WASHINGTON (AP) — A handful of Alzheimer's patients signed up for a bold experiment: They let scientists beam sound waves into the brain to temporarily jiggle an opening in its protective shield.

The so-called blood-brain barrier prevents germs and other damaging substances from leaching in through the bloodstream — but it can block drugs for Alzheimer's, brain tumors and other neurologic diseases, too.

Canadian researchers on Wednesday reported early hints that technology called focused ultrasound can safely poke holes in that barrier — holes that quickly sealed back up — a step toward one da...