Northwestern researchers have found that the mouse brain can draw a mental map of the world based only on smell.

Neurobiology graduate student Brad Radvansky and neurobiology Prof. Daniel Dombeck developed a virtual reality “landscape” with a different smell at every location in a virtual track. They discovered that mice could navigate the virtual world based solely on smells, which could lead to a fuller understanding of the ways odors can guide animal behavior.

The study was published Feb. 26 in the journal Nature Communications, according to a news release.

“Odor-guided behaviors are very important for animals, and every organism that can move can use chemicals in space to guide its movements,” Radvansky told The Daily. “(This fundamental behavior has) been very difficult to study because odors … (are) very difficult to control in an experiment. You can imagine an odor in a room. It’ll just diffuse all over the place.”

Dombeck said the study’s key takeaway was the ability to “very rapidly and precisely” control the odors an animal smelled, enabled by the odor-based virtual reality system they developed. Through virtual reality, the team could define the animal’s environment so that the only thing telling the animals their location was their sense of smell, he added.

In the experiment, a mouse ran on a Styrofoam ball and smelled odors blown quickly onto its nose, Radvansky said. The mouse, facing a screen, ran up and down a virtual reality track, he added, with the ball acting like the mouse’s video game controller.

“It’s all in virtual reality, so the mouse doesn’t actually go anywhere,” Radvansky said. “It just sees that it goes somewhere on a screen and smells that it goes somewhere new.”

Even after the screen was turned off, the mouse could still navigate in virtual reality using only its sense of smell, Radvansky said.

The researchers used bubblegum and pine smells, and changed the balance of the odors depending on the mouse’s location within the virtual world, Radvansky said. He added that the team avoided scents like cat urine, to which mice would have an “innate response.”

The team also found that some of the “neural mechanisms” responsible for navigating using smell were the same as the ones used when mice navigated by sight, Radvansky added.

“We were able to … identify the part of the brain that’s activated during navigation and show it’s activated in the same way using odors as it was for using visual cues,” Dombeck said.

Though the study focused on mice, its results could potentially have implications for human brains, which have many similarities to mouse brains, Dombeck added.

Radvansky said their system could also be applicable to virtual reality technology, which currently focuses on vision and sound. Odor in virtual reality has not really been explored, he added.

Radvansky said he is interested in the question: “What is ‘space’ really made out of?”

“We sense different features of the world with our eyes and our ears and our noses, but there’s no variable that we detect directly that is called ‘space,’” Radvansky said. “In this experiment, we showed that if the world is made out of just smell, you can still have a map of space in your brain.”

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