Scientists discover a new class of memory cells for remembering faces
Date:
July 1, 2021
Source:
Rockefeller University
Summary:
Our brains have sensory cells, which process the faces that
we see, and memory cells dedicated to storing data from person
encounters. But until now, a hybrid neuron capable of linking
vision to memory -- and explaining how we recall familiar faces --
remained elusive.
FULL STORY ========================================================================== Scientists have long searched in vain for a class of brain cells that
could explain the visceral flash of recognition that we feel when we see
a very familiar face, like that of our grandmothers. But the proposed "grandmother neuron" -- a single cell at the crossroads of sensory
perception and memory, capable of prioritizing an important face over
the rabble -- remained elusive.
==========================================================================
Now, newresearch reveals a class of neurons in the brain's temporal pole
region that links face perception to long-term memory. It's not quite
the apocryphal grandmother neuron -- rather than a single cell, it's
a population of cells that collectively remembers grandma's face. The
findings, published in 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," says Winrich Freiwald, professor
of neurosciences and behavior at The Rockefeller University.
"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." Have I seen that face before? The idea of a grandmother neuron 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.
========================================================================== 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. "The expectation is that we would have had this down by
now," Freiwald says. "Far from it! We had no clear knowledge of where
and how the brain processes familiar faces." Recently, Freiwald and
colleagues discovered that a small area in the brain's temporal pole
region 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 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 team 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. "This may point to
the importance of knowing someone in person," says neuroscientist Sofia
Landi, first author on the paper.
"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." A tapestry of grandmothers The findings constitute the first evidence of a hybrid brain cell, not unlike
the fabled 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 which 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. "We
have discovered a connection between the sensory and memory domains."
==========================================================================
But the cells are not, strictly speaking, 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 says.
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.
"We can now ask how this region is connected to the other parts of the
brain and what happens when a new face appears," Freiwald asks. "And of
course, we can begin exploring how it works in the human brain." In the future, the findings may also have clinical implications for people
suffering from prosopagnosia, or face blindness, a socially isolating
condition that affects about one percent of the population. "Face-blind
people often suffer from depression. It can be debilitating, because in
the worst cases they cannot even recognize close relatives," Freiwald
says.
"This discovery could one day help us devise strategies to help them." ========================================================================== Story Source: Materials provided by Rockefeller_University. Note:
Content may be edited for style and length.
========================================================================== Journal Reference:
1. Sofia M. Landi, Pooja Viswanathan, Stephen Serene, Winrich
A. Freiwald. A
fast link between face perception and memory in the temporal pole.
Science, 2021; eabi6671 DOI: 10.1126/science.abi6671 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2021/07/210701140929.htm
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