The ability to recognize familiar faces depends on a neural code shared between brains

The ability to recognize familiar faces is fundamental for social interaction. This process provides visual information and activates social and personal knowledge about a person who is familiar. But how the brain processes this information between participants has long been a question. Distinct information about familiar faces is encoded in a neural code that is shared between brains, according to a new study from Dartmouth published in the Proceedings of the National Academy of Sciences.

“In the areas of visual processing, we have found that information about personally familiar and visually familiar faces is shared in the brains of people who have the same friends and acquaintances,” says first author Matteo Visconti di Oleggio Castello, Guarini ‘ 18, who conducted this research. as a graduate student in Psychological and Brain Sciences at Dartmouth and is now a Postdoctoral Fellow in Neuroscience at the University of California at Berkeley. “The surprising part of our findings is that the information shared about personally familiar faces also extends to areas that are non-visual and important for social processing, suggesting that there is social information shared between brains.”

For the study, the research team applied a method called hyperalignment, which creates a common representational space to understand how brain activity is similar among participants. The team used data obtained from three fMRI tasks with 14 graduate students who had known each other for at least two years. In two of the tasks, participants received images of four other personally familiar graduate students and four other visually familiar people, who were previously unknown. In the third task, participants looked at parts of The Grand Hotel Budapest. The data from the film, which is publicly available, was used to apply hyperalignment and align participants’ brain responses in a common representational space. This allowed researchers to use machine learning classifiers to predict which stimuli a participant was looking at based on the brain activity of other participants.

The results showed that the identity of visually familiar and personally familiar faces was accurately decoded through the brain in areas that are primarily involved in visual processing of faces. Outside of the visual areas however, there wasn’t a lot of decoding. For visually familiar identities, participants only knew what the stimuli looked like; they did not know who these people were or had no other information about them.

By decoding personally familiar identities, the results demonstrated that there was much more information shared in the brains of the participants. There was high decoding accuracy in four other areas outside of the visual system: the dorsal medial prefrontal cortex, which is known to be involved in social processing (processing of the intentions and traits of others); the precuneus, an area that has been shown to be more active when treating personally familiar faces; the insula, which is known to be involved in emotional processing; and the temporal wall junction, which plays an important role in social cognition and in representing the mental states of others (also known as “theory of mind”).

“This shared conceptual space for the personal knowledge of others allows us to communicate with people we know in common,” says lead author Maria (Ida) Gobbini, Associate Research Professor in the Cognitive Science Program at Dartmouth and Associate Professor to the department. of Experimental, Diagnostic and Specialized Medicine at the University of Bologna.

Previous research by the team using fMRI experiments found that these “theory of mind” areas in the brain are activated when a person sees someone who is personally familiar to them. “When we see someone we know, we immediately activate who that person is,” says Gobbini. “This is what allows us to interact in the most appropriate way with someone who is familiar to us.” For example, the way you interact with a friend or family member may be very different from the way you interact with a coworker or boss.

It would have been quite possible for everyone to have their own private code to know what people are like, but they don’t. Our research shows that treating familiar faces really has to do with general knowledge about people. “

James Haxby, co-author, professor of psychological and brain sciences, Dartmouth