Pictured is the mouse hippocampus, a brain region containing cells that process memories. The green cells are active during a fearful experience, driving defensive responses and forming a physical representation of a fear memory. The red cells are involved in the recollection of the same memory, and thus cells fluorescing both green and red form a more stable representation of memory. Dorst et al. found that artificially reactivating these cells drives the behavioral expression of fear in a manner that depends on the animal’s physical surroundings. For more information, see the article by Dorst et al. Cover image: Kaitlyn Dorst and Steve Ramirez.