에피소드 46: Dr. Sergio Pellis

that he shot in his backyard in Melbourne, Australia and showed me the film and what I saw was a pair of Australian magpies engaging in rough and tumble play, just like two puppies. I'm using puppies for your benefit. So they're rolling around, grabbing one another and I looked at it and I said, I asked my supervisor, why are they doing that? This is 1975. I said, why are they doing that? And he said, nobody knows. And I thought, well, this is perfect. For four years PhD, I can solve the problem of why animals are playing. So fast forward to 2024, I'm still working on play and as you mentioned, I've got a large body of work now and slowly trying to tease out the big question I started with, haven't solved the big question of why do animals play. But as the conversation here will progress, I think you'll see we've got better and better ideas and snippets of understanding of the phenomenon. So that's how it started. And that's why it's taken me 50 years to do this. This is, it just fascinates me. Wow, where do we start? So we know that all, like there is a special thing about mammals in particular. Like we have this special, like it's baked. Like it's not play like in the last, whatever, 20 years or so. I think it's, you know, we didn't think, but we finally realized that play is an innate, it's just a primary reinforcer. It's not something that we have to, like it's a fundamental basic need for development, as you said. That was one of the kind of unexpected even things that came out in, I don't know how long ago that was. But we realized that mammals are just extremely playful. And especially like humans, we can, I mean, there is an infinite number of games we can come up with any time we decide to. And the thing with the dogs, it's, I think, my speculation of how, like people always, you know, the theories about how dogs and humans came together. And, you know, the scavenger theory and so on. But I think play had something to do with it. That's just my gut feeling that there was somewhere, even if it was a bone, but there was some play involved simply because humans and dogs are, we, like most mammals as we know, they kind of, you know, in the development, and in the younger stages, they are very playful. But that kind of fades off as they grow up to where humans and dogs. And I'm very curious to hear about your take on that. But we play until we die. And, I mean, as soon as all needs are met, we want to play, right? And it's just an amazing thing. And, of course, that question, why do we play, just cannot help it. But it comes as a first question, which is, it's a very interesting one.

And I am dying to hear your take on that. Yeah, so if I can break down what you've just said into different sub-questions, right, we'll get a better handle on what the diversity and the range of phenomena that we call play are. So the first thing is, yes, mammals are amongst the most playful group of animals on the planet. But even amongst mammals, not every species play. So one of the first questions is, why do some animals, some species play and others do not, right? And if you look at how this evolved, it seems pretty clear that the ancestral state is for a non-playful ancestor. And then from there we spawn lineages that become, that have lots of playful species, some that do not ever show play in some species. So the first question is, how do we go from non-play to play? And then the second question is, well, what are the conditions that make the more playful members of the mammalian family playful? What's enabled them to develop this exaggerated play, which, as you said, in some species is quite remarkable, like humans, dogs, chimpanzees, whatever. And then the third question is, okay, so you do all this play. So in some species, so what does it buy you? What are you getting out of it? Is it just a way to fill up spare time? Or is there some added value to the engagement and performance of the behavior? Yeah. So if we sort of break up the big question into these smaller questions, we have a better chance of getting some understanding. And as we progress through this discussion, what I think I'll show you is that some of these questions, we're starting to get some really good insights into what the answers may be. Some questions, they're still a big mystery, and it'll probably be in somebody else's lifetime, if ever, that they're answered. Which is cool to have that part too, right? Oh, yeah. Well, I've had some pretty good graduate students that I've trained. So for them to know that there's still some really big questions to answer makes it encouraging for them to go forward with a career rather than go, okay, well, I know everything, so I might as well go and do something else. So if we start with the first question is, where does play come from, right? What are the origins of play? This is probably still the most vaguely understood question, and we're getting some ideas of what some of the components of an answer will be, but it's still pretty premature. But here's a stab at my best guess as to what constitutes an answer to this. If you think of animals doing stuff, so let's think of, I'll give you an example.

Lions in the wild, they have to hunt other animals in order to eat, okay? Now, various studies over the last 60 plus years have shown that in the wild, lions are successful in hunting in maybe one out of 26 attempts, okay? So now let's think about the way we normally think about people and other animals being rewarded for behaving in a certain way. So as a dog trainer, you know, you reward your dogs to do certain things you want them to do. But if you didn't reward your dog for after 26 times it did this behavior, it probably would not make the connection. The reinforcements is not there. Yes. So the question is, well, what makes a lion wake up against the next morning and go hunt again, even though it wasn't rewarded by a meal after the last hunt, the hunt before, the hunt before, right? So one way to think about how behavior is organized is that one of the things that needs to happen is that for essential behaviors, behaviors you cannot afford not to do, they have to be self-rewarding. So they're just getting up and the excitement of going out hunting is enough to reward the lion to go out and hunt again, right? And they're very much rewarded by a steak dinner. Right. Right. They're innate. They're just baked into your DNA. It's not like you're... Yeah. Yeah. So doing the behavior becomes rewarding in and of itself. And I think that's a fundamental feature of what has in some lineages led to the evolution of plague. So if we now take that seed and go into, okay, now why do some species exaggerate this innate desire to perform behavior to such a degree that we as observers recognize it as, well, it looks playful. It's different. It's play. It's no longer just hunting behavior. It's play. All right. So I think the next step is you look at lineages where there are things like spare time. So there's extra resources available. The animal has the capacity to become bored. So a little bit bigger brain, a little bit more cognitive capability. So you create conditions. Let's add another one where if you go out and do some random playful activity, your chances of being eaten by a predator are low. So in lineages where these conditions are created leads to the opportunity to exaggerate that innate propensity to engage in behavior because the behavior is self-rewarding, to transform it into a more playful form of enactment, which is why a lot of play in most animals is built on those innate survival-based behaviors. Like anti-predator behavior. Like anti-predator behavior, predation, social aggression, sex, et cetera. Right? Yes. Yes. Yes.

