BJKS Podcast

93. Nachum Ulanovsky: Bats, spatial navigation, and natural neuroscience

February 09, 2024
BJKS Podcast
93. Nachum Ulanovsky: Bats, spatial navigation, and natural neuroscience
Show Notes Transcript Chapter Markers

Nachum Ulanovsky is a professor at the Weizman Institute. We talk about his research on spatial navigation in bats, how Nachum started working with bats, the importance of natural behaviour, how to build a 700m long tunnel for neuroscience, and much more.

Support the show:

0:00:00: How Nachum started working with bats
0:09:29: The technical difficulties of working with bats and in a new species
0:16:03: The Egyptian Fruit Bat
0:19:42: Wild bats vs lab-born bats / spatial navigation in very large spaces
0:26:28: How to build a 700m long tunnel for neuroscience
0:44:30: 2 random questions about bats
0:53:48: The social lives of bats & social place cells
1:05:09: Why are there so many types of cells for spatial navigation?
1:13:01: Natural neuroscience
1:17:33: A book or paper more people should read
1:20:39: Advice for PhD students/postdocs

Podcast links

Nachum's links

Ben's links

References & links
Bracken Cave in Texas, with millions of bats:
The Onion video on scientist who wasted life studying anteaters:

Eilam-Altstadter ... (2021). Stereotaxic brain atlas of the Egyptian fruit bat.
Eliav ... (2021). Multiscale representation of very large environments in the hippocampus of flying bats. Science.
Finkelstein ... (2015). Three-dimensional head-direction coding in the bat brain. Nature.
Geva-Sagiv ... (2015). Spatial cognition in bats and rats: from sensory acquisition to multiscale maps and navigation. Nat Rev Neuro.
Geva-Sagiv ... (2016). Hippocampal global remapping for different sensory modalities in flying bats. Nat Neuro.
Hafting ... (2005). Microstructure of a spatial map in the entorhinal cortex. Nature.
Hodgkin & Huxley (1952). A quantitative description of membrane current and its application to conduction and excitation in nerve. The J phys.
Hubel & Wiesel (1962). Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. The J phys.
Lettvin... (1959). What the frog's eye tells the frog's brain. Proceedings of IRE.
Miller (1956). The magical number seven, plus or minus two ... Psych Rev.
O'Keefe & Dostrovsky (1971). The hippocampus as a spatial map ... Brain research.
Omer ... (2018). Social place-cells in the bat hippocampus. Science.
Sarel ... (2017). Vectorial representation of spatial goals in the hippocampus of bats. Science.
Sarel ... (2022). Natural switches in behaviour rapidly modulate hippocampal coding. Nature.
Tsoar ... (2011). Large-scale navigational map in a mammal. PNAS.
Ulanovsky ... (2003). Processing of low-probability sounds by cortical neurons. Nature neuroscience.
Ulanovsky & Moss (2007). Hippocampal cellular and network activity in freely moving echolocating bats. Nat Neuro.
Yartsev & Ulanovsky (2013). Representation of three-dimensional space in the hippocampus of flying bats. Science.

[This is an automated transcript with many errors]

Benjamin James Kuper-Smith: [00:00:00] Yes, I mean, I'm really looking forward to kind of, uh, this conversation because it's, it's first it's on a topic I've been interested in kind of as an outsider for a while and, uh, I think from what I can tell you do pretty unique research in this area about adding kind of a very different perspective on topics that I've heard about, you know, done in other species, that kind of stuff. 

So yeah, I'm really looking forward to kind of exploring the topics and especially what I'm interested in talking about more is kind of How you started working with bats and talking about bats themselves, the ecology, what, you know, what bats do, how they live, that kind of stuff. And I thought maybe the easiest way to kind of do that is to kind of track your education until you started working with bats, because from what I can tell you didn't start off that way. 

So maybe as a, as a kind of first question, I saw you studied physics for your bachelor's, so kind of, what were you, why did you study physics? What were you kind of, what do you think you were, you were going to do with, [00:01:00] with that? 

Nachum Ulanovsky: So, uh, as a kid I really loved, uh, you know, I loved math, I loved physics. also loved, uh, you know, zoology. I was, uh, watching, uh, You know, BBC documentaries, David Attenborough and such, so My mom, uh, always thought when I was a kid that I'm going to go study biology, zoology, something like that and I surprised her by going to physics that's because, you know, I love that topic as well, especially math, so Of course, the funny thing is that, uh, after studying physics, then going to neuroscience and ended up studying Doing research in neuroscience in bats, uh, including in, uh A natural behavior. 

So ended up coming back to zoology in a way. So I guess you can't escape your, uh, childhood, uh, loves 

Benjamin James Kuper-Smith: Yeah, but you, so you wanted to, did you have like a particular career in mind when you started, uh, or during your degree, or was it just your interest in the topic and let's see what happens? 

Nachum Ulanovsky: I really, I loved physics, so I stu [00:02:00] I, I, I, you know, I studied physics and then I, I went to the army, which was, uh, sort of, uh, you know, in Israel, all, all, everybody have to go to the army. So. naturally introduces a gap in your academic career because I, I did my PhD, uh, my, sorry, my physics undergrad before the army. 

So then I went to the army and then this created a gap. So it gave me a, an opportunity to consider what I want to do next. And then. while I was still in the army, I was more than five years in the army, I was exploring all sorts of directions. I decided I want to go into biology, that my quantitative background is useful for biology. Today, it's very common to think this way, but back then it was a bit less common. So I, for a year, I took all sorts of undergrad courses and you know, cell biology, genetics, biochemistry, stuff like that. Then for another year, I took courses in neuroscience. So, for about years, I was meandering until I decided that [00:03:00] neuroscience indeed is what I wanted to do. 

So, it was a bit of a to even go into neuroscience. And then I did a PhD in, in neuroscience, but not in bats. I, I actually worked on auditory cortex in cats Nobody, almost nobody studies cats, but, you know, back then, I mean the, in the nineties still, and of course before that, cats were the standard animal model for sensory neuroscience and all the big discoveries of huble and weasel and, and visual neuroscience. 

And then, uh, likewise in, in, uh, in the auditory do, uh, uh, domain. Everything was done in the 50s and 60s and 70s and 80s in cats, almost everything. I mean, I still remember as a PhD student in the late 90s, hearing for the first time about a lab that started to study auditory cortex in mice. I said to myself, you know, this is weird. 

Why mice? They barely hear. This is a weird animal model to use. Nowadays, [00:04:00] everybody's doing everything in mice. But back then, it sounded like a weird idea. And so, you know, I completed a very successful PhD, successful in terms of findings and publications. And I could have easily continued, you know, working in mainstream neuroscience, let's call it this way. But I decided to change direction, you know, for my postdoc and a number of reasons. So one is that during my PhD I found some effects in the auditory cortex of cats that sort of memory related or were dependent on the history of the stimulus. So I got interested in memory, started reading about memory, and then, of course, you bump into the hippocampus, and you read about place cells and all that. 

Grid cells did not exist back then. I thought to myself, wow, this is really amazing. Of course, I heard about place cells in courses, etc., but it's different when you start reading papers, But then I saw there's so many labs worked on place cells in rodents, and I guess I just want to do something else. 

You know, if everybody are working in rodents, I just want to do something [00:05:00] else. That was sort of one direction of how I started to look for which would be an interesting species to work on. Then I also, because I worked on auditory neuroscience, I knew about bats. I didn't work on bats, but bats are actually quite a substantial or an important animal model in auditory neuroscience. 

So I was, you know, seeing lectures, posters on bats. So I knew about them. you know, more than the average neuroscientist, let's put it this way. And then the third thing, I took a course in neurotology and this really blew my mind. I really decided that looking at the neural basis of natural behaviors, that's, that's the way to go. And so, you know, it was a convergence through several directions and it took me several years. It wasn't like an overnight decision. It took me a couple of years to converge on this. And, you know, also, if you, if you start thinking, If I want to study the hippocampus and want to study the neural base of behaviors, but I don't want to do it in rodents, because everybody are doing it in rodents, which would be a species that you could work on? 

Of course, you know, [00:06:00] elephants have great memory, so probably an interesting species for hippocampus studies, but not very practical. So if you think of a practical small mammal, and I did want to work on mammals, about which quite a lot is known, maybe not so much about neuroscience, but in terms of their natural behavior, And that's come pretty much on top. 

And then they have also the various interesting properties that you can, that we've been exploiting over the years. They fly in three dimensions, so we can ask questions about how is three dimensional space represented in the brain. They fly fast, so which can ask questions where the speed of movement per se is important, and I can give you examples later on. Uh, they have two distal sensory systems, both vision and echolocation, so we can ask how is the same space represented by two different sensory systems that are distal, that are from afar, and we don't have something like this, and rodents don't either, so that's an interesting advantage. We can measure the timing of their sensory inputs very precisely. [00:07:00] By putting a microphone we can record the timing of sensory input with a millisecond precision in freely moving animals. Again, something that's not so easy in some other freely moving animals. So there is a whole host of advantages to using bats. Of course, they're very social, So, so, you know, I had a number of parallel reasons through which I eventually converged on this direction of going to bats. 

But this wasn't an easy choice because nobody worked on hippocampus before. in that so my postdoc was the first time anybody did that so this was definitely a scary jump into the cold water to to go in this direction 

Benjamin James Kuper-Smith: Yeah. Um, I mean, you said that, uh, grid cells hadn't been discovered then, but I guess by the time you, you did your postdoc, they, the 2005 paper, I think your postdoc was 2004 to seven, right? Something like that. Uh, so that came out, was that kind of also, um, motivation for you to continue working in the field because it kind of obviously big things were happening in the field or [00:08:00] was it not even that obvious at the time when these things came out? 

