IRA FLATOW: This is Science Friday. I’m Ira Flatow.

What happens in your brain when you see a familiar face? You know, you hear the door open. Your face lights up when in walks grandma, whom you recognize immediately. Scientists have wondered for years, how come your brain reacts so immediately to granny’s familiar face? Is there a so-called grandma cell in your brain that is programmed for immediate recognition?

Well, maybe not one neuron, but perhaps a whole bunch. Researchers recently reported in the journal Science that there may be a specific group of neural cells that are tuned to respond to the sight of familiar faces– at least, in monkeys.

So what does that tell us about how the brain is organized? Joining me now are two of the scientists working on that research, Dr. Sofia Landi, now a Schmidt Science Fellow at the University of Washington. Welcome to Science Friday.

SOFIA LANDI: Thank you so much for having us here.

IRA FLATOW: You’re welcome. And Dr. Winrich Freiwald, professor of neurosciences and behavior at Rockefeller University. Welcome to you, too.

WINRICH FREIWALD: Thank you so much.

IRA FLATOW: You’re welcome. So Dr. Landi, can you walk us through this discovery? You looked at how monkeys respond to images of faces, and then what?

SOFIA LANDI: Yes. So we examined an area in the brain that is the temporal pole, and it’s an area that is poorly understood, so we don’t know much about it. And it’s an area that is located right below your cheeks, more or less at the bottom of your brain. And we had identified this area before as one of two areas that might be involved in familiar face recognition in a study that we published a few years ago.

So we used, for this study, functional magnetic resonance imaging to scan the brains of monkeys while they were looking at images of faces in a screen, and these brain scans served us as a guide, so we can, in a way, zoom in and record the activity of single cells or neurons in the brain.

IRA FLATOW: Dr. Freiwald, would this area be the same kind of area that humans have?

WINRICH FREIWALD: We actually just got data on exactly that, and yes, we believe that there is the same area also in the human brain as the monkey brain.

IRA FLATOW: Tell us a bit more about that part of the brain.

WINRICH FREIWALD: As Sofia mentioned, it’s a mysterious part of the brain that we don’t know very much about, and it’s largely because it is very difficult to obtain any signals from. And we believe that is part of the reason why the question that you posed in your introduction– are there grandmother neurons? What happens in your brain when you see the face of someone you know very well– that this question has remained unanswered for decades.

So we now think that this region might be a very critical hub that is linking visual perception– the perception of a face– to memory and knowledge of people, and maybe even more broadly, to other familiar things as well. Within this larger brain region, there is the subregion that you also mentioned in your introduction that appears to be entirely specialized on faces, so linking the perception of a face to your memory or knowledge of people.

IRA FLATOW: But we see so many people that we know in real life that we would recognize immediately. That means there’s got to be a whole bunch of cells in there for all these different people. Does it not, Sofia?

SOFIA LANDI: Yes. So actually, what we found is that some of these cells are very specific to one individual, and other cells, they get activated when you look at pictures of, let’s say, all your friends, for example.

WINRICH FREIWALD: There is the sense, Ira, when you recognize someone, it’s not just in an automatic process or a thought process. It almost has an emotional quality to it. You mentioned when you recognize someone, or even anticipate seeing someone, that you might feel happy in anticipation or recognition. And so there there’s the sense of familiarity that you get. So we think that these neurons that respond to all familiar individuals might be eliciting this process, this feeling of familiarity.

IRA FLATOW: And could this process be happening not just with facial recognition? What about smells and sounds and things like that?

SOFIA LANDI: Yes, that’s actually also another good question. We looked into voices– for example, if voices could elicit a response in these neurons, and the answer was no. But we believe that nearby regions might be doing the same process with other stimuli that are not visual stimuli, such as voices, that would allow you to recognize someone in the same way.

IRA FLATOW: Why would the brain have this type of cell? What’s the reasoning? What’s the point?

SOFIA LANDI: Well, you know, we’re very social animals. All primates are. And we depend on others to survive, so our brains evolve in order to support that very basic social function of identifying who we see– how we react to different individuals. Once you identify who you are seeing, you will not react in the same way, if you see your grandmother or if you see a friend, right? So you have to adapt your behavior to who you encounter. It’s very important.