Only a few animals like humans have gone to the point of creating novel types of play that we refer to as games that are really divorced from those survival things. So we have a gradation. So we have a gradation. Okay? Then, once you fill up your time and using up excess resources to engage in play, if that play now has some feedback on how you develop, how you organize your behavior in a positive way, the natural selection would foster that. And so we have, in some lineages, where the play has not only arisen, but now fulfills an essential function. Yeah. And we see that in, certainly in humans, we see it in many primates, and we've demonstrated in, even in rats, that the playing ends up providing feedback to developing parts of the cognitive architecture of the brain to be able to perform better in a variety of different situations later in life. Yes. Right? Yes. Yes. Yes. So we go through these gradations. So that means when you ask, why do animals play, and you immediately think of, well, everybody must benefit. Well, that doesn't explain why it doesn't benefit everybody and why not everybody plays. So you have to take this graded step. And when we get the dogs, to people, to monkeys, to rats, we have the full circle. We have the function, we have the performance, and we have the opportunity. There is the standing question or assumption that, okay, play, one of the benefits is, okay, the youngsters, they immediately start to practice skills, right? Or the other option, and I've heard you say this as well, that I also feel more inclined to go along with, is that, I mean, there's like so many benefits of play, but especially in the developing, the young age, it's almost like making those brain connections and kind of putting the body and the brain to work together and understanding who you are and what you can do in some way. But not necessarily that it's, okay, I'm doing this for that practice. I think that comes later on as a skill, very useful, but the initial benefits of play is just to really put brain and body together of who you are and what you can do. Can you really jump this high or can you, what do you think? Yeah, so I agree. So for about 100 plus years, the predominant functional explanation of play is that it affords young animals an opportunity to practice skills. To practice skills, right, right, right. Okay. And from, from when I first started studying play in the 70s, there were a series of papers on cats, on coyotes, on a variety of animals that tried to test that hypothesis. And it kept on coming up negative, like playing doesn't make you better at predation.

It doesn't make you better at fighting, right. And so that hypothesis ended up becoming weaker and weaker, but still it was the most useful one to get a simple explanation. So even in documentaries to this day, it's still the most commonly reported explanation for why animals play, right. Even though it's just simply the evidence is not there. Now, what has been shown, and we've shown it in rats, other people have shown it in hamsters. There's some indirect evidence from humans and from a few primate species showing that, well, the play is actually changing, is doing what you just suggested before. What it's doing is allowing the animal to really understand what it's capable of and what it needs to do with that capability to modify it in different situations. Right. And so adapt their behavior to context in a much more effective manner. Right. And so what we found and been corroborated in a couple of other labs now is that playing, and it doesn't matter what kind of play it is, it can be aggressive play, sexual play, predatory play, ends up influencing the development of the, in mammals, the prefrontal cortex, which essentially is a place where you gather all the information from all the rest of your brain, from the rest of the situation you're in and tries to figure out what should I do. And let me just give you a really simple component of that process that I think everybody in the audience will understand. And that is, if you go to work and your boss says something insulting to you, your first inclination is to react. But what you need to do is stop for a few seconds, think about how do I really want to react? Because I can escalate the situation, I can de-escalate it. So impulse control. Impulse control. Right. It's an essential part of life. And certainly for social animals, if you have no impulse control, there's a real problem. And I don't know, where are you at? New York? No, we are in Florida. We are near Tampa. Yeah. Okay. So some of your audience may remember the show Seinfeld. And Kramer is an excellent example of someone with no impulse control. Short feels. He says what he thinks. Yes. Right? That gets him in trouble all the time. And again, that is one of the skills we need to be able to organize our behavioral responses in a more effective way. And that's going to be true whether you're a rat or monkey or dog encountering another dog and you have to make a decision as to whether to escalate this to aggression or not. You encounter someone and you're trying to convince them to have sex with you.

You're encountering prey and deciding whether I should lunge now or swing around and come at a different angle. Right. All the strategies. Yes. All the strategies in life, basically. Exactly. And so I think where play has had a feedback effect on skill development, that's these higher order skills of piecing together how to adapt your behavioral repertoire to this specific situation most effectively. So if nothing else, if everybody goes away thinking, okay, play improves impulse control, and that's been demonstrated multiple times in the laboratory in the Netherlands, then you've got the picture. Very cool. Very cool. Yeah. Like I think always something like, you know, because I'm, I mean, by my accent, you would guess I'm not born in the States. I'm originally from Bulgaria and we used to play, I mean, soccer, football was like the game, of course, in Europe. And, and always a lot of my examples always connect either with martial arts or with soccer. And, you know, like when you give a ball to a kid and they start to kick it, of course, they learn how to play with the ball. But they really, what's happening is they learn about what they can do and how to get better doing it. Right. And there is so many, like, I, I don't know if, I mean, I'm sure you probably can list all the benefits. I, I always try to think of how much, how deep it goes. Because like, of course we have the, the cooperation because we, you know, to play, somebody has to want to play with you. Right. So that's like a, just as the impulse control, cooperation is of extreme value to learn how to cooperate with somebody, even if it's stronger or weaker, because the game's going to end if you don't cooperate. Right. One way or another. Right. And the other big one to me, I mean, besides all the social skills, but, but the fact of, you know, like, like kind of finding out who you are, who is who in that social group. I think through play is a, a, a very healthy, safe way to figure things out. No. Yeah. So, so that takes us to a fourth question, which is, which is that so far it looks like from the comparative evidence that about 50% of mammalian species that play as juveniles continue to play as adults. And so now you have, well, it can't, adults can't be using play to, to help foster the development of these prefrontal skills because they're already there. So why do, why do half the species that play continue playing as adults? And certainly for social play, one of the answers are exactly where you were alluding to, that the play is used as a way of negotiating relationships. Right.

Because if I, if I engage you in play and you're either UI become a little bit too rough or too, whatever the game is. Right. Then you go, depending on the reaction of the other person, you can say, oh, sorry, I was just playing. And you, and you've got a way of gracefully backing down. However, if you encounter one another and you immediately go to, okay, the choices between fighting or not fighting, then it becomes difficult to have a way of backing down. Go on, snap. So the play has been demonstrated in humans as well to function as both a graceful way of sampling and identifying where you stand in the social hierarchy in the group. Which is super critical for social species. I mean, it's absolutely. Without knowing where you stand, it's a chaos. It's dangerous for everybody, right? And the same applies for sexual encounters, identifying mates. You can have a little bit of playful banter. And then if it doesn't work out well, you've got a way of backing away. If it works well, you can escalate it to more intimate sexual behavior. But again, it's a way of getting your bearings in a social situation and understanding what the dynamics are with the other individual or individuals involved. And so you can know what to do next. So in terms of the comparative literature, what's known is that there are some species which are super hierarchical. I'll just mention a couple of primate species. There are Japanese snow monkeys, super hierarchical, right? They have little to no play in adulthood, simply because everybody knows what their status is in the group. So depending on who does what to whom, you know what you're supposed to do. There are other related monkeys, particularly ones from the Sulawesi Islands, that are also hierarchical, but the hierarchy is much more fluid. So even though you're dominant to me, and most times you can come towards me and take whatever I'm eating and you can get away with it because you're dominant. But in some of these Sulawesi monkeys, sometimes the subordinate will go, well, you've done this once too many times. So I'm going to turn around and bite you, right? So now you as the dominant have to figure out, you know, what's my standing with this particular person before I push my luck further? And so what we have is in these Sulawesi monkeys, a lot of adult-adult play, which seems to be used to navigate and negotiate and reinforce where they are in the hierarchy. Whereas in the Japanese macaques, you don't have to worry about that.