Nachum Ulanovsky: no i think it was very obvious to anybody in the field this is a big a big thing You know, at this point I was already committed to this direction, so I don't think this changed anything, but it actually, it added pepper, so to speak. It was clear that there is, uh, there are more things to do. We can also look at grid cells now, which we, we did eventually, uh, so that was definitely, uh, and you know, the funny thing is that I used to, um, I was working on the bat hippocampus, hippocampal recordings on the bat place cells, sort of in parallel to the Moses and to Halting and Mariana Finn, the two PhD students who, who did the work on the, on the, on the grid sales. 

And, you know, at SFN every year we would meet up in the SFN is a Society for Neuroscience annual meeting. We would meet, uh, every year in the alleyways of the sort of hippocampal posters. And, and we, we sort of used to have people asked us the same question. They sort of wanted both them and me. People [00:09:00] wanted us to do, like, everything at once, you know, do a study on renapping, do, uh, manipulate this, manipulate that, and like, we used to joke that, you know, we can, you can do everything simultaneously, we've been working on, for decades, on place cells, and they wanted, you know, me to do everything at once on, on that hippocampus and, and them on, uh, on, on rodent grid cells. 

So it was sort of a funny parallel. So I, I was very aware of this because I was talking to these guys a lot in real time during my postdoc. 

Benjamin James Kuper-Smith: Uh, I mean, you mentioned earlier that, you know, bats have all these advantages for studying, but there's Well, I don't know how much of a disadvantage it is, but to me it sounds like a massive disadvantage that Maybe you could clarify kind of what, what the technical standards were at the time, like was it, to me it seems like it would be harder to record from something flying around in 3D than from a rat moving around in a small box. 

Did you have to like develop, I mean, for example, you know, the, the, you know, you have to store the data somewhere. And from what I imagine, usually that was done with a cable at the [00:10:00] time. I imagine that's not exactly ideal with bats, so you need some sort of way to transmit the data. And I'm curious, like, was all of that already in place in 2005, 6, 7, or whenever you, you know, exactly started working on this? 

Or was that kind of, did you have to develop all that technology, um, to make it actually possible to study bats? 

Nachum Ulanovsky: Yeah, no, no, we had to develop a lot of things. So even before, so, okay, let me restart. So we had to develop, uh, all of that. In my postdoc was on big brown bats, and then I moved back to Israel to work on Egyptian fruit bats, which are a lot bigger. And this is a big advantage. So during my postdoc, you had to start somewhere. 

So I did a basically comparative approach where I would I recorded in big brown bats while they were crawling in a two dimensional arena. So I sort of redid the rodent experiment, but doing it in bats. So, okay, I needed to set up tetroid recordings and [00:11:00] solve some technical things, but there were still wired tetroid recordings. 

So this was very similar in many ways to rodent experiments. Okay, setting up for the first time in a new species, but nothing extra, extraordinary, I would say. Uh, and the lab where I did my postdoc lab of Cindy Moss, they worked with these species so, you know, I could learn from them. techniques, etc. 

So this, this was, uh, was a lot to do, but this was not, uh, a completely new species, or this flight issue that you mentioned. Uh, so this was something I definitely was able to do during my postdoc. And then, when I moved back to Israel, let me, uh, sorry, go back for a second. During my postdoc, I was working also on, on developing together with a company, Neuralinks, developing a, a wireless telemetry system for recording in the, in the big brown bat. 

And this was a, an iterative process that took, you know, three years, pretty much, almost three years, maybe two years where we were working on [00:12:00] developing this telemetry, uh, system. And it worked. The telemetry system was developed, went through several generations, but it ended up still being too big for the big brown bat. 

So big brown bats are called big, but they're really small. They're 15 to 18 grams. They're only called big because they're bigger than the little brown bat, which is six grams. So, you know, big is in the eye of the beholder. Um, so there was no way they're going to, to fly with this system, which was too big for, for the, for the big brown bat back then. But then When I moved back to Israel and started my own lab and switched to the Egyptian fruit bats, which are 10 times bigger than the big brown bats, they could already carry this system. So sort of, I used to tell people my low tech solution to the miniaturization problem was to increase my animal tenfold. 

This is, this is 

Benjamin James Kuper-Smith: Yeah. 

Nachum Ulanovsky: way to go. So this is what I did, but still we continued miniaturizing things. So basically, When I started my lab, I took the system, the wireless system, the wireless telemetry neural recording system that [00:13:00] we developed during my postdoc with NeuralInks and applied it to the Egyptian fruit bats and, and it worked very well because they could easily carry this, uh, this weight. 

That basically, uh, Mikhail Yartsev was my PhD student. He used this system that I developed in my postdoc to, to record from the bats. So it worked really well. And then later we switch to a different system or develop a different system with an Israeli engineer, which is approach. Instead of transmitting the neural data, we switch to a neural logger system or neural logging system that is means storing the data on board the animal, which has several three main advantages. 

One It is unlimited in distance, so if we want to go to studying neural representation of very large spaces, then, you know, we are essentially unlimited in distance. The second thing is that it takes up much less battery power to store the data as opposed to transmitting it, so you can miniaturize battery and make everything smaller, which is a big advantage. And third, it also, [00:14:00] whenever you're transmitting stuff, you're sensitive to noises, et cetera, interferences, which you can try to block, et cetera, but if you're recording right there on the animal, you don't have these issues at all. So it's also, by definition, a better quality of data. So, so these are like the three main advantages. 

So we switch to this neural logging system. And over the years with this company in Israel, Deuteron Technologies, we were developing already more or less four generations of these neural loggers that got smaller and smaller over the years. And now the 64 channel neural system that we're using now is smaller than the 16 channel system that we used, you know, six or seven years ago. 

So things have been miniaturized dramatically over the years. And, and there are other things that you need to solve, by the way, just, uh, you're asking about introducing a new animal model, there are more basic things, for example, when I started working on the Egyptian fruit bats, we did not have brain atlas, it's something that's very basic, anybody working with rodents, [00:15:00] monkeys or standard animal models, they have an atlas of the brain so they can use it to direct recordings inside the brain. 

We did not have that, so we had to do our own atlas. It was, uh, 12 years of work, which a couple of years ago we published this as a book, but this was actually a lot of work to construct a stereotactic brain atlas. there are the things like anesthetic regimens that are different between species. You need to figure that out. 

This is not too difficult because, you know, you played a little bit in two or three animals and then you converge on something. So there is a little bit of overhead with starting a new species. It is not that Difficult, in a way. Atlas is the main thing that you need to solve, the other things are pretty solvable. 

As long as you do it's not an issue. The molecular methods that exist in mice, of course, are not easily transferable, or some of them are not easily transferable to other species, but as long as you do electrophysiology, you record electrical activity, it doesn't matter which kind of a brain it is. 

It's the same thing [00:16:00] in a rat, or a mouse, or a bat. 

Benjamin James Kuper-Smith: Okay. Um, I mean, you mentioned a little bit why, like one of the main advantages of the Egyptian fruit bat being that it's relatively large. I'm curious, like, was that the main reason? Uh, and that it, it also exists in Israel or kind of why did you decide on that? I mean, did you have like a big process where like, oh, there's, you know, because there's so many species of bats, um, like which one do I go with? 

Or was it pretty clear that this was the only one that was going to work? Um, 

Nachum Ulanovsky: No, this is pretty clear that it's the only one that's going to work for two main reasons. One is the size, which is, uh, on a technical level, very important. And the second, it's also very common, uh, in Israel. So there's no problem of, uh, of getting permits to capture them. Back then, they were even considered agricultural pests. Um, now, not anymore, but, you know, they're so common that it's not an issue at all. Whereas a lot of the other bats species are protected. So that's much more, much more of a problem. Uh, with the Egyptian fruit bats, we're essentially unlimited in the numbers of animals that we can use. [00:17:00] Not that we need big numbers. 

I mean, through the entire lifetime of my lab, we've probably done experiments, uh, like on the neural recording experiments, we've probably recorded, I think, on the order of 100 animals over all the last 15 years. It's small numbers, relatively speaking, but anyways, there's no problem to get permits with such a common species. 

Benjamin James Kuper-Smith: And so then, how does it work? You just find a cave where they are and you bring a, a net and then you catch them yourself? Or, uh, how, how do you, how do you get there? Because from what I understand, like, if you study something like mice or something, there's, you know, all these different kind of mice you can buy that have like certain genetic properties, etc, etc. 

But I'm assuming that doesn't exist for an animal that is rarely studied in this way. So how, do you actually just catch them yourself or how do you get them? 

Nachum Ulanovsky: Yeah, actually, that's exactly right. We catch, I catch them myself. So the way it works is I know several dozen caves or cave like structures. These bats live in caves and it's easiest to catch them in the cave during the day when they're resting. [00:18:00] Um, so I know several dozen places and, um, about three or four of them are relatively convenient for capture for practical reasons. 

The ceiling is relatively low. They're accessible. Whatever. I mean, it's just this practical reasons. And yeah, we come during the day. I do the catching myself. We come me and the vet and usually another person and, uh, you know, using a telescopic pole like for painting with a butterfly butterfly net. I just put it under under the bats. 

