Brain Quenches Thirst Long Before Body Hydrates

When you’re dehydrated, your brain instructs you to drink fluids. Almost immediately after drinking fluids, your thirst disappears—but your body hasn’t had enough time to absorb the liquid. So, what compelled you to stop drinking?

Yuki Oka and his colleagues at California Institute of Technology have been researching the thirst center, a small part of the brain. Researchers have known about this region for decades, but precisely how it worked remained a mystery.

It takes 10 to 15 minutes for the body to hydrate, so it’s surprising that animals stop drinking water within one minute—well before their body becomes hydrated.

But as new tools and technologies emerge, researchers can now manipulate specific brain circuits to understand how they operate. Oka was able to identify cells in the thirst center that would become active if a mouse was drinking, but not if it was eating. Here’s Jon Hamilton reporting for NPR:

The ability is remarkable because both activities use the same muscles in the throat, Oka says. He suspects that the cells can tell the difference between the fast muscle movements of gulping and the slower pace of chewing and swallowing.

The team also showed that these specialized brain cells were part of a circuit that could switch off the brain’s thirsty signal. “If we stimulate those neurons in [a] thirsty animal, you can completely stop [it from] drinking water,” he says.

It takes 10 to 15 minutes for the body to hydrate, so it’s surprising that animals stop drinking water within one minute—well before their body becomes hydrated. The brain somehow alerts the body that thirst-relief is on the way. Stopping is also important because drinking large amounts of water is unhealthy.

This research could help with psychogenic polydipsia: a rare disorder that causes people to drink a dangerous amount of water. In the long run, by understanding the brain circuitry behind basic functions, researchers hope to learn how to manipulate circuits involved in psychiatric disorders like depression and schizophrenia.