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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, but neuroscientists have been trying to understand exactly how our brains do this for years.

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This episode is sponsored by Endel, an app that  creates personalized soundscapes to help you   focus, relax and sleep.

The first 100 people to  click our description link will get a one-week free trial. [♪INTRO]. 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. [♪OUTRO].