July 16, 2021: That flash of familiarity we feel when we see someone we know has long fascinated and puzzled scientists, who have not been able to determine precisely what is happening in the brain. But for the first time, researchers now reporting a new class of cells they say is responsible.
The discovery runs counter to the prevailing neuroscience understanding that various areas of the brain must communicate with each other to process information. Instead, this study shows that a region of the brain appears to be working for the sole purpose of identifying the people we know.
It was thought that a single brain cell, called a grandmother’s neuron, would be discovered because of its ability to identify familiar faces, such as a person’s grandmother, but that has yet to happen.
The problem is so ingrained in neuroscience that lead author Winrich Freiwald, PhD, professor of neuroscience and behavior at Rockefeller University in New York City, says that when one scientist wants to ridicule another’s argument, he dismisses it as “just another grandmother’s neuron, “or unproven theory.
Now, in a dark and poorly studied 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 the cells
For their study, Freiwald and his colleagues recorded electrical signals from neurons in the brains of two rhesus monkeys while they were shown photos of faces; some of the people they knew and some of the people they didn’t.
The team showed that neurons in the lower front part of the brain, the temporal pole, play a role in identifying familiar faces and in the ability to differentiate between familiar and new faces.
In fact, neural responses were three times stronger for the faces of people the monkeys were familiar with than for the 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 meeting someone in person, the researchers explain. Given the current tendency to interact virtually, we must be aware that the faces we have seen on a screen may not evoke the same neural activity as the faces we meet in person.
With this information, scientists can begin 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.