There's no need, because once you're in that particular position, you know exactly what you can and can't do with another animal. So again, and in humans, obviously, particularly in more democratic, quasi-egalitarian societies like Canada and America and so on, you know, it's not always clear exactly where you stand. So some more playful ways of interacting are more useful than in other societies where the hierarchy is very rigidly maintained. Everybody knows what they're supposed to do with everybody. Here is a question. Why is it that a big, big percentage, big portion of play has some element of aggression? It's not aggression, but it's aggression in some way. It's like we're playing, but the team is aggression. You know what I'm saying, right? Like in a law, is it just predators or is it like I, from my experience and observations and what I've learned, it's actually, it doesn't have to be a predator. They all play in a somewhat play aggression, if that's even a way to explain it. Yeah, absolutely. So it's not limited to predators. It's true for at least for all species that engage in rough and tumble play, right? And it's true for rats, which are non-predatory species. It's true for macaques, monkeys that are non-predatory. It's true for dogs, which are predatory. It's true for cats, et cetera. So I think what's going on, and the evidence is really starting to push in this direction, that there are two components to this. First, rough and tumble play, to be fun, to be enjoyable, has to be competitive. Yes. Right? And again, everybody can think of themselves back when they were very young and yet you're playing with someone that you always win. That's not much fun, right? There's got to be a challenge. Similarly, the reverse is also true. If the other person that you're playing with is always winning, you won't find it fun either, right? So there's got to be a balance. And so when you look at rough and tumble play in a variety of animals, which we have, what you find is that there's an element of both competition and cooperation. And part of the balancing act that you have to decide when you're playing with a particular individual is, okay, I'm stronger, more skilled than the other person. I've been winning a lot, but I can feel by the tension in the other animal's body and so on, by their mood, that they're losing interest and they're no longer enjoying this. So in order to engage them further in play, now I have to exaggerate some cooperative element in my behavior to make it easy, facilitate them getting at least an occasional win. All right?

And it seems that certainly for the development of social skills that play can influence, it is that balance. And so we've done experiments where we've exaggerated the lack of symmetry. So it's very asymmetrical in favor of this animal. Even though this animal is playing a lot, it's not getting the benefits from this brain development. And it's when the two are more closely matched so that they're both seesawing and winning and losing that you get the maximum brain development benefit. And I think then in adulthood, we're talking about negotiating relationships. It's that using that relative balance between competition and cooperation that you're using as a judgment to know, okay, with this person, you know, I can win 60% of the time. And that person is fine only winning 40%. This other person, I have to alter my behavior because they get really annoyed if I win more than 70% of the time. So again, you're using play as a way of adjusting where the correct balance is between cooperation and competition to maintain relationships or in childhood to develop these social skills. Yeah. Yeah. Yeah. That's like I mentioned to you in our correspondence that I have a school for dog trainers. And one of the things when we talk about play, which we do extensively, I always give example. One of my favorite examples is like imagine that you have like some of the best basketball professional league team and the coach comes and talks to us here and say, hey, you guys want to play? Of course, we're going to say yes. How can we not? Even though we know the outcome. But I mean, this is a once in a lifetime opportunity, right? So of course we will play. But then once it's done and the next Sunday the coach says, hey, you guys want to play? We would say no. We would rather have a front seat and watch them play. And the same for the top players because why would they want to play with us? We know the outcome and they know the outcome. And as soon as we know the outcome, the game of the competition is not there anymore, right? And so that kind of ends it in that way. But the interesting thing about play is also, you know, having that freedom, like the best play when you have this, when it's self-directed, like you have to figure it out as you're doing it. The benefit of the play is like you have to have the control, which goes all into the cooperation, right? But it's this exploration of how to navigate. So it is competitive, but there are some rules. We agree on how to stay in the play because the play can become very fragile very quickly.

And having that innate ability, which it's amazing, that desire to, okay, we're going to play and we're going to find out what we're going to play. And there's going to be some rocky ways, but even the rocky moments of the play are of extreme value because those are the moments where you actually learn the impulse control, learn the cooperation. Like once we know how to play the game, then it's cool to play the game. But learning the game itself, it's the most value of the whole experience, no? Yeah, yeah. Yeah, and I think to reinforce that point, we see that in non-social play as well, where animals are playing with objects or just moving around, like you said, you know, jumping from one branch to another for a monkey. What they do is it seems that as they're getting better, they add a little bit extra challenge, right? So it's pushing themselves to the limit. And in some exaggerated cases, you can see this and it's been labeled self-handicapping, where you actually make it harder for yourself to succeed. And so you have to overcome that challenge. And in social play, the other animal is providing the challenges for you. But in solo play, well, you have to be the one introducing that challenge to become really stuck. Why the hell are they doing that? Yes. And it's probably because of that very thing, that what makes the play fun is to push yourself out of your zone of comfort. This is like two guys playing tennis and the one is clearly on a different level and decides to switch hands to make the game balanced, right? Yeah. Yeah. Yeah. Yeah, exactly. Exactly. So when you mentioned, so, gosh, so many questions. We have the, how you say, the rough and tumble. We have the games where it's really interaction without any objects. And then we have the ones with objects. It's very interesting to me how much, if any, play with mice and rats goes. Do they ever pick an object and chase each other? Kind of like how dogs would do or other, or they are strictly interacting in a physical way directly. Yeah. Yeah. I've never seen that object competition in rats. But rats are, they tend to, I mean, they are pretty, they can be quite aggressive for just in the colony and everything, right? With each other. And they resolve that. Some of that gets resolved through some form of play. That, right? Mm-hmm. To where, like, with dogs or humans, we can resolve it by playing, again, basketball. Or the dog can grab a little branch and the other one can try to steal it. And then they can establish that way without the actual, all the dogs also are masters in playing without any objects.