It's not, you know, I don't, uh, you know, sort of them, so to speak, off the ceiling. You just put gently the net under the bat, and the bat is trying to take off, but because of gravity, they're hanging on the ceiling. Because of gravity, when they take off, they sort of fall down, and they fall down just straight into the butterfly net. 

So it's very easy to capture several dozen bats within a few minutes like that. So, you know, once or twice a year we go and capture bats. It also means we are working with wild animals. We also have a breeding colony in [00:19:00] the, in the Weizmann Institute where I'm based, but we, we mostly over the years been using wild animals, which is another interesting advantage. You know, you're studying the neural basis of navigation in animals that have actually navigating outdoors were caught as adults in the wild. Or if we are looking at social aspects in the brain, these are animals that have. lived in colonies of thousands of animals. They had a lot of social interactions and were only caught as adults. 

So I think this is an interesting advantage as opposed to, you know, inbred rodent species that are, could be different. It's hard to know, but in our case we, we, we work on the, uh, on the wild animals, which I think is, is, is definitely an advantage. 

Benjamin James Kuper-Smith: I think in one of your papers at least, um, you had this comparison between the wild bats and the bats that kind of grew up in the lab. Um, so just briefly, just because you have that kind of comparison, uh, kind of what kind of differences do you find? Like, does it make a difference whether you have them born in the lab or caught in the [00:20:00] wild? 

Or are there some differences in their behavior and, and neural recordings? 

Nachum Ulanovsky: So, in behavior, yes, bats that are born in the lab that are used to humans from, from, uh, birth, they're, you know, much, uh, more friendly and maybe easy to train. There's some difference in the behavior. I mean, the wild bats are also, uh, very easy to train and to work with. Egyptian fruit bats are very, um, I would say tame bats in a way. 

They're not aggressive at all. So, uh, so it's very, uh, very easy to work with them, very easy to, to train them. But the ones born in the lab are even more you know, more friendly. It's like, a way, it's almost like a cat that was born on the street and grew up on the street versus a cat that was born at home. 

I think any, any cat owner like myself knows the difference. Um, uh, this is sort of a wild animal and this is not. So there is a difference in the behavior. In terms of the neural side, I think it's an interesting and important question. We have not explored [00:21:00] it systematically. this one study, uh, where we looked at this, we did was actually, you know, we asked a very general question. 

This was, um, a study where we asked, uh, about the representation of very large scale spaces. Maybe I should before that, just to give us a, give a, a background about the types of neurons that we are studying to understand. So. There are three main types of neurons that people have been studying in rodents over the years that relate to space. There are place cells, neurons in the hippocampus, that whenever the rat or the mouse are running in a sort of a small box, one meter in size or so, whenever the rat or the mouse are in a particular corner of the box or in the center of the box, in a particular location, the neuron will get activated, sort of in this one location. And this one location, uh, is called the place field of that neuron. And these neurons were called place cells by John O'Keefe, who discovered them in the early 70s. Then there are grid cells who are activated not in [00:22:00] one location, but in a series of location. Whenever a rat or a mouse passes through a series of location that form a hexagonal lattice that span the environment. So place cells are thought to be like a cognitive map of where I am in space. Grid cells may be a cognitive distance meter, represent distances. And we also have cognitive compasses in the brain called head direction cells, neurons that represent, uh, not so much about, don't care about position, but they respond whenever the animal's head is pointing in a particular direction. sort of like a neural compass. So we have maps, distance meters, and compasses, all the elements that you'd like to build a navigation system in the brain. And basically, all of this was studied typically in animals moving in very small, empty environments. what we've been asking over the years in the brain is how does real life navigation differ navigation in small empty boxes and you can give several answers one is that the world is three dimensional so [00:23:00] how is two dimensional space represented in the brain and you know we've done quite a lot of work on that which i'll i'll tell you uh soon um you can ask how do we navigate to goals because places tell you i am here But, you know, how is the goal represented in the brain, where you want to get to? 

It's a different question, and we've done work on that as well. Third answer is that, you know, we often navigate in groups, animals often navigate in groups, and so how is the social factors come into play? And we'll talk about the social aspects later. And lastly is the issue of spatial scale. Of course, uh, normally in real life. Humans or animals do not navigate in one meter boxes. We navigate in much larger spaces. And of course, nothing was known about how our very large space is represented in the brain. So to do this, we constructed a very large tunnel, a 200 meter long tunnel at the Weizmann Institute. Now it's 700 meters long. And, uh, we, uh, developed those neural loggers [00:24:00] that I told you about, uh, before. These wireless recording devices that store the data on board the animals. So now we are unlimited in distance. And now we can record and, uh, you know, we measure the position of the animal using not a GPS system, something more, you know, about, 10 or 100 times more precise than GPS, where you measure distances from a tag on the animal, a radio frequency based tag on the animal, to an array of antennas that we position around this tunnel. 

So we can measure the position of the animal with about 5 cm precision nowadays. And so we measure the, the position of the bat, the neural activity, and now we can look at place cells in the hippocampus in these large environments. And what we found, and this published in, in science a couple of years ago, in small environments where neurons are active in one location, so sort of these place fields that I mentioned are sort of Gaussian small place fields in one location, in this very large environments, Each neuron was active in many locations, and [00:25:00] surprisingly, these many place fields of one neuron could vary a lot in their size. 

So the same neuron could have a 1 meter place field in one location and a 20 meter place field in a different location. So it's sort of a multi scale or multi resolution type of a neural code. And we showed, we had also a computational, a theoretical component in this study, and we showed that this type of a multi field, multi scale neural code is much better, two or three orders of magnitude better than the classical place code in terms of decoding accuracy. And when we saw this very surprising type of a multi field, multi scale code, we also looked at whether in lab born bats we'll find the same because this was all done in wild born bats and then a very natural question to ask is if you take a lab born bat that has never seen hundreds of meters in his life before, we find the same thing? thought that we will find something different and very surprisingly or even shockingly for us we found the same type of neural code [00:26:00] also in the lab born bats. So exactly like in the wild born bats we found this multi field multi scale code also in the brain of lab born bats with very similar characteristics. So this suggests that this is an innate, this multi field, multi scale code is an innate property that's very fundamental to the function of the hippocampus regardless of experience. 

Benjamin James Kuper-Smith: Yeah, it's, it's, it's a really cool study. And I mean, just from a, just from a practical perspective. How do you go about building a 200 or now 700 meter long tunnel? Uh, I mean, it's not, you're not, I'm assuming you're not digging underground for a tunnel. It's just, so bats have a tunnel to fly through. Um, but I mean, is it? 

I'm curious. Yeah, it's just like, how do you? Because I guess you need, you know, usual, usual neuroscience labs aren't 700 meters long. Uh, so I guess you have to have some sort of large area of land where you can actually do this and then actually make it happen. So I'm curious whether you [00:27:00] could comment just on the practicalities of kind of setting up this very unusual kind of lab. 

Nachum Ulanovsky: Yeah, no, no, it's a great, it's a great question. Indeed, it's not trivial at all. just to understand sort of the rationale, because this will come in in the story for a second, uh, the rationale for doing this study was that if We want to sort of, we did early on in 2010 2011, we did a study with GPS tracking of bats. 

We put Tiny GPS data loggers and tracked the navigation of bats outdoors just to be able to study and we found that they These Egyptian fruit bats have this very nice flyways where they fly from their cave to a particular fruit tree Night after night very precisely so they fly can fly 15 kilometers to the exact same fruit tree night after night So they are really good navigators if you look now at those flyways, what is the volume of the flyway? It could be You know, for example, if a particular animal flies, [00:28:00] let's say, 30 kilometers, so the length of the flyway is 30 kilometers, the width could be about 2 kilometers. So, like, the variability between days could be up to 2 kilometers. And then the altitude of variability is about half a kilometer. So we have, like, a sausage that's 30 kilometers long, 2 kilometers wide. half a kilometer high, that's about 30 cubic kilometers. That's the volume that you need to represent. And if you now want to take your 10 centimeter size place fields that you measure in small laboratory boxes and use those place fields to tile kilometers, then you can make the back of the envelope calculation, and you also want some overlap for robustness. It ends up being that you will need about 10 to the 15 neurons for that. So a million, billion neurons. Which is a lot more than what you have in the hippocampus, because the dorsal hippocampus you want, this particular area where place fields are found, is about 10 to the 5 neurons, or 100, 000 neurons in bats or rats. That's the order of magnitude, okay? Maybe two or three times more than that, but that's sort of the order of magnitude. So, [00:29:00] 10 to the 5, not 10 to the 15. So we had a gap of 10 orders of magnitude. This is an enormous gap. This means that what we, what we measure in small laboratory environments cannot translate to what's going on outdoors. 

Just impossible. There must be something else. This was sort of the rationale of how we came to do this study in the first place. But this was also the rationale of how I got this tunnel built. Because as you say, this tunnel, it was an. not underground, it's overground. It's more like a glorified tent, a long, very long tent, so to speak. Uh, a very robust one, but it's sort of a tent, tent's lightweight structure, like a greenhouse or a tent, if you will. And, and what happened is that I had, early on, I had this idea that, you know, it's very important to, uh, record in larger spaces if you're studying the new biology of navigation. How do you do that? 

