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

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

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

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

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

TimeSlips is a program based on the idea that storytelling can be therapeutic for people with dementia. Dick Blau/TimeSlips hide caption

itoggle caption Dick Blau/TimeSlips