Think Out Loud

University of Oregon research offers a window into how octopuses see

By Gemma DiCarlo (OPB)
Aug. 2, 2023 7:15 p.m.

Broadcast: Thursday, Aug. 3

While there are similarities between human and octopus eyes, new research from the University of Oregon shows the way our brains process vision is completely different. (FILE)

While there are similarities between human and octopus eyes, new research from the University of Oregon shows the way our brains process vision is completely different. (FILE)

Stephani Gordon / OPB


Research shows that up to 50% of the human brain is involved in visual processing. For octopuses, that number is roughly 70%. There are similarities between octopus and human eyes — both involve a lens and a pupil that allows light into the back of the eye — but the way our brains process vision is completely different.

University of Oregon biology professor Cris Niell has been studying these processes in his lab. The team recently published a paper in Current Biology on the ways octopuses organize visual information in their brains. He joins us to offer some insight into how octopuses see.

The following transcript was created by a computer and edited by a volunteer:

Dave Miller: From the Gert Boyle studio at OPB, this is Think Out Loud. I’m Dave Miller. About half of the human brain is involved in visual processing. For octopuses, that number is more like 70%. And while there are physical similarities between octopus and human eyes, the ways our brains process vision are completely different. The University of Oregon biology professor Cris Niell has been studying octopus vision in his lab. He joins us now to talk about his work. Welcome to the show.

Cris Niell: Thank you very much.

Miller: Before we even talk about your research, am I supposed to say octopi or octopuses?

Niell: Yeah, this is a good one. Actually the common plural is octopuses. Octopi is actually incorrect because that’s putting a Latin suffix onto a Greek word, a word of Greek origin. If you’re really going to be technically correct, it would be octapodes, but nobody actually says that.

Miller: So technically correct, and as you speak Greek.

Niell: Exactly.

Miller: OK. Well, we’ll stick with the English and I’ll say octopuses.

Niell: It is hard not to say octopi though, it’s very natural.

Miller: I’ll do my best. So in your lab, my understanding is you’ve in the past focused a lot on mice, including studies involving hallucinogens, that got a lot of press a couple of years ago. How did octopuses enter the picture?

Niell: Yeah. So we’ve been studying mice for quite a while because their visual system is actually in many ways similar to ours. They’re mammals, actually, evolutionarily, relatively closely related to us. They have all the same parts of the brain that we do, the thalamus, visual cortex, and so on. So they’re actually a great model for being able to understand our visual system based on those similarities. They’re a common lab species. So, they make a good system for studying our visual system.

On the other hand, octopuses are completely different and that’s actually what got us interested in that. In fact, our entry into octopuses was a little bit serendipitous. I was contacted about a number of years ago by a then graduate student named Judit Pungor, who had been studying the anatomy of the octopus visual system. And she wanted to try and figure out if there’s a way, can we look inside their brain and figure out what these neurons are doing? Can we watch them in action? And when she brought that question to me, I got immediately hooked.

I hadn’t really thought about studying octopuses before. But I read a little bit up on what was known, as you mentioned in the beginning, they have eyes that are remarkably similar to ours. Kind of one of these remarkable facts of evolution. Our common ancestor was probably a small worm, but something that didn’t actually have eyes and somehow evolution separately came up with the solution of an eye with a lens and a pupil, and so on. But then beyond that, their brain is completely different. Their branch of the animal kingdom includes some slugs and snails, and so their brain is almost kind of like a giant slug brain. And so everything after that looks different, as I mentioned for the mouse, they have the same brain regions we do, things like the thalamus and cortex, none of that’s there in the octopus. You just look at its brain and it almost looks like an alien type brain with all these different lobes. Nothing that looks familiar.

Miller: And I wanna get more into that in a second but just in terms of becoming a lab that also studies octopuses, I mean, how common are octopuses in lab settings?

Niell: It’s starting to grow. In fact, a number of the early findings in neuroscience were based at marine stations that studied species like squids and octopuses, because you take them out of the water and look in their brains, but it kind of died down over the past several decades, really because there was a big focus in biomedical research on a few species that were standards that everybody studied, things like zebrafish and mouse. And so some of these more exotic species kind of fell by the wayside. And there had always been a kind of a small core group, I would say maybe 5 or 10 labs around the world that were working on it.

Over the past five years or so, I’d say there’s been a real kind of a renaissance in the study of cephalopods. In fact, we’re putting together the first ever cephalopod neuroscience meeting and we have something on the order of about 25 labs that are now working on either octopus, squids or cuttlefish. And a lot of that’s due to the fact that there’s this renewed interest in the breadth of the animal kingdom as opposed to focusing in on just a few species.

Miller: How much was previously known about the vision of octopuses and what were the particular gaps that you wanted to help fill in?

