Only the salt-sensing brain cells get more active when salt is low—not other nearby cells—and they don’t get the signal from nerves in the gut, meaning they respond directly to hormones in the blood.

If you remove most of the salt-craving brain cells, mice no longer seek out salt—even when they’re very low on it.

When mice are low on salt, certain brain cells in the back of the brain start firing on their own like a heartbeat, thanks to special sodium channels, and this makes them crave salt.