Penn research adds new dimensions to understanding spatial memory
The brain has a complex system for keeping track of which direction a person is facing as he or she moves about; remembering how to get from one place to another would otherwise be impossible.
Penn psychologists have now shown a neurological basis for something that researchers have long observed about navigational behavior: People use geometrical relationships to orient themselves.
The research, which is related to the work that won this year’s Nobel Prize in Physiology or Medicine, adds new dimensions to our understanding of spatial memory and how it helps us to build memories of events.
“Imagine coming out of a subway stop—you know exactly where you are in the world, but you still have the experience of looking around to figure out which way you are facing,” says Marchette. “We’re interested in how people are able to reset their sense of direction in the world and what cues they rely upon in the environment to do that.”
The researchers attacked this problem using a memory test based on a virtual environment with a precisely designed layout. The environment consisted of a park with four museums, each of which contained eight unique items. Each museum was visually distinct and faced different directions, but all had identical layouts in terms of their objects’ locations. The objects were also set in alcoves, meaning they could only be seen from one direction.
After participants memorized the objects’ locations, they entered an MRI machine. There, the researchers scanned a region of their brains known as the retrosplenial cortex while asking whether a given object was to the left or right of another object in the same museum.
They found that an individual’s brain patterns were similar across instances where they imagined looking at objects that have the same relationship to the surrounding room, regardless of which room it was or the “true” direction they were facing. For example, remembering objects on the back walls of two different museums produced similar activation patterns, even though the back wall is north in one museum and east in the other.
Critically, the similarities between these patterns meant that participants weren’t remembering the individual museums themselves, but rather their orientations within them.
“We can even reconstruct the location the participant is remembering based on those similarities,” Epstein says. “Once we know what we are looking for based on the first half of a participant’s responses, we can estimate the location of a given view entirely from the fMRI data.
“It’s as if we can read out a ‘floor plan’ of the museums from each person’s brain,” he adds. “And because the museums are geometrically identical, the retrosplenial cortex uses the same ‘floor plan’ for all of them.”