IRA FLATOW: We began talking about the theory that scientists have had about a grandma cell, and now we’re talking about grandma cells in plural. Do we know how many– approximately how many– cells it takes to make this recognition?

WINRICH FREIWALD: We would estimate maybe a million. It’s maybe more in humans. The initial idea, actually, was that there was going to be 18,000 cells. It was a made up story by an MIT professor at the end of the ’60s, Jerry Lettvin, but it soon became– was transformed into this idea, that there’s one cell and one cell only for every individual that you know very well. So there would be one cell for one of your grandmothers, a different cell for a different grandmother of yours.

What Sofia discovered is that there is a whole population for each individual that you know, and that the populations that are active for different people can actually overlap.

IRA FLATOW: That’s really interesting, because I’m wondering, do these cells store the memory of the face itself, or, as you say, interact with other parts of the brain– somehow check in with the memory part of the brain to accomplish that recognition task?

WINRICH FREIWALD: So we believe this is happening. We have not demonstrated this. We would love to demonstrate that.

What we were surprised by is that these cells are so specific to faces only. It is very clear that they form a link between the perception of a face and your knowledge of people in general, but this link is formed by these neurons only for the perception of the face– not the body, not the voice, nothing else that we tested. And to us, it was really surprising, why this mechanism would exist and would have this specificity.

IRA FLATOW: So Sofia, do we know what it is about the face that they’re keying in on that makes it specific to just recognizing the face?

SOFIA LANDI: So we know that these neurons like the inner part of the face, so they don’t care as much about the hairline, for example. And we also know that if you attach the face to, like, the whole body of the individual, these cells respond even in a stronger way.

That’s all we know now. This study is really like the starting point to answer a lot of the questions that you have, actually.

IRA FLATOW: I would imagine there’s a lot of questions you’d like to answer for this. I mean, one that comes to mind for me is, well, does it matter if the face is smiling or not?

WINRICH FREIWALD: Sofia actually tested this. We think that these cells are largely independent of expressions of emotions and that they are capable of responding to faces as seen from different viewpoints, as seen different distances, and with different facial expressions.

IRA FLATOW: Now, I understand from your research that the monkey neurons only responded to other monkeys that they had seen in real life, and when you show them pictures of those monkeys on the screen, only those monkeys they had seen in real life, they responded to. Would that be correct?

SOFIA LANDI: Yes, that is correct.

IRA FLATOW: But, you know, I’m asking, because for we humans, we’ve got famous people all over the place that we probably want to recognize, even though we haven’t met them personally. But we’ve seen them on TV or in movies. Might we perhaps respond a little bit differently because we’ve never met these people?

SOFIA LANDI: Yes, I think that that’s a very interesting question, and it also ties with a lot of studies that are done in patients. When some conditions need to be diagnosed, a lot of face name recognition tests that are widely used in, for example, Alzheimer’s research– they tend to use famous faces as proxies for familiar ones. So if what we see in monkeys is also true with humans, we might be missing some dysfunction of this area if we don’t use personally familiar faces in these tests. So something that we still need to study is how many times we must see a face, and in what context, before these fast responding temporal pole neurons are able to encode it. So this is one of the many questions that we yet have to answer.

IRA FLATOW: In other words, how familiar do you have to become with that face over and over again?

SOFIA LANDI: Exactly. Yes.

WINRICH FREIWALD: It’s very interesting to think about what it is that happens when we acquire familiarity with a person. Isn’t it that when we see the picture of a famous person that we have a bit of a sense of familiarity? So for us humans, it might be that, indeed, the face of a famous person might appear at least partially like that of a familiar person. Obviously, we’re not personally familiar with them, but it appears to us over exposure, reading about this person, and so on and so forth.

So one of the things we would like to figure out going forward is what actually is it exactly that is generating the sense in us and in our brain that we are familiar with another person.

IRA FLATOW: Could it be that it’s evoking a memory of our interaction with that person– either a nice, warm one, or one that’s not so nice? But we feel it in other parts of our brain?

WINRICH FREIWALD: That’s exactly what we think. But the interesting thing about famous people that we’ve never met is, how would that happen, if we never had a personal encounter with them? Yet to some extent they appear to be very similar to familiar people.