Niell: People had done studies looking at the structure of their brain, looking at which neurons are connected to which neurons, which parts of the brain are involved in vision, versus learning, versus controlling camouflage. But there had never been the opportunity to look inside the brain and see what these neurons are doing. It’s kind of like if you could look at a computer and you could say, ah, I can see all the parts and I can see the wires between them. But really what you’d like to do is go in there with a voltmeter, so you could measure the signals that are being sent from the CPU to the memory and so on in order to be able to actually figure out how it works.

Miller: And how were you able to actually get inside the brain?

Niell: So we used microscopy techniques that allowed us to look through the brain. We put in a fluorescent dye that we can inject. It goes into the brain, lights up the neurons and is kind of like an FMRI. It causes those neurons to light up more when they’re active. And so then we can put the octopus in a little chamber. They’re looking at a computer screen where we’re presenting it, they’re underwater, but they’re looking at a little computer screen on the side of their chamber. We can play different patterns on that screen and then we can look and see how the brain responds, again much like putting a human in an FMRI.

Miller: So what kinds of things were the octopuses looking at on the screen?

Niell: It wasn’t very exciting. Mostly it was spots at different locations, and that’s the reason, because a couple of the things that we wanted to look at were how the brain responds, first of all, to objects at different locations in front of it and how it responded to light versus dark. . .

Miller: Why are those obvious choices to test or to better understand their vision?

Niell: So in humans, and in fact, almost all mammals and in fact, almost all vertebrates, the visual system is organized to represent the world in front of you. So you might have seen diagrams, if you look out at a tree, that image of the tree gets flipped upside down in your retina and then gets flipped back up again when it goes into your brain. So there’s almost like, within the visual part of our brain there’s what we call a visual map, that is basically an orderly representation of what you’re seeing out in front of you on the surface of the brain. And we wanted to figure out whether that was true in the octopus as well. And part of the reason we were interested in that is because other parts of our brain are organized similarly. So for example, there’s a map in your brain of your body. So where, in your sensory cortex, your hand is next to your arm, next to your shoulder.


That doesn’t seem to be true in the octopus, that their representation of their arms and their body is all kind of jumbled up and suggested that maybe because they’re so different than us, they’re just organizing their brain differently.

What we found is in the visual system, it’s actually quite similar to vertebrates. We found that same orderly map. So if we presented a spot on the left side of the screen, it would activate the left side of the visual part of their brain. And if we put it on the right side of the screen, it activated the right side of that brain region. So there was that similar type of visual map, the same similar organization, which to me was, on the one hand makes sense, that’s an obvious way to organize your brain. You want to keep things that are nearby in the world nearby in your brain. But, it’s possible that things could be totally different just because they are so different in their evolution.

Miller: What surprised you most in your findings?

Niell: Things got a little bit different when we started looking at the responses to light and dark spots. And so in humans, basically starting right after the photoreceptors, the visual system takes light coming in and processes both light and dark, similarly. It puts them into two separate pathways, but treats them essentially the same. We found those two same pathways, a pathway for light objects and for dark objects, but the responses in those two pathways were actually quite different. In the pathway for light objects, they tended to respond to small spots, and the pathway for dark objects, they tended to respond to large spots. And to us that was kind of surprising. For us, we treat these, our brain treats light and dark relatively similarly. Here, they’re being treated quite differently. But it actually makes sense in the context of the underwater world, for the octopus. Underwater, water filters light, so things that are far away are gonna tend to appear dark. And so things in the environment like landmarks, finding their way back home or predators overhead, are all gonna appear as large dark objects and things that are close up are gonna appear light. So small things that for example, like food, that they might be grabbing.

So we think that their brain has maybe gotten optimized over the course of evolution to these aspects of the underwater world. And for me, that’s kind of exciting, seeing how a brain gets shaped to be able to match different types of environments and how different their underwater world is. And in particular, the things that are important to them.

The following transcript was created by a computer and edited by a volunteer:

Miller: Going back to just this question of the amount of real estate that visual processing takes up in our brains versus squid brains. What does it mean to say that 70%, sorry, not squid, those are the cephalopod cousins, octopuses. . .

Niell: It’s true in squids as well, actually.

Miller: OK, good. But what does it mean to say that 70% of their brains are involved in processing visual information?

Niell: So it’s true, just in the physical basis, if you look at their brain, there’s these two really large lobes. If you were to look at their brain, you think, oh that’s really most of what you see there. Everything else is kind of buried underneath those. These structures are called the optic lobes. They get the input from the photoreceptors. So basically directly when light hits the eye, this one set of neurons sends their axons into the optic lobes, there’s a whole lot of processing that goes on in there, pretty much, presumably everything from detecting spots of light to recognizing food versus predators. And actually, for the octopus and other cephalopods, figuring out what’s out there in the environment so that you can choose the appropriate camouflage pattern.