And just really go at their necks as, you know, as we say, they are practicing skills, right? But it's a dominance. It's a, when the two, especially if it's two, when it gets three or four, the dynamics kind of change. And that will be another conversation that I want to have with you with, do the rats and mice play in groups like that? Because the dogs do. But typically, especially when dogs play one-on-one, often you will see them in the dog park and people are like, oh, they are playing. They are having fun. And clearly, the one is having the time of its life and the other one is just kind of trying to dodge and defend. Because if he doesn't or she doesn't, then he gets to be bullied, right? And so with the mice and the rats, are they, do they prefer to play one-on-one or do they do some group also like play? Do they team up or? No, yeah, no, there's no teaming up. So, in fact, the vast majority of species that engage in rough and tumble play, the play is predominantly dyadic, right? So, in a group, if you have a cage with a group of rats and they're playing, what you'll have is an individual play with this one. Then they'll break up and they'll go play with someone else. So, it's basically serial dyadic interactions, right? And that's true for most animals. It's very rare that a third or fourth animal joins in and they actually create a novel way of interacting in that group structure. Right. That's uncommon. They can end up being on the way. In some cases, yeah. So, often where you get a third animal joining in, and we've seen this in rats and we've seen it in otters and Japanese monkeys, is the one that joins in will attack the one that has a disadvantage at the time, right? So, it's taking advantage of one of the other ones' disadvantage. But there are exceptions. And the two most striking ones that I know of, one we studied ourselves, which was one of the Solowese monkeys, relative to the Japanese macaque, and bonobos, relative to the chimpanzee. And where you can get in both bonobos and the Solowese monkeys is most of the play is dyadic, but 30% to 40% is non-dyadic. So, you have a third one joining and then the three are competing with one another. Then a fourth one joins in and then the four are competing against one another simultaneously. But it gets to a point where, when, but, okay, let me back up. So, if you're one of these monkeys, what you're trying to do during rough and tumble play is to bite the other person on the upper arm shoulder here, right? So, you try to grab a bite. Now, two animals doing that, you can see how that can work. Add a third animal.

Becomes chaotic. It becomes more complex. Yes. The fourth animal becomes even more complex. And what happens is, as the complexity increases, the thing breaks down. And what you can end up having is, as many juveniles as there are in the group, and one group of Tonkin vacacs that we studied, there were eight juveniles. And eventually, all eight just piled on top of one another. And then they stopped bothering going for the shoulder. They just grabbed someone's hand, bite a hand. Somebody else grabbed a foot, bite a foot. So, they broke the theme of the rules-based dyadic encounter. So, instead of trying to maintain the dyadic rules, but with a third or fourth animal, it just completely broke down into anarchy. Right? For Japanese macaque, that would be a terrible thing to happen. Because they wouldn't know how they could be behaving. How to get out. Yes. So, it would be totally unpleasant for Japanese macaque. But for bonobos and Tonkin macaques, this is perfectly acceptable and fun. So, seeking somebody that matches you the way you want to play. And typically, when we dox, and I think with people, if we find out, we very quickly find out if it's worth to play with somebody or not. And often, we may not be able to get out of it. It can lead into some fight. But we very quickly gouge what my skill against how they, how we line up. And what is, to me, interesting, and it's always been in my head, and it's a big, I wouldn't say it's a problem, but there is a, in dog world, there is a very much of a controversy as far as like, you know, there is that notion that all dog training should be done through positive reinforcement. And there should be no discomfort, no aversive, no fear. But then when you look at play, it's clearly about some discomfort. In fact, it's probably the most interesting play. He has some elements of aversive and avoiding, and if you cannot avoid it, you kind of get punished for it. And those are the ultimate skills. And there is some, something that kind of sucks you, that you like that kind of game, that you want to explore that discomfort, right? Yeah, no, I agree. I think that's exactly right. And I think that's one of the key features of play is that, as we talked about before, you're adding some discomfort, either psychological or physical, to make the situation more challenging, more interesting to work your way through. And I think if you try to completely eliminate all discomfort, the animals actually will not enjoy doing the behaviour anymore. Right, right, right, right. And to me, that's even more aversive and more punishing to the animal.

Yeah, and that's especially with dogs. Like if you imagine, you know, going to the shelter or going to a breeder and getting an eight-week-old puppy, and they don't get that experience of that type of play simply because it comes from a good place in our heart not to, you know, not to experience fear, not to experience discomfort. But there is a, how do I say, like a healthy dose of it that it's really needed. And it's, in some ways, it's almost, I compare it, I'm old enough that I can say I grew up on the street, which kind of sounds crazy. But we went to school, and then we played on the street all day long or all night long. And we learned how to do all these things that we're talking about. And there was, there was the, you know, the little conflict, the little corporations, the little discomfort. And at this point, this is, I think it's difficult for kids missing that side of, that type of play. Like parents think, okay, we're going to take the kid to do a karate. But it's all structured to where they don't, they don't get that self-directed and exploration of what they, it's all very, and with puppies, it's very much the same. Like we have, like you go to the pet stores, and you can have the brain toys to where they can use their nose, and they can figure things. Like there is a lot of cool things. But missing out on that type of play where there is that little bit of a question mark, well, who's going to win here, and how is it going to really hurt this time? And it's such an important part of development, right? Yeah. Yeah. And also, you know, think of, if you're engaging in play, most of the time, the effective state is positive. Like you're doing it because you're enjoying it, right? Right? And particularly in rough and tumble play, you know, and I can see this in my rat sometimes, they lunge up at one another high in the air, and one gets turned over and bang, and you can hear the thud as it lands on the ground, right? And you go, nope, that's got to hurt. But the rat will take that in its stride and bounce back and attack the other one, right? If that happened in an aggressive encounter, the same level of pain would alert the one that's experienced the pain to either completely submit or to escalate the aggression. Right. And so in play, you could experience similar levels of pain, but what you're doing is you're weighing that pain relative to what goals you're trying to achieve in that situation. Right. And so I think play becomes an important place to learn that, hey, to get what I want, sometimes I've got to experience some pain,

