This week, the brain cells that map where you are also know what you're listening to.

A neuron that during spatial navigation might be active in the northeastern corner of the room

would instead be active at C-sharp.

And how trade is draining the world's groundwater supplies.

In some parts of India, it might be just one or two decades

that it's going to become impossible to use it. Plus a new compound that can harvest the sun's

energy and keep the costs down. This is the nature podcast for March the 30th 2017. I'm

Kerry Smith. And I'm Noah Baker.

If brain regions had catchphrases, the hippocampuses would be location, location, location.

For decades, neuroscientists have known that the hippocampus is active when a rat navigates its way through a maze, for instance, and studies of the hippocampus

in London taxi drivers show a boost in size that's linked to their exhaustive knowledge of the

city's streets. But a new study suggests that thinking of the hippocampus as purely a spatial

navigation hub is a bit one-dimensional, or, okay, two-dimensional. Neuroscientist Dmitri Aronov and his colleagues at Princeton University in New Jersey

thought they'd take the rats in their lab to a whole new dimension

and see how their hippocampus got on with sound.

Here's Dmitri.

We don't always navigate through physical space.

For example, a jazz musician navigates by transitioning between musical chords.

The relevant feature of experience for a jazz musician at any given point in time isn't spatial location. It's the musical chord that the musician is playing

at that moment in time.

So we essentially trained our rats

to play a very rudimentary musical instrument,

...