Inside the aging brain, a molecular contest between two opposing chemical forces determines whether proteins remain functional or collapse into the harmful clumps associated with neurodegeneration. Researchers from an international team have mapped this tug-of-war — oxidation accumulating with age on one side, hydrogen sulfide-driven persulfidation holding the line on the other — and found that when the balance tips, the consequences resemble the very diseases humanity most fears in its later years. The discovery, published in Nature Structural & Molecular Biology, carries a rare note of hope: