Flickr/cadencrawford

A mix of imagination and memories of the physical shape of your surroundings helps orient you when you're lost.

Perhaps you know what it's like to be a flâneur. Without a goal or destination in mind, you walk easily for miles past your familiar city zone, not entirely sure which way you'll return.

But when it is time to head home, perhaps you've also had the experience of brief disorientation. You end up in square where you've been before, but it looks a lot like others you've seen, forcing you to pause a minute to remember which way to head. Was it down the wide street towards the back of the square, or that alleyway to the left? Ah, yes, the alley. And you're off.

Yet how, neurologically, do you recall this information? What are the cues that help your brain retrieve the right way to head?

"Navigation is something that's so easy for people to do, but we have a really hard time talking about what we're actually doing," says Steven Marchette, a postdoctoral fellow at the University of Pennsylvania's Department of Psychology. "You always know where you are until you suddenly don't."

Marchette is the lead author on a paper published in Nature Neuroscience this month that examines how the brain keeps track of "heading"—essentially, which way you're facing. Along with researchers Lindsay K. Vass, Jack Ryan, and Russell A. Epstein, Marchette found that your brain relies on a memory of the physical shape of your surroundings to gain orientation, before you make a turn.

This is related but different from the work recently awarded the Nobel Prize in Physiology of Medicine. Those researchers were looking at the specific neurons that encode mental "maps" of your environment, and how to navigate it step by step. Marchette and his colleagues looked at how a particular region of the brain, the retrosplenial complex (RSC), processes this one step of orientation.

To do so, the team conducted an experiment where subjects navigated a virtual environment: A park, approachable only from the south, with four museums laid out like a cloverleaf. Each entryway faced the center of the park, and each back wall facing a different cardinal direction. Though each museum was visually distinct, they were identical in layout and geometry, with the same eight alcoves containing different everyday objects. The layout is shown to the left.

Subjects were asked to explore the environment, then memorize the location of the objects on display. A few days later, the researchers scanned the subjects' brains as the subjects recalled the spatial relationships between the objects in different museums; for example, "The computer was to the left of the bicycle," or "The car was X in relation to the birthday cake."

Even if one museum faced to the west, the subjects remembered the orientation of the objects in it the same way that they remembered the objects in another museum that may have faced to the east. More than cardinal direction or a memory of the particular features of each museum, the RSC of each subject anchored onto the geometry of the museums in order to determine which way they had been facing.

"Our study is not so much about navigating in real time, or walking from one object to another," says Marchette. "It's letting us say something about how our imagination works—how you imagine yourself in a familiar places, and then how you orient yourself from there."

The RSC is critical for this "heading" function, say the researchers, and works alongside regions of the brain committed to other steps of navigation. "We know there's also a global sense of orientation in our brain that forms a neural compass," says Epstein. "As you move around, you have a sense of absolute direction you keep updating. What we're interested in, is when you're disoriented, what's the part of the brain that allows you to reorient yourself, and how does it do it?"

The next step, say the researchers, is to hone in on what specifically the RSC recognizes as geometric cues: Walls? Floorplan? Large landmarks? All of this will contribute to a greater understanding of how the brain processes navigation.

“Psychologists have long surmised that geometry is important for this kind of memory,” Epstein told the University of Pennsylvania, “but this is beginning to show the neurological basis for it. We hope this opens the door for a deeper look at this region of the brain.”

For your own deeper look, here's an overview of the study in video:

Top image courtesy of Flickr user cadencrawford.

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