Headlines often dismiss brain games as a Silicon Valley gimmick. This week’s data from the Alzheimer’s Association International Conference in London say otherwise: a specific cognitive speed-training game has been shown to cut dementia risk by 25%, and it now appears to alter beta-amyloid — the protein that clogs up Alzheimer’s brains — in men. In a small study of 53 U.S. adults aged 65 and older, those who trained 2–4 hours a week for 4.5 months showed a blood marker...