About-Face: From ‘Grandmother Neurons’ to New Forms of Facial Recognition

The Problem: For decades, scientists have grappled with the mystery of facial recognition: how our brains turn visual information into memories. At one time, many hypothesized that individual brain cells store information about individual faces in a one-to-one ratio, but they were never able to prove the existence of these specialized cells.

The Study: Rather than a single cell that stores information to recognize a single face, it is a collection of neurons in a region of the brain called the temporal pole (TP) that links facial recognition to memory, finds a new study in Science by NYSCF – Robertson Neuroscience Investigator Alumnus Winrich Freiwald, PhD, of The Rockefeller University. This study also reveals the central role of TP cells in differentiating familiar versus unfamiliar faces in monkeys.

Why it Matters: This study is the first evidence of a hybrid brain cell that processes both visual and sensory information. The research also has implications for the treatment of facial prosopagnosia (face blindness), a neurological disorder that affects one’s ability to recognize even intimately familiar faces.

The Elusive ‘Grandmother Neuron’

Have you ever wondered how your brain can instantly pinpoint faces of people you’ve met, even if the encounter was years or decades ago? Humans have an extraordinary capacity for remembering faces of loved ones, friends, and even casual acquaintances, but the mechanisms behind this complex neural process have long remained undefined. 

In the 1960s, scientists proposed one possible answer as to how humans recognize faces: a cell type called the “grandmother neuron.” The central idea was that for each face someone encounters, there is a single cell that encodes information about it. The activity of a neuron would map to one object — the face of your grandmother, for instance — and draw up memories related to that person. However, scientists were never able to find out if these grandmother neurons exist, relegating this cell to the realm of scientific myth.  

“When I was coming up in neuroscience, if you wanted to ridicule someone’s argument you would dismiss it as ‘just another grandmother neuron’ — a hypothetical that could not exist,” Dr. Freiwald, a professor of neurosciences and behavior, said in a press release. 

Now, scientists from the Freiwald lab may have found the next best thing. 

How the Brain Thinks “Face to Face”

“In an obscure and understudied corner of the brain, we have found the closest thing to a grandmother neuron: cells capable of linking face perception to memory,” said Dr. Freiwald. 

Previous research in Dr. Freiwald’s lab showed that the temporal pole (TP) region of the brain is involved in the recognition of familiar faces. For this study, the group decided to investigate further and conduct electrical scans with a technique called functional magnetic resonance imaging (fMRI) on two rhesus macaque monkeys, focusing on TP neuronal activity. 

The scientists showed the monkeys a series of two hundred images that included human faces, monkey faces, bodies, and objects, while measuring activity of cells in the TP. Out of the data came two striking results. 

First, researchers found that TP neurons became more active when the monkeys were shown faces of other monkeys, as opposed to human ones. 

Second, the neurons were far more responsive to images of familiar monkeys than unfamiliar ones. If one monkey met another one “in person” and was later shown an image of that second monkey’s face, its TP cells would instantly recognize the face and respond accordingly. In fact, neuronal activity within this region was three times higher for familiar monkeys versus those the monkey had only seen virtually. Further analyses also indicated that TP neurons could also distinguish between faces of familiar monkeys, but not unfamiliar ones. 

These surprising results indicate the importance of in-person interactions for establishing links from vision to memory.

“Given the tendency nowadays to go virtual, it is important to note that faces that we have seen on a screen may not evoke the same neuronal activity as faces that we meet in-person,” noted first author Sofia Landi, PhD.

Facing the Future

“These are very visual, very sensory cells — but like memory cells. We have discovered a connection between the sensory and memory domains,” remarked Dr. Freiwald. “We can now ask how this region is connected to the other parts of the brain and what happens when a new face appears. And of course, we can begin exploring how it works in the human brain.”

One potential application of this work is in the treatment of face blindness, a disorder that affects millions worldwide, leaving them unable to recognize the faces of their friends or family. As one may imagine, this has an enormous impact on everyday life and can lead to social isolation and depression.

“This discovery could one day help us devise strategies to help [patients],” said Dr. Freiwald, noting that “[Face blindness] can be debilitating, because in the worst cases, patients cannot even recognize close relatives.”

Certainly, there are plenty of future directions to follow. If scientists were able to find one population of brain cells that collectively process visual data and turn it into memories, then it is possible that similar groups exist in nearby regions of the brain. These groups might then form the foundation of more complex systems that turn our lived experiences into the greatest of gifts — our memories.

Journal Article:

A fast link between face perception and memory in the temporal pole
Sofia M. Landi, Pooja Viswanathan, Stephen Serene, Winrich A. Freiwald. Science. 2021. DOI: 10.1126/science.abi6671

Cover image credit: The Rockefeller University