Until recently, microglia were thought to be helpful but unimportant "housekeeper" cells in the brain, but they connect our physical and mental health in surprising ways. When triggered—by chronic stressors, trauma, and viral infections—they contribute to depression and Alzheimer's. Under the right circumstances, however, microglia can be coaxed back into being healers, and as Donna Jackson Nakazawa explains here, microglia may be able to make brain repairs in ways that help alleviate symptoms and potentially prevent some diseases.