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You’re probably familiar with that flash of recognition that happens when you see a person
and suddenly realize it is someone you know. And whether that makes you smile joyfully or
desperately avoid eye contact, this is part of everyday life.
So, you might never have thought twice about it. But neuroscientists have been trying to understand
exactly how our brains do this for years. And in the last couple of decades, researchers
have been closing in on an answer… and their findings offer us new clues about the neural
machinery behind our human nature. Now, the fact that you recognize, say,
your neighbor, or your mom, or the person you wake up beside in the morning might not
sound like anything special. Turns out, though,
it is no small feat for your brain. To recognize someone, your eyes have to scan their
face, and then your brain has to link that image to a specific person in its trove of memories.
Even if you’re looking at a blurry picture of your friend taken at a weird angle fifteen years ago,
your brain links that to the same memory that it pulls up when you see your friend
in real life at a party today. But if you don’t know a person,
your brain has a much harder time identifying two different images of them.
For decades, neuroscientists have been trying to understand why we respond to familiar faces
so differently from unfamiliar faces. And to get at that question, they’ve been
looking for what connects our perception of a face to our memory of a person.
One hypothesis that goes back to the 1960s centers on what’s called the grandmother neuron.
This is a hypothetical neuron that would fire any time you saw your grandma,
thought about your grandma, or even saw your grandma’s name. Basically, it’s a neuron that
encapsulated your entire concept of “grandma.” The idea was that we all have a neuron like this
for every single person that we know, and it’s that neuron that is the mysterious link between
our perception and memory of a person. But the concept of the grandmother neuron
actually started out as a joke—not a real-life scientific hypothesis.
Like: “Yeah, you totally have one special neuron that remembers your grandma; better not lose it.”
But while this idea is almost certainly an oversimplification, over time, some
research studies actually supported the general concept of a grandmother neuron, and it went
from a laughable idea to a serious hypothesis. For instance, in 2005, researchers studied the
brain activity of several areas of the brain in eight participants while they looked at pictures,
drawings, and names. And they showed that the subjects had specific groups of neurons
in the hippocampus that responded to pictures of Jennifer Aniston.
They also had specific groups of neurons that responded to pictures of Halle Berry
both in and out of costume—and the same group of neurons responded to
a string of letters spelling her name. So that suggests that while there might
not be a single grandmother neuron, there might at least be a group of grandmother neurons. And
Halle Berry neurons, and so on. Then, in the summer of 2021,
researchers from Rockefeller University published a study that seemed to identify
another piece of the puzzle linking our face perception and memory.
Rather than look for precise brain cells responding to specific faces,
their study looked at how the brain responded to unfamiliar versus familiar faces in general.
In a previous study on macaques, the team had found a small region of the brain
known as the temporal pole that seemed to respond to familiar faces.
So in this study, they stuck with macaques, which have similar networks
for processing faces to humans and are easier to study, and they zoomed in on that area.
The researchers showed two macaques over 200 images. They included the faces of monkeys they’d
personally known for a long time, monkeys they’d only ever seen on a screen, and monkeys that were
totally unfamiliar. They also included some human faces and other non-monkey objects as a control.
And the authors found that the cells in the monkeys’ temporal pole responded
any time they saw the face of a monkey they knew personally—and only then.
That suggests that there’s a specific region of the brain
that lets us know in a flash if a face is familiar or not. Which is exciting for a few reasons.
While this didn’t exactly find a grandmother neuron in the traditional sense of the term,
it did find a new class of neuron that seems to bridge perception and memory. And that
could be a big step toward understanding how our brains encode familiar faces.
It also tells us that, if human brains work anything like macaques’ brains, personally
knowing someone has an important effect on how we perceive and recognize them… on a cellular level.
In the end, although the grandmother neuron itself may not exist, the search for something
like it has given us lots of insight into the architecture behind some of our most
mundane but important social interactions. Speaking of the familiar, listening to some
of your favorite sounds can be super relaxing when you need to focus or get some sleep. And today’s
sponsor, Endel, creates personalized soundscapes to help you do just that.
Endel takes everything we know about sound and combines it with technology. Their app is able
to adapt in real-time to personal inputs like weather, location, and heart rate.
So if you’re looking to switch up your bedtime routine or to focus on your school work,
the first 100 people to click on our link in the description will get a one-week free trial.
Thank you so much for watching, and thanks again to Endel for sponsoring this episode.
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