There's no space for that in buildings, right? I went, uh, to the president, [00:30:00] president of the Weizmann Institute back then, Daniel Zeifman, and I gave them the spiel of why is it important. And the spiel was exactly what I just told you about this 10 order, orders of magnitude gap. And, you know, the, the president, he was a physicist, so he doesn't know much about the brain. But he knows about 10 orders of magnitude, so when you tell a physicist you have a problem that's 10 orders of magnitude large, he understands that very well. Okay, that's a big problem, this is something worthwhile pursuing. So after I gave him this spiel, and so he asked me, okay, so what exactly do you have in mind? 

What do you, how do you think to come about, you know, what you want to do exactly? I told him, I think the solution is to build a lightweight tunnel, like a long, lightweight construction. In some empty area, uh, on campus. And this was probably the moment that I had the highest heartbeat in my life. 

Benjamin James Kuper-Smith: [00:31:00] Yeah. 

Nachum Ulanovsky: me out. you know, what did I have to lose? So I gave him the spiel. I told him that's what I think we need to do. And, happily for me, he said, like, he rose up, and, you know, I was sitting in his office, and on the office of the president, there was this huge, like, the whole wall was covered by an aerial photo of the institute, like, you know, few meters in size. And he sort of stood up, came up to the, to this, uh, uh, photo, huge photo, and sort of looked at it and said, Okay, let's see, where do we have space? I like, yes! Um, so you know, when there is a will, there's a way, and you know, he did find space at the end of campus, which is also good because it's an area That nobody wants to build a building at the very far outskirts of campus, people, scientists want to be, you know, near their friends, near where the lectures are, near academic activities, so actually being five or seven minutes drive away at the very edge of [00:32:00] campus is very good, nobody wants this area. we do need to commute there, so we had to buy a golf cart, so we have a laboratory golf cart for, you know, taking, because the bats don't live there in the tunnel, they live in their lab, and we, for the experiments, we take them there, we do the experiment, and we drive back. So we have a golf cart for this driving, but, you know, this has ended up being a very convenient, uh, 

Benjamin James Kuper-Smith: Yeah, that's, that's an unusual, unusual bill for a neuroscience lab to have a 700 meter long tent and a golf cart. 

But hey, I guess. Um, but I mean, that's cool that, um, yeah, he allowed, he, he kind of saw the problem. And just kind of, I guess, trusted you that your solution also works for it, right? As you said, like, he could very, like, it seems like a more, right, the more defendable decision would be to say, Can't you just do, like, normal science? 

Like, do you have to do this? Um, [00:33:00] yeah, that's, it's pretty cool that he, that he did that. 

Nachum Ulanovsky: yeah, I totally agree. I think I really appreciate that. It's not obvious, but I think good managers, that's what the, you know, good science managers, that's what's supposed to need to, to trust their scientists. And just as long as it's feasible, just, you know, go with it. 

Benjamin James Kuper-Smith: And so then with the, with the 700 meter tunnel, it was, like, what do you gain from, from the extra 500 meters there in terms of, like, what kind of scientific questions can you answer that you couldn't do before? 

Nachum Ulanovsky: That was, I mean, we, with the bigger, the original tunnel was a sort of a quick construction. We did not have air conditioning. We did not have a lot of things. Now we sort of added, air conditioning which makes a big difference because if you're trying to run an experiment in a greenhouse in August in Israel, you know, good luck with that. 

So students ended up running experiments in the summer between 6 a. m. and 8 a. m. in the morning and then You know, starting at five in the afternoon and until midnight or sometimes even two in the [00:34:00] morning. So it was totally crazy hours. Actually, eight to five, which is the more normal working hours for most people, we could not run experiments in the summer because it was too hot. 

So now we actually can because it's air conditioning. This is like a practical thing. Also, we added. Some turns, so we have now an ability to have decision making, the bat has to decide whether to continue straight or turn right. We also built a very large flight maze, 60 by 35 meters, so you know, sort of, uh, almost a football field size maze, which is like a real proper maze where we can do complex navigation tasks and ask many questions that are to navigation, as opposed to flying back and forth in the tunnel, which is great for asking questions about the representation of space, but it's not really challenging navigation in any way, and whereas in the maze is challenging and interesting. 

So we've added a lot of components now with this new construction, uh, but the basic idea still remained the same. 

Benjamin James Kuper-Smith: Hmm. So how does, does this cost a lot [00:35:00] to build this stuff? I have, like, I have no idea, like, what even, like, order of magnitude we're 

talking about here. 

Nachum Ulanovsky: it's millions and it did require a, it did require a donor to, to give money for that. But again, it's, uh, you know, we did, we did found a donor that was very interesting and interested in that. So that, uh, ended up being, uh, being, uh, fine. 

Benjamin James Kuper-Smith: Yeah. Uh, you mentioned earlier something that surprised, uh, when you talked about the, kind of, the distances that, that the bats travel. And to some extent, the, was it 20 kilometers, 30 kilometers? I've forgotten now. 

Um, but the, that large distance to, to some extent, surprises me less than the 500 meters height. 

Yeah. What are they doing in 500 meters height? I mean, supposedly there's no cave there. There's no tree. There's no fly. Are there flies there? I don't think so, right? Or like, what are they doing that high? 

Nachum Ulanovsky: Right, so it's only, they fly high only during commuting. So when they, around the cave they fly low, when they're around the fruit trees where they [00:36:00] eat, they also fly low. But when they're doing these straight long distance commuting flights from point A to point B, they really go up high and fly very high. 

And I think the reason is because they're very visual animals. It's one thing that's important to mention, that although bats know, bats are about almost 25% of mammalian species. So there are about 1400 species of bats, uh, in the world. So about a quarter of mammals are bats and, and they all, they all see some see not so well, but some see very well. 

Our bat species have excellent vision, much better than, than, uh, rats are ized. So they're very visual. They also have the sense of the colocation and because they're so visual, when you fly high up. You can see far away, and it's better for navigation, and we've, in fact, in this GPS study that we've done, uh, some 12 or 13 years ago, we've done an experiment where we translocated the bats to the desert in Israel and released them inside this crater, inside [00:37:00] this deep makhtesh, this deep crater. where they, from which they could not see their familiar area, and then they sort of got lost. They were flying around and around and around until they flew higher up and could see their familiar area, and then they started flying straight. It was very clear that once they see their familiar area, they start flying straight. 

So they do rely on vision. Uh, for navigation. Probably they use also other senses, but the vision is very important for long distance navigation, and then when you're flying high up, you just see further. 

Benjamin James Kuper-Smith: Yeah, yeah I mean, I was wondering about that when, when you talked about these large distances and correct me if I'm wrong But echolocation needs something to bounce off of, Right, 

So like you, you're, you're very limited to, I don't know how many, how far that goes but you know, you can't, you know, you can look like 20 kilometers far or something depending on weather conditions, right? 

But Um 

Nachum Ulanovsky: you're right. Echolocation, when you're flying at an altitude of 500 meters, echolocation will not work. at all. The furthest that you can get echoes from is from a few tens of meters, [00:38:00] maybe 50 meters from the ground. But like at these altitudes, you don't get echoes from the ground at all. You might get an echo from another bat or something like that, but, but not from the ground. 

So it's basically useless for navigation to fly at such altitudes. And in fact, there have been experiments, a study in the 1960s, something that will not ethically will not be approved today, but where essentially looked at how bats, it was in the U. S., done in the U. S., in, in, in sectivorous bats, not in our species, but these bats fly relatively high when commuting, but they actually caught some bats and took out their eyes. 

Okay, so today it will not be approved, but in the 60s people did such experiments, and then they describe in this paper that the bats flew much lower, as if they were sort of palpating the ground with echolocation, because now they had to rely on echolocation to navigate. And so, yeah, if you use only equalocation, you have to fly low for this to be useful. 

Benjamin James Kuper-Smith: Yeah, and I guess you also then it's, I imagine like it's harder to, what's it to not see [00:39:00] the forest for the trees or whatever, right? Because you can only look at like the very short distance stuff. So you lose this kind of larger perspective to some extent. So I'd imagine it's, 

it also limits you in terms of like, yeah, not getting lost over large distances. 

Nachum Ulanovsky: Exactly. Yeah, you can't see far away landmarks like mountain ranges or the sea or cities or any of these far away things that are kilometers away. You can use vision for this, and we think the bats do use that, but, uh, with the collocation, it's all very local. It's a completely different mode of navigation. 

And that's something we have to recognize generally in neuroscience that animals have different, uh, different sensory systems, even the same animal, when it uses different sensory systems, its worldview is completely different. The same animal, the bat, what it can use in terms of information when it's using vision versus when it's using echolocation, it's a completely different thing. is something that, I think, by studying non standard animal species, [00:40:00] you become more aware of this, uh, diversity. 

Benjamin James Kuper-Smith: Yeah, I mean, I think you mentioned there's, there are some on your website, you have some links to some, some videos and like short documentaries about your lab. And I think in one of them, you mentioned this, that, um, you know, you can use these two different modalities of, uh, sensing the environment, let's just say, uh, with echolocation and vision and separate them and kind of see like, you know, how that changes their perception and their navigation, that kind of stuff. 

And obviously you can't do that in that's kind of also one of the main advantages of using bats. 

Nachum Ulanovsky: Right. Yeah, yeah. We've done some years ago a study where we asked how is the same space represented using vision versus echolocation. So we had bats, uh, uh, either like fly between two landing balls, either using echolocation alone. So in complete darkness, uh, we had to use night vision goggles to orient around. 

Or, uh, using vision only, and we blocked echolocation by transmitting [00:41:00] broadband sound through some speakers, and we add separate control to make sure that the noise itself did not have an effect, you know, what we've, and we also had ventilators to blow, uh, blow away any odor trails in mid air, if such, they do exist, so really to create a clean, this double dissociation between Vision alone versus echolocation alone. 

