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A new study by researchers at Rockefeller University has revealed a class of neurons in the temporal pole region of the brain that connects facial perception to long-term memory.
The findings, published in the journal Science, are the first to explain how our brains inculcate the faces of those we hold dear.
“When I was starting out in neuroscience, if you wanted to ridicule someone’s argument, you dismissed it as ‘just another grandma’s neuron’ – a hypothesis that couldn’t exist,” said Winrich Freiwald, professor. of Neuroscience and Behavior at Rockefeller University.
“Now, in a dark and poorly studied corner of the brain, we have found the closest thing to a grandmother’s neuron: cells capable of connecting facial perception to memory,” he added. .
The idea of a grandmother’s neuron first appeared in the 1960s as a theoretical brain cell that on its own would encode a specific and complex concept. One neuron to remember his grandmother, another to remember his mother, etc. At its heart, the notion of a one-to-one relationship between brain cells and objects or concepts was an attempt to address the mystery of how the brain combines what we see with our long-term memories.
Scientists have since discovered many sensory neurons specializing in processing facial information and as many memory cells dedicated to storing data from personal encounters. But a grandmother’s neuron – or even a hybrid cell capable of connecting vision to memory – never emerged. “We expect that we are already done,” said Freiwald. “Far from it! We weren’t clear on where or how the brain processes familiar faces.”
Recently, Freiwald and his colleagues discovered that a small area in the temporal pole region of the brain may be involved in facial recognition. So the team used functional magnetic resonance imaging as a guide to zoom in on the TP regions of two rhesus monkeys and recorded the electrical signals from the TP neurons as the macaques looked at images of familiar faces (which they had seen in person) and unknown. faces they had only seen virtually, on a screen.
The team found that neurons in the TP region were highly selective, responding more strongly to faces that subjects had seen before than to unfamiliar faces. And the neurons were fast – distinguishing between known and unfamiliar faces immediately after image processing.
Interestingly, these cells responded three times more strongly to familiar faces than to unfamiliar faces, even though the subjects had actually seen the unfamiliar faces virtually several times, on screens. “It may indicate the importance of knowing someone in person,” said neuroscientist Sofia Landi, the article’s first author. “Given the current trend towards virtual, it’s important to note that the faces we have seen on a screen may not evoke the same neural activity as the faces we meet in person.”
The results are the first evidence of a hybrid brain cell, much like grandmother’s legendary neuron. Cells in the TP region behave like sensory cells, with reliable and rapid responses to visual stimuli. But they also act like memory cells that only respond to stimuli the brain has seen before – in this case, familiar individuals – reflecting a change in the brain as a result of past encounters.
“It’s these very visual and very sensory cells, but like memory cells,” Freiwald said. “We have discovered a connection between the sensory and memory domains.”
But cells are not, strictly speaking, grandmother’s neurons. Instead of a cell encoding a single familiar face, the cells in the TP region seem to work together, as a collective.
“It’s a ‘grandma’s facial area’ of the brain,” Freiwald said. The discovery of the TP region at the heart of facial recognition means that researchers can soon begin to study how these cells encode familiar faces.
“We can now ask ourselves how this region is connected to other parts of the brain and what happens when a new face appears,” Freiwald asked. “And of course we can start to explore how it works in the human brain.”
Going forward, the findings could also have clinical implications for people with prosopagnosia or blindness, a socially isolating disease that affects around one percent of the population.
“Blind people often suffer from depression. It can be debilitating because in the worst case scenario, they can’t even recognize loved ones,” Freiwald said. (ANI)
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