but it's not pain that I would treat as aversive, whereas the same level of pain in another non-playful situation would lead you to a very different end point. Yes. So, yeah, I think some physical and psychological pain is built in to play, and the more we try to sanitize the play experience to avoid any psychological or physical pain, we're actually depriving the kids involved, in particular the kids, the opportunity to gain the most important, valuable lessons they can from childhood. And so we're not doing them a favor, right? Which you're obligated to learn how to cooperate in these specific situations, right? Yeah. Yeah. Yeah. And again, because we're very social, we want to interact. We like playing with other people. And so you go, now, if I'm inflicting too much psychological or physical pain on my partners, and they stop playing with me, right? Well, that makes me unhappy. So it forces me to rethink, oh, man, I want to get back into the game. What do I need to do in order to make the other ones accept me again? So you're learning valuable lessons about how the world works and the kinds of skills you need in order to be able to gain what you wish to gain out of the world. I have another interesting one that I want to ask you about. And like what I call it, like this is just something that I don't know, I'm sure you will come up, you will say the right definition of it. But I call it a home base as far as like somebody's character, somebody's temperament to where like, you know, you like, let's say you're an ATM machine and somebody taps you on the shoulder. And some person will just come and punch the other one, somebody will freeze, like there will be these responses that they, no matter if you are like black belt in some martial arts, in that particular situation, you totally can respond by freezing and not being able to do anything or do the wrong thing. And that kind of home base character difference, like, because that also, that matchmaking, if I want to say it that way, can, no matter how much you want to cooperate, it's just, it's not a good match. And it either has to, we have to split or we end up in a, in a much more confrontation, right? Just because of the personalities that the two meet. Is that something real? Yeah, I think it is. And I'll give you an illustration with, with, with our rats. So what we initially discovered was that engaging in interactions, playful interactions as a, as a young rat, a juvenile rat, leads to changes in social skills and a change in a particular area of, of the prefrontal cortex called the medial prefrontal cortex.

So I'll just say MPFC. Okay. And what we also did was say, well, if that's good, what, what if we give rats an opportunity to grow up with lots of other play partners? So there's multiple animals, right? And what we found is, well, in this case, we're changing another part of the prefrontal cortex called the orbital frontal cortex or the OFC. So think of orbital frontal as the part that's sitting above your eyes and the medial is right down the middle here. Okay. So these two different things, and then we did experiments to show that the two are differentiated. One based on play experience, the MPFC, and one based on how many individuals you had to interact with. So diversity of partners. Then we discovered that the play induced changes to the MPFC are stable throughout the lifetime of the rat. So once they change in the juvenile period, they remain the same throughout life. And you think, well, what does, what does that part of the skillset do for you? What it does is it says, if you throw a punch at me, I should duck. Right. And that doesn't change throughout my life. Right. It's not that I want to be hit in the face when I'm 10 or when I'm 70. Right. I just don't want to be hit in the face. So that's a skill. And so timing and really what it, what this area of the brain is important for is time is helping you time this correctly. So you don't want to go too soon or too late. Right. You've got to judge it just right. So that's one of the things you're learning with the play experience. However, the changes in the OFC. If you continue leaving the animals in the same stable group of partners, eventually the OFC changes back to the way it was. So it's it's re altered back. But then if you expose those animals to new partners, the OFC changes again. Right. And so what did we discover the OFC to do? It's it does. It's not necessary to use the OFC to decide whether to duck or not. But. Who the who the other animal is and one of the important features in the other animals is whether they're dominant to you or subordinate. Right. So, you know, well, if it's dominant, I should do this. If it's subordinate, I can do that. Right. So I'm adjusting my behavior according to the identity of the other animal. And I think in that regard, what we can see is that there are some skills that are developed in childhood through the experience of play that last for your entire lifetime. But there are other skills that need to be updated, such as the OFC, because over time you end up having to interact with new characters. Right. Right. Right. Right. You can tell from my accent, I come from Australia.

I've spent time in Florida. I've spent time in Illinois. I've spent time in Tel Aviv. I've spent a lot of time in Canada. And so I've had to go from different workplaces many times. And you have to learn to cope with a new cast of partners. Right. And each time you have to adjust your behavior accordingly to the individual personalities within your social group. So, yes, I think there's a role for both. Right. That you have some stable skills that are going to be useful to you forever. But there are some skills that need updating all the time. Which is where we go, where we talk about the brain making, the prediction errors. Right. Because the brain has to, the most important thing is to be able to predict. But sometimes it's wrong. And then it has to adjust and save a different file in the folder. Yeah. Well, in my time at Lethbridge, I've been here for 34 years now. So I've seen many, many deans come and go. And, you know, you learn, okay, you know, the certain rules of etiquette that you have to engage in when you're dealing with your superior. But there's different personalities on how they, what kinds of ways you can raise issues and challenge that person. Right. And so you spend five years with a particular dean. You understand his or her personality and you act appropriately. And you've got a way of working out, you know, where can I get what I want and where do I have to give in, et cetera. But then a new dean comes and it takes a couple of years to go, oh, man, I can't use the same strategies I used as the previous dean because this doesn't work. It's a different personality. Very true. Very true. Talk to me a little bit about the deprivation from play. Like there is quite a few different, like we know it's extremely valuable. It's extremely important, especially in the, like the young, any animal or any mammal. I've read somewhere that if a rat even doesn't get touched, they end up like dying or something really. Like if they never get the interaction that is totally isolated, they just don't even make it through life. Is that a thing or is that something that I? Yeah, it's sort of true. But there's some nuance. So if you go through life and again, we'll deal with rats because they've been the ones most intensively studied on this. So your first three weeks of life, you're very dependent on your mother. So the first week to two weeks, you're totally dependent on the mother to feed you, to keep you warm. She needs to link your anogenital area in order for you to be induced to urinate and defecate. So just like a cat in early stages in a dog's life. Right.

