Summary: Combining neuroimaging and a constructed virtual reality town, researchers found the brain uses three different systems to perceive environment. One system allows us to recognize a place, another helps navigate through that location, and the third helps navigate from one place to another. The parahippocampal place area (PPA) helps encode location recognition, while the retrosplenial complex allows for mentally mapping the locations of specific places.
Source: Emory Health Sciences
Psychologists at Emory University have found that the human brain uses three distinct systems to perceive our environment — one for recognizing a place, another for navigating through that place and a third for navigating from one place to another.
For a new paper, they designed experiments involving a simulated town and functional magnetic resonance imaging (fMRI) to gain new insights into such systems. Their results, published by the Proceedings of the National Academy of Sciences (PNAS), have implications ranging from more precise guidance for surgeons who operate on the brain to better computer vision systems for self-driving cars.
“We’re mapping the functions of the brain’s cortex with respect to our ability to recognize and get around our world,” says Daniel Dilks, Emory associate professor of psychology and senior author of the study. “The PNAS paper provides the last big piece in the puzzle.”
The experiments showed that the brain’s parahippocampal place area is involved in recognizing a particular kind of place in the virtual town, while the brain’s retrosplenial complex is involved in mentally mapping the locations of particular places in the town.
These new results follow work published last year by the Emory researchers, showing that the brain’s occipital place area is involved in navigating through a particular place.
Before, some researchers theorized that all three of these cortical scene-selective regions — abbreviated as the PPA, RSC and OPA — were involved generally in navigation. “Our work continues to provide strong evidence that this theory is just not true,” Dilks says.
“We’re showing that there are specialized systems in the brain that play different roles involved with recognizing places and navigating,” adds first author Andrew Persichetti, who did the work as an Emory graduate student in the Dilks lab. He has since received his PhD in psychology and is now a post-doctoral fellow at the National Institute of Mental Health.
For the PNAS paper, Persichetti developed experiments based on a virtual town he created, called “Neuralville,” and a simple video game. “One of my favorite things about being a scientist is getting to design experiments,” he says. “It’s fun to try to come up with a clever, yet simple, way to answer a complex question.”
Neuralville consists of eight buildings, spread over four quadrants, or locations in the town, that surround a park. The categories of buildings are paired and include: Two coffee shops, two dentists’ offices, two hardware stores and two gyms. Each quadrant contains two buildings, but no quadrant contains two of the same category. And, although they can be paired by categories, location or facing direction, none of the eight buildings shares visual features, such as shape, size or texture.
Participants sat at a computer and became familiar with the town as they “walked” around the four quadrants by pressing the arrow keys on the keypad. They were then dropped into random locations of town and given tasks such as “Walk to Coffee Shop A.” After about 15 minutes of this practice, they were shown images of each building and asked what type it was and which quadrant of the town it was located in.
Once a participant scored 100 percent on this quiz, they were then put into an fMRI scanner. As their brains were scanned, they were given a picture of one of the buildings, such as Coffee Shop B, and asked a question. For example: “If you’re directly facing Coffee Shop B, would Dentist Office A be to your right or to your left?”
The participants repeated the task 10 times as the fMRI recorded activity in the PPA and the RSC. The brain data was rendered in units called “voxels,” which are similar to pixels, except they are three-dimensional.
The results showed that the pattern of responses in the RSC were more similar for buildings that shared the same location than for buildings of the same category. The opposite was true for the pattern of responses in the PPA.
“These multi-voxel patterns reveal a spatial representation of these buildings in the RSC, and a categorical representation in PPA,” Persichetti says. “The RSC patterns basically puts them on a map in their proper locations, while the PPA pattern instead clusters them by their category.”
Clinical applications for the research include better brain rehabilitation methods for those with problems related to scene recognition and navigation.
The research may also prove beneficial to improving computer vision systems, such as those for self-driving cars. “Through evolution, the brain has figured out the optimal solution to recognizing scenes and navigating around them,” Dilks says. “And that solution appears to be one of specializing the different functions involved.”
Dilks is a leader in mapping how the visual cortex is functionally organized. In 2013, he led the discovery of the OPA. In 2018, Dilks and Persichetti demonstrated that the OPA specializes in navigating through a particular place.
“While it’s incredible that we can show that different parts of the cortex are responsible for different functions, it’s only the tip of the iceberg,” Dilks says. “Now that we understand what these regions of the brain are doing we want to know precisely how they’re doing it and why’re they’re organized in this way.”
Funding: The PNAS research was funded by the National Eye Institute and a National Science Foundation Graduate Research Fellowship.
Emory Health Sciences
Carol Clark – Emory Health Sciences
The image is credited to Andrew Persichetti.
Original Research: Closed access
“Distinct representations of spatial and categorical relationships across human scene-selective cortex”. Andrew S. Persichetti and Daniel D. Dilks.
Distinct representations of spatial and categorical relationships across human scene-selective cortex
We represent the locations of places (e.g., the coffee shop on 10th Street vs. the coffee shop on Peachtree Street) so that we can use them as landmarks to orient ourselves while navigating large-scale environments. While several neuroimaging studies have argued that the parahippocampal place area (PPA) represents such navigationally relevant information, evidence from other studies suggests otherwise, leaving this issue unresolved. Here we hypothesize that the PPA is, in fact, not well suited to recognize specific landmarks in the environment (e.g., the coffee shop on 10th Street), but rather is involved in recognizing the general category membership of places (e.g., a coffee shop, regardless of its location). Using fMRI multivoxel pattern analysis, we directly test this hypothesis. If the PPA represents landmark information, then it must be able to discriminate between 2 places of the same category, but in different locations. Instead, if the PPA represents general category information (as hypothesized here), then it will not represent the location of a particular place, but only the category of the place. As predicted, we found that the PPA represents 2 buildings from the same category, but in different locations, as more similar than 2 buildings from different categories, but in the same location. In contrast, another scene-selective region of cortex, the retrosplenial complex (RSC), showed the exact opposite pattern of results. Such a double dissociation suggests distinct neural systems involved in categorizing and navigating our environment, including the PPA and RSC, respectively.