July 16, 2021 -- That flash of familiarity we feel when we see someone we know has long fascinated and stumped scientists, who have been unable to pinpoint what is happening in the brain. But for the first time, researchers are now reporting a new class of cells they say is responsible.
The discovery goes against the prevailing understanding in neuroscience that diverse areas of the brain must communicate with each other to process information. Instead, this study shows that one region of the brain appears to be operating for the sole purpose of identifying people we know.
It was thought that a single brain cell -- called the grandmother neuron, because of its ability to identify familiar faces, like a person's grandmother's -- would be discovered, but that has yet to happen.
The problem is so entrenched in neuroscience that senior author Winrich Freiwald, PhD, a professor of neurosciences and behavior at the Rockefeller University in New York City, says that when one scientist wants to ridicule another's argument, they dismiss it as "just another grandmother neuron," or unproven theory.
Now, in an obscure and understudied area of the brain, Freiwald says they have found the closest thing to a grandmother neuron in cells capable of linking face perception to memory.
The Grandmother of Cells
For their study, Freiwald and his colleagues recorded electrical signals from neurons in the brains of two rhesus monkeys as they were shown photos of faces; some of the people they knew, and some of the people they did not.
The team showed that neurons in the lower front of the brain, the temporal pole, play a role in the identification of familiar faces and the ability to tell the difference between known and new faces.
In fact, neuronal responses were three times stronger for faces of people the monkeys were personally familiar with than for faces of those they did not know, even if they had seen those faces multiple times on screens.
This could point to the importance of knowing someone in person, the researchers explain. Given the tendency nowadays to interact virtually, we must be aware that faces we have seen on a screen might not evoke the same neuronal activity as faces we meet in person.
With this information, scientists can start to investigate how these brain cells encode familiar faces. The researchers say they can now ask how this region is connected to the other parts of the brain and what happens when a new face appears.