IRA FLATOW: Now, how do you apply this to people? Is it possible to directly measure this in people? I know in monkeys, you had to put electrodes in their heads. You really can’t do that with people, can you, Winrich?

WINRICH FREIWALD: We cannot. That is the reason why we are working with monkeys– the fact that they are similar to us and the fact that we can record activity in the brain. With fMRI, with brain imaging, we can answer the question, where is something happening in the brain? And we talked about the importance of that before because we had no idea what was happening in the brain, because we didn’t know where to look.

But after the brain imaging, we know where to look, and that is allowing us to figure out how things work– like what is really happening? What are the computations that are going on? That is not possible to do with brain imaging.

So we like to do both studies. We like to know what is happening in the human brain. We would like to illuminate the human condition. But this mechanistic studies require the monkey model.

IRA FLATOW: You know, smells– odors– evoke such strong emotions. Might you find also a separate area in the brain that might be devoted to odors and familiar smells?

WINRICH FREIWALD: Odors and familiar smells are probably a different process. They evoke such strong memories of your childhood and early experiences, and there are very strong links in all kinds of mammals– mice and humans alike– that mediate these processes. They likely use very different routes and very different mechanisms. This very specific similarity with individuals is something that requires a very high degree of sociality and of social intelligence– really being able to differentiate between individuals in a social group.

IRA FLATOW: This is Science Friday from WNYC Studios.

Sofia, I know that you’ve moved on from this project, but are you still studying memory?

SOFIA LANDI: Yes. I’m trying to, yes. I’m trying to study a different structure in the brain that is called the hippocampus that has been hypothesized to be involved in episodic memory. So for example, what you were describing about having an odor that elicits a very rich experience from your childhood– how does the brain enable a process like this?

IRA FLATOW: Dr. Freiwald, does this finding teach us anything about memory in general?

WINRICH FREIWALD: We think so. There is a very specific organization here, and we discovered this organization by focusing on faces, but we believe that it’s recapitulated for other socially important stimuli. We have an amazingly rich and amazingly sophisticated structure of social knowledge. We don’t just know individuals. We also know the relationships. And these are very sophisticated data structures, if you will, and we believe that they reside in the same brain region.

The second answer to your question would also be an answer to your earlier question about the organization of brain systems. We believe that this finding shows that there may be two different pathways of memories that we’ve not appreciated before– that there’s one pathway to form the memories and another pathway to retrieve them. The reason we believe that is that these cells are responding with astonishing speed. We had imagined that it would take them longer to respond– longer to respond than cells we discovered before, that respond to all kinds of faces, familiar and unfamiliar ones alike.

But it turns out that these cells that respond specifically to familiar individuals are responding just as fast as the other cells, so they must be activated by a separate pathway that we don’t know yet.

IRA FLATOW: Sure, because when somebody walks into a room, it’s a surprise, and you immediately recognize them, don’t you?

WINRICH FREIWALD: Exactly. So maybe we should have expected this, but we did not.

IRA FLATOW: Doesn’t all this sort of tell us that we really don’t know how much about the brain as we think we do? I mean, it just seems so fascinating. Something as common as this is just being discovered.

WINRICH FREIWALD: I think if you’re in neuroscience– and I don’t know, Sofia, if this is your sense as well– I’ve been around now for some 30 years, and in our line of work. I think we do appreciate how much we don’t know yet.

On the one side, we know a lot. There’s a gazillion facts. There’s so much published all the time that it’s impossible for anyone to keep track of everything that’s discovered, and there’s probably no other organ in the body that we have a similar amount of knowledge amassed over time as we have for the brain. Yet to explain especially cognitive phenomena, the question to answer, like, what makes us intelligent? I think we do appreciate that there’s a lot that we still don’t know.

IRA FLATOW: Fascinating. Thank you both. We’ve run out of time. Dr. Sofia Landi, Schmidt Science Fellow at the University of Washington, and Dr. Winrich Freiwald, professor of neurosciences and behavior at Rockefeller University. Thanks again for talking with us today.

SOFIA LANDI: Thank you for having us.

WINRICH FREIWALD: Thank you so much.

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