Scientists in the US might have found an answer to how our brain cells work to remember and recognise a familiar face. Findings from a new study, led by researchers at the Rockefeller University, have revealed a class of neurons -- or brain cells -- in the temporal pole region that links face perception to long-term memory.
These findings, published recently in the journal Science, are the first to explain how our brains inculcate the faces of those we hold dear.
"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," Winrich Freiwald, professor of neurosciences and behaviour at The Rockefeller University, explains in a news release.
"Now, 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," he added.
The idea of a grandmother neuron, the release explains, first showed up in the 1960s -- as a theoretical brain cell that would code for a specific, complex concept, all by itself.
One neuron for the memory of one's grandmother, another to recall one's mother, and so on. At its heart, the notion of a one-to-one ratio between brain cells and objects or concepts was an attempt to tackle the mystery of how the brain combines what we see with our long-term memories, the release adds.
Scientists have since discovered plenty of sensory neurons that specialize in processing facial information and as many memory cells dedicated to storing data from personal encounters. But a grandmother neuron- or even a hybrid cell capable of linking vision to memory -- never emerged.
Recently, Freiwald and colleagues discovered that a small area in the brain's temporal pole or TP region may be involved in facial recognition. So, the team used functional magnetic resonance imaging (MRI) as a guide to zoom in on the TP regions of two rhesus monkeys and recorded the electrical signals of TP neurons as the macaques watched images of familiar faces (which they had seen in-person) and unfamiliar faces that they had only seen virtually, on a screen.
The researchers found that neurons in the TP region were highly selective, responding to faces that the subjects had seen before more strongly than unfamiliar ones. And the neurons were fast -- discriminating between known and unknown faces immediately upon processing the image.
Interestingly, these cells responded threefold more strongly to familiar over unfamiliar faces even though the subjects had in fact seen the unfamiliar faces many times virtually, on screens, the release adds. "This may point to the importance of knowing someone in person," said neuroscientist Sofia Landi, the paper's first author. "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."
The findings constitute the first evidence of a hybrid brain cell, not unlike the grandmother neuron. The cells of the TP region behave like sensory cells, with reliable and fast responses to visual stimuli. But they also act like memory cells that respond only to stimuli that the brain has seen before- in this case, familiar individuals- reflecting a change in the brain as a result of past encounters.
"They're these very visual, very sensory cells- but like memory cells," Freiwald says in the release. "We have discovered a connection between the sensory and memory domains."
But the cells are not exactly grandmother neurons. Instead of one cell coding for a single familiar face, the cells of the TP region appear to work in concert, as a collective.
"It's a 'grandmother face area' of the brain," Freiwald said. The discovery of the TP region at the heart of facial recognition means that researchers can soon start investigating how those cells encode familiar faces.
(With inputs from agencies)