We worked hard to achieve this double association. And then what we found is that the same space is representing using two different, uh, maps. So place cells in the hippocampus represented space both using vision and using echolocation, but the locations of the place fields moved around, or in some neurons, they shut off or place fields appeared. 

So there was what's called a remapping, a new map or a different map between when you use vision alone versus when you use echolocation alone. And this goes against the original idea of the cognitive map was proposed to be an abstract concept, right? [00:42:00] If you have an abstract map of space, it shouldn't matter whether you use vision or echolocation. 

But in fact, if you think about it, when you navigate in daylight, or at night in the same space outdoors, things look pretty different. So, turns out that in the hippocampus, at least, the maps are different. Now, of course, there could be still an abstract map elsewhere, for example, in the internal cortex or somewhere else, but at least in the hippocampus, the map is not entirely abstract, but does depend on the sensory system. 

And this is something that we could do by using the bat as an animal model, but it was It's hard to ask the same question in rodents, for example, because they don't have two distal sensory systems like the bath do. 

Benjamin James Kuper-Smith: On this topic of, like, different species have different advantages, is there some species that you think is kind of being overlooked in spatial navigation? I don't know, something where you're like, Oh, I wish I could do this thing and that species could do it. I'm just curious whether, whether there is anything like that. 

Nachum Ulanovsky: Yeah, I think once one general, um, it's not this particularly [00:43:00] specific species, but the class of species, I would say that we are missing is migrating species. So there is work being done on understanding migration, but that's mostly at the behavioral level and a little bit people are looking in the brain, but it's more looking at magnetic magneto reception in birds, things like that, uh, not really looking at individual neurons, but, you know, migrating species are amazing. animals, because they, first of all, they fly thousands of kilometers. That's now a completely different scale. Our bats are non migratory, so they fly a few tens of kilometers. That's a lot compared to a lab, but it's much less than some of the amazing, uh, migrating species that can fly thousands of kilometers. 

By the way, there are some bat species that are migrating 2, 000 or 2, 500 kilometers, so Yeah, some mammals do that. Um, and you know, then there you could ask questions about navigation. Uh, first of all, how do you navigate such large distances in a precise way? Also about the timing. How does the animal [00:44:00] decide that, you know, today is my time to take off from Africa and to go to Europe or the other way around, right? 

I mean, these are, I think, fundamental questions that we have very little understanding how these things works in the brain. So I think this is a whole. domain that, that we have no knowledge about. So in terms of, I would say, the missing types of, of, of animals, it would be migrating animals. 

Benjamin James Kuper-Smith: Okay, that's, that requires a very long Very long tube, 

but yeah, um, I have, I have two kind of random questions about bats just from not really like from personal experience a little bit. Uh, I've just always wondered about, but, uh, don't know the answer. I'm curious whether you, whether you have to know it. 

So basically where I grew up, which is like on the, in Germany, on the border to Netherlands and Belgium, uh, there are bats. Um, I can't find out which species, because as you said, there are so many, so like even in Germany. There are like 30 species of bats or something, but one thing I always find it kind of interesting is that The way I the only way I really see them is like [00:45:00] I'll be walking along a road when it's dark then you come by a lamppost and then you see something flying around there and my Initial assumption is always like oh, it's you know some bird or whatever because bats are not like You you forget that they existed because you never see them and apart from that one situation But then you, when you, you know, you only see them like flying underneath the lamppost, I'm assuming. 

Getting some mosquito or something like that. You only see them for like half a second, but in that half a second, it's enough to realize that that thing that you thought was a bird flew really weirdly because they have this like, you know, much more angular way of flying. I don't know whether that's the right way to put it, but like. 

It's very obvious that it's not a bird, just from the way they're flying, so I'm just curious, like, why is the flight, the way that bats fly, so distinctive that I, as someone who's basically never seen a bat in my life, can immediately tell that that's not a bird, but a bat? 

Nachum Ulanovsky: So there are two basic answers here why [00:46:00] the flight of bats looks different. One is size, so a lot of the bat species are very small, a few grams  

Benjamin James Kuper-Smith: Yeah, they're pretty small. 

Nachum Ulanovsky: and the really small species actually fly almost like a large moth so it looks sort of erratic and it has to do just with their size so one thing and there are no birds almost no birds of this size right so so birds are generally bigger most of them so so this is one difference so bats are just a lot of them are very small so this is one answer. 

And the other answer is that their mechanism of, uh, of, uh, wing flapping is different from the birds. The birds have this joint that's different than in the bats. And, you know, there actually are people who are studying aerodynamics of flight in birds versus bats, and bats are different. They can achieve the same end goals. 

So there are Uh, bats, uh, that can hover in one location, very similar to  

Benjamin James Kuper-Smith: Really?  

Nachum Ulanovsky: yeah, for nectar feeding bats, for [00:47:00] example, can hover in one location to drink the nectar of flowers. the end result is similar, but the mechanics of, of the wing is quite different. So, uh, so that also explains why, why flight, uh, bats looks, looks different. Yeah, bats are, are, uh, are very varied. You, you, you're surprised by the fact that, that they eat nectar. But you know, there are a variety of, of species and variety of food, uh, foods that bats eat. You know, there are of course the insect eating bats, but there are the fruit bats, like the ones we are studying. There are nectar drinking bats, uh, you know, baobabs, for example, uh, pollinated by, by bats. Um, agave cactus in, in Mexico. pollinated exclusively by bats. You know, agave is used for tequila. So, we bat researchers, uh, always say, no bats, no tequila. So, uh, so bats pollinate some, some important, important plants. Uh, there are bats that, that hunt, uh, small [00:48:00] animals like frogs. There are bats that hunt fish underwater. Amazing bats in Central America that will detect a fish comes close to the surface of the water. It creates a circular ripples. They can't, of course, detect the fish itself, but they see, see in pr, in, uh, you know, quote unquote, see, they see with the colocation, the, the circle created by the fish, the ripples, and then they put their claws in the middle of the circle and take out the fish. 

Uh, so the bats that do that, and there are, then, there are of course the vampire bats, three species of bats in Central and South America that feed exclusively in blood. So they're really very diverse in, in, in what they eat. 

Benjamin James Kuper-Smith: Yeah, one thing that really surprised me just because I looked a bit more at bats before we started speaking, it's just these enormous bats. Uh, that really, they look scary. I'm glad I don't see one of those flying around. I think they are, I think those are fruit eating bats, but 

the ones that I saw, but yeah, they can get big. 

Nachum Ulanovsky: Yeah, some [00:49:00] of the bats, some of the bats live on some Pacific islands or in Australia or in other places can get to almost two meters in size, 180, uh, 180, 180 meters a week span. Our bats are actually from the same family, so small cousins of those fruit eating bats. Same family, different genus. 

Benjamin James Kuper-Smith: Okay, uh, so the other random question I had is that I guess I'm kind of curious, kind of, in part, where bats live. Because the one thing that's really surprising here is that, like, as I said, you don't really know that bats live here until you occasionally see them in the evening. And I have no idea where they live. 

I mean, do bats, you know, the stereotype, I guess, that they live in a cave, right, and hang from the ceiling. But, uh, do they also, I don't know, do they just live in trees? Or do they Some built nests or like because I'm Or could it be that these you know bats like you described actually live like 10 kilometers away or something and You know some small [00:50:00] cave somewhere 

Nachum Ulanovsky: No, it's a great question. Bats actually They are very, just like they are diverse in the food items that they eat, they're also very diverse in the type of where they, where they live. Uh, so there are, on one, uh, end, the bats that lives in caves, uh, there are many, many species that live in caves. But then there are bats that live in little rock crevices, or that live in tree hollows, you know, inside, inside hollow trees, or bats that live under a bark of trees, or even bats that create nests, uh, so to speak, uh, not exactly like bird nests, but there are, there are these tent building bats in, in Central America. will sort of chew on these big leaves, think of like banana, uh, leaves, but, but those sort of types of leaves that are very big, they can sort of chew on the, on the central stem of that to, to make them sort of fold and create a little tent. And then they would sleep underneath this, uh, tent, so But that, of course, will hold for [00:51:00] only a few days. 

Of course, if you live in a cave, you tend to live there for many years. Um, and then if you're creating those tents, you have to create a new one every few days. And by the way, I didn't mention, but bats also live very long. Unlike, you know, a mouse or a rat that is old at the age of one or two or three years, bats can live dozens of years. 

There is a bat species that's 10 grams. in size that, uh, was shown to live, uh, up to 47 years. There was one individual that was recaptured in the wild after 47 years. Our species live at least 25 years, we know that, maybe 30 years or more. So, uh, so they live very long lives. That also means that they have many years to learn the layout of the land and to learn to navigate very well in this area they're 

Benjamin James Kuper-Smith: He had no idea as you said exactly like I assumed that they'd live, you know, more or less like a rodent, uh, in terms of duration, but he had no idea. Yeah, it's still kind of, I'd [00:52:00] like to know where these bats live. I just, I don't know. Maybe I can find like some local, like 

Nachum Ulanovsky: Yeah, so it's hard to, it depends, it depends on the species. Some of the big brown bats, for example, that we, uh, that I worked on in my postdoc, they, nowadays, they love to roost in attics of people. Uh, it's a great place, uh, it's, uh, you know, people don't go to the attic for years sometimes. And so, uh, you know, it's a convenient place to live in, quiet and, and, you know, heated, protected. 

