To remain oriented in a complex world, our brains constantly make and revise maps of our surroundings. We do most of this mental mapping unconsciously, which makes it hard to study how our brains keep a firm grasp on space and time.

“Every creature, no matter how simple or complex, must make maps of space,” said Mayank Mehta, a neuroscientist at UCLA. “Our goal is to understand what are the cues they are using and how they are putting them together.”

To meet that goal, Mehta and his colleagues watched the brains of rats exploring a virtual reality environment and found that mental mapping relies on a wider variety of sensory input than previously thought.

That’s right—they put rats in virtual reality.

In the real world, it’s too hard to control all of the potential sensory stimuli, so to isolate the visual navigation cues, they put the rats in a virtual world that looked like a square room with cues on the walls. Each rat stood on a ball and wore a harness that held the rat in place. The ball floated in the air so the sophisticated microcomputer inside could record each step and generate and project the corresponding visual scene.

“They get the compelling illusion that they are moving,” Mehta said, but the only cues the rats had to work with were the visual scene and their body movements—no smells or sounds.

Most people believe that they spatially process their surroundings using visual cues, like buildings, landscape, and the positions of furniture. Turns out, that might only be half the story.

When the UCLA researchers compared the brain activity of the rats in the virtual reality to that of rats navigating a similar real-world environment, they found significant differences between the two. They found that the brain actually kept track of the number of steps the rats took. Previous research has demonstrated that individual neurons, called place cells, keep us oriented by keeping track of absolute position, firing at a specific locations in the environment. This research suggests that the neurons are actually keeping track of the relative distance in their environment.

The data also shows that non-visual cues play an important role in building mental maps. Mehta said that even though people think they are ignoring the smell of the garbage can they walk past or the shifting sound of traffic, these non-visual cues account for about half of mental mapping. “We think that we are not paying attention, but our brain is,” Mehta said.

Understanding how we build mental maps is a key component of the ongoing quest to understand how we learn and remember. The region of the brain that generates our maps, the hippocampus, is also the region damaged by Alzheimer’s and PTSD, suggesting that mental orientation is fundamental part of healthy brain function. We tend to take our mental maps for granted, no doubt because our healthy brains can make them effortlessly, but we’d be truly lost without them.

“There is nothing that happens that is not in space or time.” Mehta said. “This whole edifice of memory may be rooted in space.”

Science, 2013 DOI: 10.1126/science.1232655 (About DOIs).