But then in the third week, you're starting to explore eating solid foods on your own. So you become gradually less dependent on her for the food. You also are growing fur, so you're starting to be able to thermoregulate by yourself a little bit more effectively. But essentially, the first three weeks are really critically dependent on your interaction with the mother. Then after you're weaned, so you're no longer using the mother for food, you can eat by yourself. Then comes the juvenile period and they're where your most frequent interactions are with other juveniles of the same age. And a lot of the time when you're interacting with each other, you're doing a lot of play together. Right. So particularly that first week extending into the second week, how much the mother licks you, picks you up, physically touches you, impacts the development of another area of the brain called the hippocampus. And also it changes your stress response levels. Right. So what happens to these rats, if they're denied that maternal care and interaction and touch, as they get older, their stress response always remains at a higher level. And that stress response has a negative effect on the hippocampus. And hippocampus is very important for memory and learning. Right. So you end up degenerating and very quickly lead to an early death. Right. So maternal touch in that early phase is really critical for certain things. And then in the juvenile period, peer-to-peer contact, because most of the rough and tumble play involves actual physical contact with one another. Right. It provides an important avenue for further refining your stress response, your pain thresholds, and all those things that, again, will later affect how your stress reactivity is engaged in various situations and so can affect your life. So if you now have had poor physical contact with your mom early in life, you've had poor physical contact with peers in that early juvenile period, you now as an adult have more greater difficulty in regulating your stress response. Right. Because you're lacking the skills to interact. Right. You're lacking the skills to interact. And then the brain becomes, it's very tasking. And then it's like this neuro, it's just a neurotic crisis, basically. Right. So you have these negative effects on the brain. But also, if your stress response tends to remain high for longer periods, one of the things that happens when you have a stress response, which, of course, you need to do, is one of the things that shut down is your immune system. Right. Which is fine in the short term.

If you're trying to avoid being eaten by a lion, you're not going to worry about getting sick two years from now. You're trying to avoid getting eaten by a lion now. So suppressing your immune system is not a problem. The problem is, if the stress is chronic, and so your immune system is lower in a chronic way, now you're more susceptible to ulcers, to tumors, to aterosclerosis. And that's been shown in rats. So rats that haven't had this physical contact with the mom or the kid or the peers will end up dying, have shorter lives because they end up with all kinds of diseases that they can't control. Can they make up in time for the lack of that playfulness in the early age? Yeah, it seems that some things are hard to recuperate from. So some of these negative effects, you're not going to be able to compensate for later in life. So it is critical. I mean, it is. Yeah. It really is. What about like when we are talking rice and mice? Mice, I cannot help but ask about the spinning wheel. Why is that fascination to where like, even I've read a study, I think it was in Holland. I'm sure you know of it, that they actually put wheels like out in the outdoors and eventually they were going and spinning in them. Right. What is the, I mean, how much there is playfulness? What is going on? So that goes back to the very first question that I broke down your big question to, that animals are engaging in behaviours self-reinforcing. And what that reflects is that I just like running or walking. And so you provide an opportunity to do that and they will do it. Now, in the wild, yeah, they'll do some, but obviously in captivity where they're not doing anything else except being in a cage and getting fed. So they'll do it even more. So that's the problem. And let me give you an example of how this relates to the natural history of the animals concerned. One of the most difficult mammals or terrestrial mammals to keep in captivity are polar bears. And one of the reasons for this is they have part of their lifestyle is to walk enormous distances on a daily basis to find seals and other things that they're going to eat. So walking is really part of what they need to do. And so when you put them in a cage and you can never replicate the wild in a zoo cage for a polar bear, they end up very quickly developing those stereotypes where they walk back and forth, back and forth. Right. And that's simply because innately they're built to want to walk. And so that means they are positively reinforced by walking.

And unfortunately, that's very interesting because like I know I haven't been to a zoo for quite some time, but back in the day, the zoos weren't even as cool as they are today. So you would see mostly what you just described, that pacing. And I don't think, as you said, it's kind of a need and a displacement, but they don't necessarily get the benefits of it. It's a very neurotic thing to where the wheel most likely, just like anything that a human would go to the gym and get their body working, and then get all the endorphins and all the basically the brain is like, wow, the body feels good. Therefore, we feel good. Right. And probably that kind of physical activity, it's a feel good. That is most likely the self-reinforcing reason. Yeah. Yeah. If you, like, you know, I'm sure this is a little bit of a kind of sidestepping question, but because I'm sure you have something to say about it, way back in the day, like when we would put the two rats in a small box and we would put the electricity and they would get in a fight, we'll stop, they do all, so on. When that kind of induced aggression, how is that happens, would it happen when they have space and when the electricity is actually contingent, when they can make sense? Because it seems like from those experiments, they had not, they were just like, okay, something really bad is happening and you're right in front of me and I don't know why and we go into a fight. Like, and that's why they call it induced aggression, right? But I'm very interested in this kind of studies. Like, if you can give me any insight, it will be very cool. So let me break down that experiment a little bit. Yes, please. So typically what rats will do when they engage in an aggressive encounter, right, what they will do is they will swing around to bite the lower flank or rump area, right? Or if they're hyperaggressive, what they'll do is they'll lunge directly at the nose. So bite right at the front of the face, right? So they're the two major targets of attack. Now, if you can set up a situation where you can make one rat the attacker and the other rat the defender by having the animals, so you have one rat, typically male because they tend to be the territory holders, in its home cage and introduce a stranger. Okay? Now, the territory owner, he will attack and try to bite the other one on the rump or on the front of the face. The other one, it doesn't want to get into a fight. It's just trying to defend itself. So it now engages strictly in defense.

And what it will try to do is adopt strategies to block the other rat from getting access to the rump and block it from biting it on the front of the face. One of the things that the defending rat can do is when the other one lunges at the rump, is for it to lunge down and bite it on the side of the face. So the side of the face is a defensive target. Interesting. The nose and the rump are offensive targets, right? Now, in that context, when you look at what happens in that so-called induced aggression and you look at, well, yeah, you hit them with a jolt of electrical current and now they lunge at each other and bite. Where do they bite? The side of the face. Not the rump, not the nose. So it's a misnomer to call it aggression. It's induced defense. The rats are thinking, I'm being attacked, so I've got to defend myself. And so they're counterattacking in a defensive way, targeting the side of the face. Wow. Mind-blowing. Yeah, very, very interesting. And how much contingency makes a difference? Like if they understand why it's coming or it just comes out of nowhere, is that a factor for that aggression? Yeah, because it's... Because it seems like, typically, it seems like it's such a setup that they have no really other option to do, right? Yeah, yeah, yeah. And again, the problem is that it's an innate response because the animal is experiencing sharp pain. There's someone there to blame. You're going to defend yourself. And it's really hard to teach them not to do that, right? Yes. So, but where the contingency does come in is, and this has been done with looking at those resident intruder kind of encounters, where you're dealing with a relatively small cage, so, you know, maybe like this, where the animals haven't got much room to move, or in an enclosure which is the size of my room here. And what the intruder will do as soon as the other one approaches, the resident approaches, is run away. Go. Yes. So that's your preferred choice. And the only reason why you then turn around and try to defend yourself is if the resident gets you in a corner where you've got no choice but to physically fight. What about any other, like, any interesting studies that you have done, any experiments that are worth sharing, that people like dog trainers, for example, wouldn't know, but they actually have some place, something for us to consider? Is something comes to mind that in your, all of the years that you've done, that most people would not really even think of? Or maybe they do as something, okay, that's unintuitively, it's right, but there is actually, we've done this, we understand that.