So, attics have become very popular amongst this bat species. So, you know, it really depends on the species. 

Benjamin James Kuper-Smith: Yeah, I'm always fascinated with, I mean, I grew up in a fairly rural area, but like how many, how much, you know, wildlife there is once you actually start paying attention to it, uh, even in places where you wouldn't assume it. 

Nachum Ulanovsky: Yeah. 

Benjamin James Kuper-Smith: this is specific to Wagrab, but like we even have like beavers. 

I didn't know we had beavers here until I suddenly like walked through this one area where there was like a river and suddenly you see all these like trees with, you know, the, the gnawed off stump of a tree. [00:53:00] Um, 

Nachum Ulanovsky: Yeah, we have actually, actually on the White Swan campus, we have quite a lot of wildlife because we have like a fence around the campus, so it's, and it's, you know, protected area. So, uh, you know, nobody bothers the animals and actually close to the tunnel. As I told you, this tunnel and maze that we have are at the end of campus and there was like a big. 

empty area there. It's like a little piece of, of wilderness, uh, so to speak. It's, I mean, it's close to a road essentially, but it's, people don't go there except us basically. So, so there are some jackals that live there. There are some foxes. Uh, there are some pretty rare bird species that you can see there right near our tunnel. 

It's pretty, it's pretty crazy. 

Benjamin James Kuper-Smith: yeah, it makes me just want to go and, you know, go a bit more into the forest and just Watch, just gonna just say that and see like all the stuff you can see there. Anyway, going back to kind of your research on bats, I guess one thing I want to talk about a little bit more is the social lives and the social aspects that you, social lives of bats and the social aspects that you studied.[00:54:00]  

Maybe to kind of start that conversation again. Huge difference between different species of bats, but maybe for the egyptian fruit bats kind of what is their social structure do they um I I saw God, I mean, this is a different species, but there's this one like cave in the us where there's like millions of bats It's crazy video, but kind of what's the social structure of those bats that you use do they you know? 

live in large, uh, flocks? Is that the word? I don't know. Um, or yeah, kind of, what's that like? 

Nachum Ulanovsky: So they live that are not, not millions, uh, but between a few tens and a few thousands, that's sort of the typical size for the, for this species. It actually, again, varies a lot between different species. There are bat species that are solitary, that live alone. There are bat species on the other extreme. There's a Brazilian free tailed bats in Texas and New Mexico that you've probably seen videos of that have millions. of [00:55:00] bats in one cave, and then there are all sorts of things in between, so different species differ a lot in the numbers and in the social structure. Embarrassingly enough, we don't know a lot about the social structure of our bats. 

We know, I mean, it's not a pair structure, like pair bonding for life. It's more of a fluid thing, and they have a hierarchy. They have dominant males and females, less dominant ones, so likely the more dominant ones are the ones reproducing, but exactly the details of the structure. We don't know that much, but it's, it's sort of a dominant, uh, uh, type of, uh, of, uh, structure. 

Benjamin James Kuper-Smith: Do they, do they have, do they form friendships? Do you know anything about that? Like, where you realize, oh, those two are always hanging out together or? 

Nachum Ulanovsky: yeah, they do. And actually we've we've looked at that in a recent study. They have preferences for interact, you know, with particular bats and not with others. Um, and you know, some of the reasons that we went to to look at social aspects have to do with the [00:56:00] actually the representation of space, but some have to do with the social questions per se. So it started from like, again, several directions. We were looking at representation of space and neurobiology of navigation. But then, you know, one of the things you need to do is to train bats to do all sorts of tasks. And one of the things that we found very quickly is that Uh, if you use one animal as a teacher, you find one animal that does the task, whatever the task is, does the task very well and just let it perform the tasks while other bats watch it, they learn the task much faster than from a human. 

So a bat trainer is much better than a human trainer. And observational learning going on, much more than in rodents. And so this was, for many years we used it as a, training trick, but then we actually at some point realized that this is an interesting question in its own right, scientifically. Uh, the other reason is that we studied the hippocampus, this brain area where you have place cells, neurons represent where I am in space. [00:57:00] But then for such a highly social species, you can ask, are there also neurons in the hippocampus that represent where you are in space, where another individual is in space? So this was a study that, uh, the first study that we did on the social aspect looked exactly at this question. We, you know, we, we did a, a, a task which involved two bats. 

A, a teacher or a demonstrator and an observer bat, a student, so to speak. And this was a mimicry task. The observer had to mimic the, the behavior of the, of the demonstrator mostly to, so that it would pay attention to the position of the other bat. This was the main rational here, and what we found is that wild. The bat itself, the recorded bat was flying. We found we would see play cells, normal looking play cells. You know, when I'm moving to space, I have neurons in my hippocampus that are active in a particular, when I'm in a particular location in space. But when I was resting and you were flying, so the other bat was flying, we found that there are neurons that are, were activating whenever the other [00:58:00] bat flew through a particular location in space. 

So I'm not moving at all. And we had actually a motion sensor on the head on accelerometer. to verify that the recorded bat was not moving at all and was just watching the other bat. And still, the neurons in the hippocampus represent the position of the other bat. And we call these neurons social place cells. And, you know, we add all sorts of controls to show it can't be explained by all sorts of other explanations, and, uh, and that it's sort of, it's, it's, there was a social aspect here because we also moved plastic objects to space, and the neurons responded differently to the real bat than to the plastic objects, so there to be something really social here. 

So we call these neurons social place cells. Neurons represent the position of another individual, which is, of course, uh, uh, Very important for all social animals to know where, where are, is somebody else is very important. You know, I, my kids are, are grown up now, but when they were little, you would go to the park and you always pay attention, you know, where's the little kid who doesn't run to the street or something, you know, or where is your spouse [00:59:00] and, uh, or your friends in the bar or whatever. 

So paying attention to the positions of other individuals is important or in any. Sports games like football, basketball, things like that, the really good players are ones that, of course, in addition to the physical sides of things, but the really good players are very good at keeping track of where are the other players on their team and the other team, so this ability to track the positions of other individuals is very important for social animals, and these are Social play cells might be related to that. 

And then after, after that, we, uh, we sort of asked, uh, the next question and sort of an obvious question, which is instead of having just one other. What happens if we have multiple animals? How do you represent them? And, uh, so we, we, we created this, uh, so with the first study was already published in a few years ago in science, and what I'm going to tell you now is an unpublished study that we're just, just submitted. 

And what we are, where we are seeing is [01:00:00] that when we create this colony of bats in the lab, so sort of a group of bats and we develop methods to track the positions and identities of all the, uh, all the bats in the group. Groups of about five to ten bats. We found that there are neurons that represent, uh, the positions of all these other individuals, but they also represent not just the the positions, but they also represent, uh, you know, we're sensitive to presence or absence of another bat and also to the identity of another individual. 

Is it one bat or another bat that's in a particular location? also these neurons represented the other features of the kind of important social features like the sex that responded differently to males versus females, they responded differently to depending on the dominance hierarchies at the bad high in hierarchy versus low in hierarchy, and also they responded differently to are you my friend or are you not my friend. 

And we saw when you track behaviorally In this colony we see that they have preferences. You can identify who is my [01:01:00] friend because, you know, they tend to interact with one individual more than with another. And so, and this is, these preferences are stable over many weeks, so it's really sort of friendships, if you will. And, and these friendships were represented by the neurons. So there's a lot of very strong social signals that, that we see in the hippocampus, uh, in this highly social group situation. 

Benjamin James Kuper-Smith: I'm especially wondering like, as you said, like, if you have like multiple other people or bats or whatever in the same room, do they track all of them or just the kind of? ones that are relevant for a particular task or that kind of thing, because I don't know I'm curious like especially what you mentioned For example with people like the example football if you know if you're a midfielder, you might have like 10 people around you, right? 

Yeah I would imagine it's difficult to keep track of all of them and where all of them exactly are moving as as Individuals and that kind of stuff. So I'm curious whether you especially those that you know, maybe aren't relevant for what you're trying to do So I'm just curious whether [01:02:00] there's Whether you differentiated there between the, how, how relevant kind of a particular bat was for a particular task. 

Nachum Ulanovsky: Yeah, so that's a great question. Um, in this experiment that we did recently with a five, between five to 10 baths, we found that neurons did tend to represent the individual. So not all neurons, some neurons tended to generalize across individuals, only representing a few of the individuals, but, but some of the neurons represented the individual. all the various different individuals. So if you combine all the neurons together, you can tell apart whether, you know, which individual is that. But that's for a relatively small group of five to ten animals. What happens if you go to a whole colony of thousands of animals or to those, those, uh, colonies, uh, uh, with, uh, Brazilian free tailed bats where you have millions. 

I mean, you don't even know millions of people, right? How do, you can't represent them individually. So, so I agree with you that it doesn't make sense that, that all individuals are represented. It's probably by relevance. So if you go to a full colony [01:03:00] of bats, I think, and, but this is an open question, it's something that needs to be done, you know, with much larger groups, is that, you know, either you'd represent just the, let's say, most animals, like the high animals highest in the hierarchy, for example, or the ones most relevant. 

For example, the ones closest to you, you don't care about the ones far away, only the ones closest to you, or the ones that are on collision course with you, or other criteria of relevance, but I agree with you that that's the most likely situation. I don't think that it makes sense for the brain to represent 10, 000 animals simultaneously. 

I don't think it's feasible and, and, uh, and probably that doesn't happen, but it's an open question to show that it's a different thing. 

