extra step. The draft also offers a roadmap for researchers testing new technology to help separate out the different types of MCI.

On the list: experimental PET scans that check for abnormal brain buildup of an Alzheimer’s-linked gunk called beta-amyloid. Bollesen, 78, is getting that and other brain scans at the Mayo Clinic in a large study hunting for patterns that predict progression.