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.

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

The brain uses two different signals to control salt craving: one slow signal that says 'we need salt' and one fast signal that says 'you tasted salt, stop now'—and they work together to make the mouse eat just enough.

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.

The salt-craving brain cells connect directly to a specific spot in the brain called the vlBNST—turning on just that connection makes mice drink salt water, even without other triggers.