Benjamin James Kuper-Smith: Yeah, I mean, I guess some of it I assume would happen also at the, at the sensory level. Like if you, I was just thinking like if you enter a subway or something like that, um, as in underground tube, not food place, um, then I guess even in the food place, [01:04:00] um, you know, there are maybe some people who are sitting like five meters away from you at a bench. 

You probably don't even. Perceive them, but I guess the closer they are to you and that kind of stuff you perceive them And then there's some people you ignore anyway, but yeah, I don't know I guess it 

Nachum Ulanovsky: and I think, I think, uh, that's another reason why we need to move to larger spaces for neuroscience research, right? So it's maybe not the most important reason, but what you just said is that in a large enough space, I care about the individuals close to me and not far away. But if you only do experiments in very small spaces, then all individuals are close to you, so you think that the neurons care about everybody. 

In this particular experiment, It was a relatively small space, it was a room of about three by three meters in size, and, and, you know, when most of our analysis were done, were done when the animals were really close to each other, so everybody is relevant. But you're right, that in a very large space, this could be very different, so I think for that you need to do the experiment in a large, in the large space. 

So, just like it's important, to go to large spaces to study the neurobiology of [01:05:00] navigation, even for social questions, it's important to go to large spaces, not maybe 700 meters, but larger than normal. 

Benjamin James Kuper-Smith: Yeah, I have kind of one fairly general spatial navigation question, which especially to me And yeah, it's, it's kind of a question I have increasingly when I kind of read new studies. The question is kind of like what to make of there being so many different cells, you know, place cells, grid cells, that kind of stuff. 

And that so many of them are modulated by so many kind of contextual factors. And kind of what I mean by that is that, you know, when you start off, you know, learning about this stuff, you know, you learn here's place cells and there's grid cells, head direction cells, and then, you know, you get to border cells and all that kind of stuff. 

And it's just, It just increases, right? You just learn like every, it seems like, you know, every other paper in special negation has a new type of cell and I'm not entirely sure what to make of that, but at some point I wonder, like, is this a sign that we actually don't understand the underlying principles or is it just. 

What happens [01:06:00] naturally if you have animals or people moving in complex environments that you, you know, you need to take into account all the complexities of the environment. Um, I'm just curious whether, whether you could kind of comment on that because, yeah, it's just something I'm increasingly wondering about without really knowing exactly kind of what my question is there. 

Nachum Ulanovsky: No, that's a great question, but I think actually it's two different questions that are involved there. One is the issue of are there distinct cell types, because we In simple environments, we tend to see these simple neurons, grid cells, place cells, head direction cells, et cetera, and we tend to classify them. And in more complex environments, things become more complicated. For example, what I told you about this long tunnel where a neuron, a place cell in the hippocampus has multiple place fields, that starts to sound a little bit not so different than grid cells, that also multiple place fields are maybe more periodic. 

But, you know, so things become too become, uh, more, uh, uh, [01:07:00] a little bit less distinct, uh, when you go to more naturalistic situations. So the question of, is there a really distinct sense of set, set of neurons, or is it more of a continuum? I think it's an open question. Uh, there is some evidence that grid cells maybe are a distinct set of neurons, That's also an open question, I think, but for a lot of the other cell types, I think we need to understand, do you have complete mixed selectivity, where all neurons represent sort of everything, and when you go to very Uh, simple abortive setups, then you end up seeing the extremes that, uh, neurons represent, this or that, and then you categorize them into cell classes, but maybe in more naturalistic situations, things are more of a continuum. 

This is sort of one question about cell classes. The other, and very related question, is about naturalistic or natural environments. Because for the same type of cell, if you, what we have been showing over the years, is that [01:08:00] we, for the same type of cell, when you introduce more naturalistic aspects, you find, uh, that they're, have more complex responses. So when we looked at three dimensions, we We found 3D place cells neurons that represent the three dimensional position of the animal, we found 3D grid cells that we didn't talk about them yet, but unlike the two dimensional grid cells that have this hexagonal pattern of activity in space, in three dimensions they have a local distance metric. between their grid fields, but not a global lattice. So this is sort of quite different, the grid cells look quite different in three dimensions than in two dimensions, which have important implications for, for theories of grid cells. Uh, we looked at 3D head direction cells, we found these interesting properties, the, uh, we, we did find 3D compasses, the 3D head direction cells, but they were represented on a toroidal reference frame, not in a spherical reference frame. 

So some interesting findings there. Then when we introduced a navigational goal, of, uh, looking at where [01:09:00] I am in space to look at how is the goal represented in the brain, we found that, uh, we found vectors in the brain. We found neurons in the hippocampus that represent the egocentric direction and distance to the goal. 

So literally a vector to the goal, which is a very useful for, uh, for navigating to goals, so a very different type of representation than place cells. Then when we introduced animals, other animals, as I told you, we, we found those, uh, social place cells, neurons that represent the positions of other individuals and, and, and sex and dominance hierarchy and affiliation, et cetera, a lot of very strong social signals. 

And when we increase the environment size, we found, you know, all hell breaks loose, we find this multi field multi scale type of code. So every time we take a step into a more naturalistic direction. We found something complex and interesting about the brain. First of all, I think it's really, shows that it's important to study the brain under more natural conditions. 

And I'm now actually [01:10:00] finishing writing a book for MIT Press called Natural Neuroscience. Um, I'm submitting the final version of the book, uh, actually in a few weeks, so it's almost done. And, uh, and the idea of the book is exactly to talk about why is it important to study the brain under natural conditions. Another aspect of your question is, is everything represented in the neurons? So like, is anything that you throw at the neuron, the neural represent? And I think the answer is not everything, but, but maybe in the hippocampus of these, the answer is that everything that's relevant. And the reason I'm saying this is because, as I just told you, we have the, we have these social places, neurons that represent the position of other individuals in a social situation. 

Okay. But we also did an experiment in the tunnel where we had two bats flying opposite each other. This was a, you know, paper in Nature, uh, last year. And what we found there is that as, you know, when the bat is flying alone, it's representing its own position with this multi field, multi [01:11:00] scale code that I told you about. 

But when they are flying opposite each other, they are switching between representing my own position. to representing the position and the distance to the other bath. And when they're passing each other, the neurons are going back to representing just my own position. So there's like this switch from representing my own position to representing position and distance, and then back to representing my own position. 

So this was sort of the reason to do this study, it was to look at how very dynamic type of behavior, or when you switch behavior from navigation to collision avoidance, how does that affect the neural code? And the answer is that it affects the neural code dramatically. Neural code is very dynamic when the behavior changes dramatically. But one interesting aspect of that study is that we did a variation of the experiment where instead of having one other animal, We actually switched the other animal. So instead of bat A flying opposite bat B, we had bat A flying opposite bat B or bat C. So we can now compare what happens when bat B or bat C is [01:12:00] flying opposite me. 

And it turned out that there was actually no difference. The neurons switched to representing the other bat in exactly the same way. It didn't matter if the other bat was bat B or bat C. But it actually makes sense, because this is not a social situation. It's a collision avoidance, you know, when you're driving on a road, and you're about to collide with another car, you don't care if it's, you know, this car or the other car, you just mostly care getting the hell out of there and not colliding, right? 

So it's not a social question, and indeed, the identity in this condition was not represented, whereas in the more social situation, the bat identity Was represented because it was relevant a social situation, bad identity is relevant. In the collisional avoidance situation, bad identity is irrelevant, and then it's not represented in the neurons. 

So I really think, and we have several other examples like this, where if something is relevant, it's represented, but if it's irrelevant, it's not represented by the neurons. 

Benjamin James Kuper-Smith: I know you didn't call them collision avoidance cells, but I think that would be a nice addition to the [01:13:00] list of cells. Yeah, it's funny. I wanted to ask you a little bit about how, how the natural neuroscience book is going because you, uh, I saw, uh, on, on YouTube, I saw a talk you gave a couple of years ago. 

So you mentioned you were writing it. So I was like, how's it going? So, but I guess it's, it's, it's progressed quite a lot then if you're about to submit, uh, do you want to say a little bit more kind of about this? I think in the same talk you talked about a kind of slightly false dichotomy of controlled but unnatural and versus controlled but natural. 

Yeah, do you want to maybe want to elaborate on that point? 

Nachum Ulanovsky: Yeah, I think it's, uh, sort of the, the main point of the, of the, the book, the natural neuroscience book, is about the importance of going to more naturalistic behaviors. And the, the basic idea is that. We have experiments, typical experiments in the lab, especially in the olden days, have been very controlled, but also very unnatural. 

And I always fear that if you do very unnatural experiments, especially on the neural base of behavior, it's a problem, because we might be missing important aspects of what the brain is doing. We [01:14:00] don't really let the brain do its normal thing. On the other extreme, you can do something that's completely uncontrolled, but completely natural, and that's hard. hard to analyze, uh, it's not, it's, it's, it's not, uh, a lost cause because often if you let animals do whatever they want, they will still do some behaviors repeatedly. Like in our colony situation, they would fight over and over, they would food over and over, you know, they would It repeats certain behaviors over and over so you can still align your neural activity on these repeating behaviors and see how the responses look like. 

And it's not a completely random behavior. So even if you don't have any task and you let animal do their completely natural behavior, you can make sense of the data. And we are showing that with our, with our, uh, studies. But is my point is that it's it's important to have a diversity. So between the one extreme of having highly controlled but highly unnatural studies and the other extreme [01:15:00] of highly uncontrolled, but, uh, but natural studies, you first of all, we I think we as neuroscientists need to cover the entire range. 