Not so much a specific experiment. Well, I'll lead this into an experiment in a minute. But most critically, I think one of the mistakes human observers make is that we tend to interpret what other animals are doing from our own species biases that we have, right? So, and you can see this in the way rough and tumble play has been suppressed in schoolyards amongst children. Because many teachers, especially, especially female teachers, will view any kind of roughhousing as aggressive, right? Whereas it's not. Whereas it's not. And I'll tell you why it's not sexist, because experiments have been done where they've compared women teachers who grew up in household with brothers versus households with sisters or no siblings. And the ones that grew up with brothers are better at detecting when the rough and tumble play is really playing when it's aggression. Which means a personal experience really is important, right? So, taking that. So, there is a problem, and we articulated this in one study we did with dogs, where even human researchers studying dogs have interpreted rolling over on your back as a submissive gesture. Mm-hmm. Right? Right? Which it can be in some situations. But when you look at the details of what's going on in the particular study we did, what we found was when the dog rolled over, what it did is it used that as a vantage point to lunge up and bite the other one in the throat. Right? So, it's a way of defending your nape by rolling over and saying, actually, we did this by looking at a particular dog who was a particular snake. And pairing it up with partners that were bigger, and so I had an advantage of getting to the nape, or partners that were smaller, and so I had a disadvantage. And this dog, a she, what she did was she was more likely to use the rolling over onto your back against bigger dogs because they had this relative advantage of gaining access to an ape. And then she used that position to counterattack. So, whereas with smaller dogs, she was more likely to be one biting the nape, and she did very little on the back roll over. So, again, you look at this and you go, so she's using this strategically in the context of how best to continue the play fight going on. And in one case, being on your back is more advantageous. In another case, it's not. It's got nothing to do with dominant subordinates. Right? Yeah. So, the one advice I would give to your colleagues who do dog training and think about dogs is try to look at it from the point of view of the dogs.

Don't look at it from the point of view of what you think is happening because if I was, if it was me, this is how I would interpret it. That's one of the, probably the hardest lessons for anybody studying the behavior of someone else. Something different. It's easy to see the problem and what they're doing through the eyes of the participants, not through your own view. Excellent. Excellent point. Wow. Yeah. And so now let me go to the experiment side. And this has been done both in an experiment I know with dogs and some observational and physiological work done with horses is that two animals can be interacting. And so physically, it looks like it's play. Right? Right. But when you measure stress response hormones in the participants, what you can discover is, wow, yeah, it looks, it looks like play. Right. But one of the animals had no stress response because they were enjoying this immensely. But the other one showed us a spike in the stress response indicating that this was not a pleasant experience for them. So again, even just the physical appearance of the behavior is not sufficient to really often tell you what the experiences of the participants are. So you need more subtle cues, either more subtle behavioral cues or where you have available physiological responses to the situation. So I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I would say I And typically, the female will kind of get very pissy, and the male's going to back off. But if it's two boys or two girls, they will escalate very quickly into a fight. Happens with rats and other species, and why do you think, if you think that there is that dynamic in the play between the different gender? Yeah, so there's two things that the audience should know. We've actually done the experiments now

of finding a way of manipulating the play experience of both males and female rats. And what we've shown is that the play experience has the same effect on the medial prefrontal cortex in males and females. So both males and females benefit from the play experience as juveniles. In adulthood, and a lot of the cases of the dogs you're talking about, you're dealing with adult dogs, in adulthood, rats continue to use play as a means of social negotiation and navigation. In particular for rats, it's used to assert or test dominance. And since the sex that is most motivated by gaining dominance is males, you see exactly what you just said. Under some conditions, two males will start playing and this can end up escalating to serious aggression. Adult females don't use play as a dominance testing behaviour. So their play, when they do play, tends to be gentler and so they rarely get into situations where any escalation is possible. But again, adult males playing with adult females, the females will very quickly show the more submissive pattern of play. So it's a little bit different to what you're seeing in dogs. Yeah, yeah. But for example, in hamsters, where as adults they're solitary, as you go towards the end of the adolescent period before they leave the maternal nest or territory, the females are about twice as big as males. So the reverse is the case. It's the case that the males will quickly show a more subordinate behaviour during rough and tumble play if it escalates to a more forceful thing. So it depends on the species and the social system as to which sex has the advantage. How often, like if they're let alone and they have the choice, how often play encounters happen with mice? Not mice, with rats. Rats. Yeah. Well, somebody's actually measured that. They looked at over a 24-hour cycle. So just litters of rats growing up, looking at them every hour for 24 hours. And what they found is that under captive conditions like this, about an hour of the day is spent playing. Wow. Wow. It's quite a substantial amount. So, yeah. I mean, totally, I can see why it's worth spending time studying them if it's so exuberant. Yeah. And like, if I go back to my PhD, which involves studying Australian magpies, this playful bird, I was studying them in the field. So I looked at their activity period from dawn when they woke up, to dusk when they went to sleep. They're inactive during the night. So I just had to deal with the daylight hours. And for the peak juvenile period, the average amount of the daytime they spent playing was 20% of their active time. Wow. So it's quite substantial. I have to Google that one because I don't think even,

