In a discovery that has applications ranging from self-driving cars to neurosurgery, Emory psychologists have found that three regions of the brain each perform distinct functions in helping humans navigate their environments.
The human brain’s navigation of an environment was previously understood as a task performed by three cooperating regions of the brain. Using a virtual town called “Neuralville,” Emory psychologists found that these three regions — the parahippocampal place area (PPA), retrosplenial cortex (RSC) and occipital place area (OPA) — possess distinct functions that allow us to navigate environments.
In a paper published by the Proceedings of the National Academy of Sciences, Associate Professor of Psychology Daniel Dilks and first author and “Neuralville” creator Andrew Persichetti, who worked in Dilks’ lab as a graduate student, found that the PPA recognizes specific locations of which the RSC creates mental maps. Previous research has shown that the OPA contributes to the navigation of immediate surroundings.
“If you’re in a dorm room, and I asked you [to] walk around that immediate surrounding, the OPA plays a role in that ability,” Dilks said. “The PPA enables you to tell me that you’re in a room and not a kitchen.”
Dilks said that while it makes intuitive sense that the three regions would work together for navigation, the belief lacked substantive evidence. Through their study, Dilks and Persichetti aimed to show that only the RSC and OPA, and not the PPA, are involved in navigation.
“There hadn’t been direct evidence of [all three regions working together], so I was asking that question: are they all indeed involved in navigation?” Dilks said. “So we put that hypothesis out there, [the hypothesis] that no, they are not all involved in navigation like people think.”
Participants of the study were tasked with exploring “Neuralville” from a first-person perspective through a computer screen. This stage of the study was meant to familiarize participants with the town’s layout. “Neuralville” is symmetrical, structured around a central park and divided into four quadrants, each of which houses two buildings of different categories. The building categories include coffee shops, gyms, dental offices and hardware stores, of which the town contains two each.
Once participants were completely familiarized with the town, they were shown images of various buildings in the town and asked to identify their location and type until they could correctly identify every building in the town. The same process was repeated with participants in a functional MRI machine, where the regions of the brain relevant to the study were shown to respond to each image based on their purpose.
Dilks said that Persichetti made the town symmetrical in order to dissociate the regions of the brain that they hypothesized had different purposes. In other words, researchers were able to more easily identify which regions of the brain reacted to building location and which reacted to category.
“There were two kinds of buildings in each quadrant so we could get location without categorization,” Dilks said. “Now we needed the [category] of building, so [Persichetti] put a dentist office in the northwest and southwest. We could dissociate what brain regions were responding to kinds of buildings in the same location or the same kind of building in different locations.”
Dilks aims to continue his research and show total independence between the three navigational regions of the brain. He plans to conduct further experiments using a transcranial magnetic stimulation machine, which sends an electric pulse into specific brain regions and allows for their temporary dissociation.
“Here is a thought experiment: if I’m in a new environment, I don’t have to know what kind of place it is in order to navigate it,” Dilks said. “I want to claim you don’t need the recognizer to navigate.”
Dilks said that a deeper understanding of human navigation will be significant for the field of neurosurgery.
“We’re starting to map the brain,” Dilks said. “It’s totally applicable for [the] neurosurgeon world to know what parts of the brain are involved in what kinds of functions. You can’t fix a system if you don’t know how it functions.”
