The decoding of a brain region that distinguishes one face from another may offer clues to the very nature of consciousness.
In the spring of 1995, Nancy Kanwisher was granted access to the functional magnetic resonance imaging (fMRI) machine at the Massachusetts General Hospital. After making little headway using the nascent technology to explore the visual perception of shape, she climbed inside the machine, gazed at photos of people’s faces, and had her coworkers scan her brain.
What Kanwisher discovered would launch a 30-year journey to unravel how humans perform a vital social task: making sense of each other’s faces. Those early experiments revealed a small patch of increased blood flow in a brain region that responded more vigorously to images of faces than random objects. That first scan showed “a promising blob on the bottom of my right hemisphere,” Kanwisher writes in a 2017 retrospective about the work. To be certain, she had her colleagues scan her again and again. “To our delight, the trusty little blob showed up in exactly the same place every time.”
Like other seminal discoveries, Kanwisher’s finding made sense in hindsight. Faces hold a special significance for us and for our primate relatives. “We are social creatures,” says Winrich Freiwald, of The Rockefeller University, who joined Kanwisher’s lab as a postdoc in 2001. “Faces are so important for those social interactions that finding a specialized circuitry for faces seemed a safe bet.”
In the decades since Kanwisher, now at MIT, spotted that first, promising blob, that bet has paid off in spectacular fashion. Discovery of these face-specific systems in humans and monkeys launched an intensive avenue of research that has deconstructed how the brain identifies and analyzes faces. In 2024, the groundbreaking work earned Kanwisher, Freiwald, and Doris Tsao of the University of California, Berkeley, the 2024 Kavli Prize in Neuroscience.
“Nancy Kanwisher is a real pioneer: Her original paper has about 7,000 citations, which is just astronomical,” says neuroscientist Bruno Rossion of the University of Lorraine in France, who studies face recognition in humans and did not participate in the work. “And she has since taken a leading role in defining the function of these regions in human face recognition.”
Tsao and Freiwald’s subsequent work localizing the equivalent face-specific regions in monkeys and then recording the activity of individual neurons in that network with electrodes “changed the field and allowed them to make real progress in understanding how these neurons were coding for various properties of faces”, Rossion says.
A neural code
Kanwisher’s findings were particularly exciting since they demonstrated that the brain’s architecture could be functionally compartmentalized. “This question had been debated heatedly in our field for nearly 200 years,” she writes in her 2017 retrospective. “And now here was a little piece of the brain that seemed to do just one thing: perceive faces.”
Deciphering how the cells within this patch perform this remarkable feat, however, was not easy to do in the human brain, where low-resolution fMRI imaging could only detect the collective response of hundreds of thousands of neurons. That’s where Tsao and Freiwald come in...
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