maybe I know it, but it just doesn't come visually what that bird is. Yeah. It looks like our North American magpies. Okay. It's just a slightly different bill, longer beak, but it's black and white like our North American magpies or European ones. With the rats or with anybody, have you done anything as far as how psychotropic medications would affect the brain and especially play? We haven't done much with that, but there's a lot of other laboratories have. And yeah, I mean, it depends what you're given as to whether you play or not. So for example, things like amphetamine will tend to, and cocaine will tend to suppress play. So the animals don't engage in play, but opioids will tend to elevate play. So... What about the, like the typical, like the prozac type, like the psychotropic, like, you know, that are given for depression, PTSD and all that stuff? Yeah, yeah, yeah. So yeah, that tends to increase the playfulness. Interesting. Yeah. I guess one of the things when we talk about play and we talk about, you know, how we mentioned the aversiveness, the discomfort and the cooperation and you basically really tap into this fight-flight type of responses, which now, the kind of the typical, the, not the typical, but it used to be that true in brain kind of thing to where the lizard brain and, you know, and it's really like, truly just different compartments in the brain and flight. And now we understand that, you know, they interact and all those decisions are, they have a very different, more broader functionality than that. Anything interesting in terms of that because it's like, quite often we are stuck in, especially in dog training, it's like, well, it's fight-flight-freeze and they're, you know, like, like looking at them almost as very independent actions or reactions and that seemed to be not the case anymore. Like, it's kind of outdated, right? Yeah. I mean, again, it's like cooperation and competition. it's, you have to rebalance flight and fight depending on the context, depending on who you are, what the situation is, what the threat is. Right. Because it's mostly just that, the uncertainty and then, you know, you pick up strategies, but it's more complex than just that simplistic explanation that used to be before. But, I think I want to leave you with a really, because it's not quite dealing with fight and flight, but, it's, it relates to using the animal's brain to try to get insight into what it knows. So, here's, here's this beautiful experiment that's been done by a German team and it's just fantastic. So, rats, will enjoy being tickled by people. Right. And it becomes a form of play. So, you get the rat and you tickle it and it enjoys it, runs away, comes back, gets to tickle some more

and so on. And so, what they used was using this tickling as a reward to get them to engage, to learn how to play a particular game. And the game was hide and seek. So, you put a rat in a box and then when you release the box, it goes into this big room and there are objects like boxes, walls, some made of plexiglass, some made of things that you can't see through, etc. Right? And then they had two conditions. One condition was the rat had to come out of the box and then go and hide and the human experimenter would try to find them. And when they found them, they tickled them. Right? The other condition was the human experimenter was hiding and the rat came out of the box and it had to go through the room to try to find where the experimenter is and if the rat found them, then the experimenter would tickle them. Okay. So there's several really valuable lessons out of this. One is they used electrodes in the medial prefrontal cortex to record what's the medial prefrontal cortex, what's the activity there during these games. The other one was they recorded the vocalizations and then the third is they looked at what's the behavior they engage in when they're hiding and when they're seeking. Okay. So let's deal with seeking first. No, sorry, hiding. When they're hiding, they preferentially hide in locations that you can't see through. So if there's a choice between a box that's made of plexiglass or a shoebox that's made out of cardboard, they preferentially hide in the shoebox. So they seem to understand that I can hide where you can't see me. Also, when they're hiding, they stop vocalizing. So rats have this rich repertoire, particularly of 50 kilohertz calls that they emit when they're in a happy state and they stop calling. So not only do they hide where they can't be seen, but they shut up. So they're not giving away their location, right? Good players. And when you look at the activity of the medial prefrontal cortex, it shows a particular pattern of activation, right? when they're seeking, they're moving around and they tend to move and look behind places where they can't have a visual line of sight. So they're looking for places where it makes it more likely that somebody's hiding. they don't refrain from calling because it doesn't matter whether the recipient knows whether you're calling or not. And when you look at the medial prefrontal cortex, it has a different pattern of activity, right? So the firing pattern is different. So that means that if you think of the vocalizations as representing some emotional content, right? Right. So you know that emotionally this is probably where they're thinking about strategies, how they're thinking about the situation is different, and their behavior shows that they can tell the difference. Like to me that is, my God, that's so fantastic.

For sure, that's mind blowing, especially thinking it's still around. It's insane. Wow, that's insane. Thank you for this. So I'd like to leave your audience with the idea that as our neuroscience techniques are becoming more sophisticated, we can actually overcome that problem I said of, you know, just observing and you see behavior look similar and you give it a particular value. You can now get other insights from the brain about what the animal is thinking about what it's doing or feeling about what it's doing and so actually get the animal's point of view of the behavior. Insane. this is just yeah, that's insane. I wish I was back as a graduate student again so I could start my career again because this is just out of sight. But to finish here, what is of interest to you right now? What are you focusing on? Like anything that you're exploring and like where are you right now? Because you've done so much that what is the next frontier? Where are we going? Yeah, so I'm getting at an age where I need to start looking at wrapping things up. I'm not going to be around for another 50 years. So there were two major questions I'm trying to pursue over the next five years. One is with the rats and the question is okay, so experimentally we've shown that if you deny the rats the opportunity to engage in the right kind of play, you have this reduced social skills and altered brain development. Right? But what made me think about this was a few years ago, when you look at the error bars, they're very big, right? Both in the control animals and in experimental animals. So you go, well, that means different individuals are responding, even though it's a group that's showing this difference. Individuals are showing some market effect and some are showing a minimal effect. So now what we're doing is using rearing groups of animals together and then looking and tracking on a daily basis the amount of play they're doing, the type of, and we're filming it, so we're looking at the experiences gained from the play you're doing, and then we're looking at the social skills in adulthood and then the development of the medial prefrontal cortex. And early days, but what it looks like is not everybody benefits equally from the play. So some gain a lot of benefit and some little or nothing. So it means that that has implications for promoting play as the panacea for all humanity's problems. It's not. It's good for a majority of people, but it doesn't necessarily benefit some minority, which then from a practical point of view then raises the issue of, which is one of the things that probably my graduate students will pursue over a career, is identifying what makes the animals that don't benefit from play, what identifies them as that kind of animal? Is it genetics? Is it the maternal

experiences they had with mothers early on? That biases their ability to gain the benefits from the play? Because if you know that, then you can translate that to humans to identify which kids in this schoolyard are not benefiting from play, and so what other strategies could we use to help them build up those skill sets other than through play? That will be super valuable and very interesting thing. What is the lifespan of a raft? What are we talking? About two years. Which is actually good for experiment, right? Yeah. So we've gone well into, like, by 100 days, the animal's quite old. And we've taken rats up to about 140 days. And so we could establish what things remain stable over the age post-juvenile and what is changed. So, yeah, it's a manageable age span. Yes, yes, very cool. Dr. Peles, thank you. This was just this amazing conversation. My pleasure. Thank you. I mean, we went all over the place and it was just really, really interesting. I cannot wait to myself go back and listen to it. It was just very much, so very much appreciate you joining in. My pleasure. Thank you. again for inviting me to have this conversation. Take care. Thank you.