University of Florida researcher Jennifer Stamps administers the peanut butter sniff test to a volunteer. Jesse S. Jones/University of Florida hide caption

itoggle caption Jesse S. Jones/University of Florida

Hospital intensive care units save lives, but people there often suffer from delirium. Cal EMA / Flickr hide caption

itoggle caption Cal EMA / Flickr

Stressed out? Who isn't? Stress can cause physical changes in the brain that may be linked to Alzheimer's. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Anne Jones, 62, and Robin Jones, 73, at their home in Menlo Park, Calif. He took a test that revealed proteins typical of Alzheimer's disease. Ramin Rahimian for NPR hide caption

itoggle caption Ramin Rahimian for NPR

Depression is common among old people, affecting up to 25 percent. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Scientists hope a new genetically modified rat will help them find Alzheimer's drugs that work on humans. Ryumin Alexander/ITAR-TASS/Landov hide caption

itoggle caption Ryumin Alexander/ITAR-TASS/Landov

Social worker Nuria Casulleres shows a portrait of Audrey Hepburn to elderly men during a memory activity at the Cuidem La Memoria elderly home in Barcelona, Spain, last August. The home specializes in Alzheimer's patients. David Ramos/Getty Images hide caption

itoggle caption David Ramos/Getty Images

Scientists have found that bilingual seniors are better at skills that can fade with age than their monolingual peers. iStockphoto.com hide caption

itoggle caption iStockphoto.com

Brain scans using Amyvid dye to highlight beta-amyloid plaques in the brain. Clockwise from top left: a cognitively normal subject; an amyloid-positive patient with Alzheimer's disease; a patient with mild cognitive impairment who progressed to dementia during a study; and a patient with mild cognitive impairment. Slide courtesy of the journal Neurology hide caption

itoggle caption Slide courtesy of the journal Neurology

A PET scan of the brain of a person with Alzheimer's disease. U.S. National Institute on Aging/Wikimedia Commons hide caption

itoggle caption U.S. National Institute on Aging/Wikimedia Commons