And the other point is that as you as you said, is it's actually a false dichotomy because it's more of a two dimensional axis. You have an axis of control. Control versus uncontrolled and you have access of natural versus unnatural and you can have also situations where you have a controlled but natural behaviors or behaviors that are highly repeatable, highly reproducible, but also highly natural. 

For example, birdsong or the hunting sequence of the bat or hunting. uh, many other, like escape of a cockroach or many other behaviors that are done relatively stereotypically by animals. And so they're very amenable to study, but they are very natural. So I think those are the type of behaviors that are particularly important that we'll look at as neuroscientists. 

Benjamin James Kuper-Smith: Yeah, I'm just kind of curious on [01:16:00] the topic of natural neuroscience that kind of stuff What are you kind of what you want to do next? Do you have like a big a big new project that you know Advanced this to a whole new level or kind of I'm just curious kind of how it sounds like you've been thinking about this quite a lot Kind of what you want to do next and kind of making these more natural tasks 

Nachum Ulanovsky: First of all, I think we are going in my lab to more and more naturalistic experiments. So, uh, you know, the social side, you know, groups of animals, more and more natural interactions. Also, the technological development helps a lot in that because we are developing, the neurologers that we have been developing, they are becoming smaller and smaller. 

So it's easier and easier for the animals to carry them. So all of this helps a lot with the We're on the practical side of the experiments, uh, more complex and naturalistic and navigation. I think down the road, it will be very interesting to look at, study the brain outdoors. There'll be, there'll be sort of a dream, [01:17:00] a dream experiment. 

And generally I would say we are moving more and more into a more natural experiment while still maintaining. control and reproducibility. So it's very important to stress we're not doing, you know, experiments where animals are doing random stuff. We are, you know, we do have them repeat some behaviors, do some, some, some control manipulations, but have the experiments in, in the more naturalistic situation than normally done in laboratory studies. 

Benjamin James Kuper-Smith: So yeah, at the end of each interview, I asked my guests the same kind of three questions. Uh, the first is, what's a book or paper you think more people should read? This can be famous, uh, completely unknown, old, new, just something you think more people should read. 

Nachum Ulanovsky: It's not a particular paper, but I think the old papers I would highly recommend. I remember to this day when I was a PhD student, I took this course about reading these old papers. So by [01:18:00] old, I mean, uh, Hodgkin and Huxley, Hubel and Wiesel, the magical number seven plus or minus two, Uh, you know, What the Frog's, uh, Eye Tells the Frog's Brain. 

All those classical papers from the 50s and 60s, of all, they are a joy to read. Uh, you know, you learn about them in courses, but to read the original is really interesting. They're written in completely different language and in a completely different way than, than things that are written, uh, nowadays. 

And it's, uh, it's very interesting. Like, you know, you read Hodgkin and Huxley, and in one of their papers, they, you know, pages, literally, uh, sort of, uh, uh, asking the reader's forgiveness for the fact that they did the experiment, uh, not in body temperature, but in room temperature, and what would that entail, because of course, all the kinetics could be, is, is very much temperature dependent, so, you know, but they literally spent like two or three pages, uh, you know, uh, saying, [01:19:00] well, it's problematic, and we're sorry, and we haven't seen it, it's like, where would you see in any paper today, somebody full two printed pages, you know, acknowledging a problem like that. 

I mean, this is really amazing to read. So I, I would. I would tell students, go read original classics, it's just interesting, you know, if you won't learn anything beyond the, what's written in the textbook, you'll just learn about a different style of research and about how to write things, it's, uh, you know, these people got Nobel Prizes for good reasons and it's highly recommended to read those original papers. 

Benjamin James Kuper-Smith: yeah, the, the writing style, how that changed over the years, I was, I found it quite interesting too. I mean, I haven't, I haven't read any of the specific ones you mentioned, uh, but I remember once I just kind of, I can't remember why, but for some reason I was just like. I wonder what the, the, the paper [01:20:00] is, uh, like where Turing wrote about the Turing test, right? 

Where he like wrote about that. And so I just like randomly found it and then, uh, started, I think I read the first few pages and what really surprised me was that, you know, this was a computer scientist or mathematician writing kind of philosophy. And I thought it was going to be like super complicated and technical, but like the first two, three pages that I read were just So easy to read, like it was so clearly and yeah, clearly written. 

I was really amazed by it. Yeah, it makes me wonder sometimes Why exactly some of that got lost. 

Nachum Ulanovsky: Yeah, I totally agree. 

Benjamin James Kuper-Smith: Uh, final question is Advice for PhD students and postdocs So kind of people on that transition any advice you tell them 

Nachum Ulanovsky: Yes, I think one advice is to find, find your own way, find your own niche. I mean, I. I did it when I switched to the bat and it [01:21:00] proved very successful. If you're looking for doing something that is different from others, it's often an advantage. It's easy to look at what everybody are doing and say, I want to do the same thing. 

It seems to work, you know, everybody are doing mice, optogenetics, whatever nowadays. So, but you know, there are thousands of people like you and um, And actually doing something different on could be a different species could be a different question, a different brain area. Something different stands out. 

And, you know, I actually that's that's that's very important. On the other hand, it's also important not to go to something very esoteric. I mean, I love, for example, Uh, neurotology where people look at particular, uh, interesting critters, uh, but some of the, of the animals that, that people study there are just not, you know, most, most neuroscientists don't care about this. 

So if you are a neurotologist, if you want to understand particular species, [01:22:00] great, go for it. But if you. want to stay closer to the mainstream of neuroscience, and I would say trying to find a species or a question which many researchers would find the research interesting. For example, you know, my study in the bats, although I study a highly unusual species, on the other hand, The brain area that I study, the hippocampus, is extremely, uh, uh, well studied. 

It's the second most studied brain area of all, so there's a lot of labs interested in that. 

Benjamin James Kuper-Smith: Wait, what's the first? 

Nachum Ulanovsky: well, neocortex, I would say, if 

Benjamin James Kuper-Smith: Oh, okay. 

Nachum Ulanovsky: did a search at SFN, many abstracts have, uh, you know, hippocampus or hippocampal in the, in the, you know, tidal or abstract. This was many years ago, but there were 3, 500 posters at that SFN with hippocampus or hippocampal in the, you know, in the abstract. 

That's a lot. only, only Cortex had more. So, so it's a highly studied area and And then people are interested in that. So I would say general advice, if you can find a [01:23:00] species or a question or a direction that is unique on one hand, but does relate to the mainstream of neuroscience, that's the best place to be in. 

Because then automatically what you do is unique but is relevant and interesting for a lot of people. And then, you know, there's no problem, you know, people are interested and want to hear what you have to say. And then there's no problem to publish, no problem to get funding, uh, et cetera. So this is sort of the sweet spot that I would advise people to look for. 

The unique but relevant sweet spot. 

Benjamin James Kuper-Smith: Yeah, because I was, I was wondering as you, as you started, I was wondering like how do you, you know, to some extent, uh, your career could be one side of a survivor bias, right? Where let's say lots of other people tried something in similar studies and it just didn't work out and we don't hear about them because it never did anything interesting. 

And there's this one. Uh, video, I think, from The Onion, which is fantastic, where they have this like, you know, obviously satirical interview with someone who studied anteaters all his life. [01:24:00] And they're like, oh, tell me about anteaters. And the guy's just like, no, they're just boring. There's nothing interesting. 

I wasted my entire career on them. I just has this like existential crisis 

on TV about like, no, it was just pointless. Like I hate anteaters. I don't know why I did it. Right. And, um, but so to avoid that you think it's kind of connecting it to a mainstream thing that does address kind of fundamental questions. 

Nachum Ulanovsky: I think, especially if you're interested in general questions about the brain, in general neuroscience, that's the way to go. If you're a more etologist or neurotologist at heart, and you just, you want to understand a particular critter for its own right, great, go for it. It's, it's just that you need to be aware that If you are studying a very esoteric species or a very esoteric question that does not relate to most of neuroscience, then you're going to remain in this niche and not break through to the mainstream. 

So it's sort of, you know, it's, it's, it's an approach, it's an attitudinal approach. If you want to do that and [01:25:00] study anteaters or whatever, great. I mean, I love that. As I said, I grew up as a kid watching nature documentaries. When I hear talks about a, an esoteric species I've never heard before, it always amazes me. 

I love, I love that stuff, but it really puts you away from mainstream neuroscience. If you want to remain closer to mainstream neuroscience and, and ask questions that are relevant for the broader community, then you, you need to make this connection. So this is sort of. a tension here, but it's doable, you know, my research shows that it's possible. 

There are other people who are doing that. So, you know, it's, you can find this niches that are unique, but on the other hand, also relevant for the general neuroscience community. I think that's a great place to be in because then, you know, you're automatically, uh, you're interesting for people. What you're doing is interesting for people. 

Benjamin James Kuper-Smith: Yeah, definitely. Okay. Well with that, thank you very much. 

Nachum Ulanovsky: Thank you so much. Thank you.

How Nachum started working with bats
The technical difficulties of working with bats and in a new species
The Egyptian Fruit Bat
Wild bats vs lab-born bats / spatial navigation in very large spaces
How to build a 700m long tunnel for neuroscience
2 random questions about bats
The social lives of bats & social place cells
Why are there so many types of cells for spatial navigation?
Natural neuroscience
A book or paper more people should read
Advice for PhD students/postdocs