With the tough job of trying to keep track of what’s going on in front of it, the brain relies not only on what it sees, but also a comparison with what it just saw. A new study in mice by MIT Neuroscientists in Science pinpoints the circuit that provides that service.

Certain friendly viruses called phages can be weaponized to fight even the most difficult bacterial infections. But to make phage therapy more effective against the antibiotic resistance crisis, first we need to better understand how bacteria fight phage invasion, and how phages fight back. In a new study, researchers identify a counter defense used by a group of phages common in the human gut that helps them stay one step ahead of their bacterial hosts.