Miller: Oh, that’s a key, that’s not just running away but looking like the rocks next to you, maybe, so you won’t get eaten?

Niell: Exactly. So something that our brain doesn’t do, we don’t have the ability to change our skin pattern. And so our visual system isn’t necessarily analyzing the scene in that way. And so that was another thing we’re interested in looking at going forward.

Miller: We analyze to figure out what we should put on in terms of clothes, but not our skin.

Niell: Exactly. Yeah, we aren’t controlling our muscles in order to change our skin pattern in that same way.

Miller: So you can actually see the connection between those muscle neurons tied to the visual information?

Niell: Yep. And that’s kind of our eventual goal. So this first experiment was really to try and get the broad layout of how is the visual system organized? Does it have these maps?

How does it treat light versus dark? But what we’d eventually like to move towards is figuring out how that information gets used for different things. So how does it recognize food and go towards it? How does it remember where its home is, so it can find its way back there? And as you mentioned, for me, one thing that’s really fascinating is camouflage. How do you look out at the scene and then send signals out to your skin that create that appropriate camouflage pattern, something that’s almost alien like.

Miller: Often, I ask questions to researchers who work in different animal models and you know, a version of what’s the application to humans or how do we think about this in terms of humans? But you started by saying that one of the things that was exciting about this research for you is that unlike mice, just how different the visual systems of octopuses are. What’s it like for you to study an animal that is, I don’t know, more alien?

Niell: Well, yeah, as you mentioned, for me, that’s fascinating. I often compare it to if somebody gave you an alien computer, some alien technology, and said, “Can you figure out how this works?” As a scientist, I’m just hooked on those types of problems. So I also think it kind of expands our view - I guess, maybe no pun intended there - our view of how animals can see the world. Not everybody sees the world the way that we do. Different animals are focused on different aspects of their visual scene that’s important to them or what life is like underwater. Octopuses can even see things that we can’t see. They’re able to detect the polarization angle of light, which is something that our eye simply can’t detect.

Miller: What does that mean? I mean, I know you can have polarizing lenses like on your glasses or sunglasses, I guess filter out jumbly light and have a picture look clearer. That’s the way I’ve experienced it, looking at a reflection, say from a car windshield. What does it mean for an octopus to see polarization?

Niell: Yeah. So light is a wave and it can wiggle in different directions. It also has different wavelengths. That’s what we see as color. Interestingly, octopuses and other cephalopods mostly don’t seem to actually see color, but they can detect that direction that the wave of light is wiggling in. And, as you mentioned, that’s what polarized filters do. They block out a part of that, certain angles of that wiggling, which allows us to see things more clearly. It, for example, blocks out reflections and so on. But it’s actually very useful in the underwater environment. So things like a jellyfish that are transparent, even though they let light go through, they change that polarization of the light. It’s almost acting as if they’re acting like a color filter, but in a completely different dimension of light. And so this is something that might allow octopuses and other cephalopods to be able to detect transparent objects, like food, underwater, in a way that we wouldn’t be able to see.

Miller: So it might be nearly invisible to us, a transparent jellyfish, but it would look like a tasty, very visible meal, potentially, to an octopus.

Niell: But it would pop out to the octopus in a way that we wouldn’t be able to see. And so that’s the type of thing to me that it’s just fascinating, something that our brains can’t do, we can’t see that, their brain does it. And we’re actually interested in, maybe since they can’t see color, they’re treating that polarization information in the brain, the same way that we treat color information in the brain.

Miller: What are you most excited to learn next about octopuses?

Niell: I think for us, one of the big things is this kind of connection from how they see the world, to how they use that information to do things that are important for their survival. Another thing that was a little bit of a serendipitous study, you mentioned the fact that we’re studying octopuses because they’re so different. You might say, well, maybe that’s not gonna tell us anything that’s useful for humans. In a previous study that we had done, we were looking at the different types of cells in the octopus brain. And we actually found that there were a whole bunch of essentially immature neurons, you kind of think of them as newborn neurons, coming into the visual system. And for us, that was really surprising. In humans, all of our neurons are basically born before we’re born and you’re stuck with that number or maybe they even decrease over the course of your life.

Octopus’s brains continue to grow throughout their lifetimes. They’re always adding in new neurons. It’s kind of like if you had a computer and you’re kind of continually adding new chips into it as it’s functioning. But you can imagine that that aspect of being able to bring new neurons into a brain, and have them get wired in, could actually be very useful from a therapeutic perspective. If somebody has a brain injury or stroke, if you could incorporate new neurons to come in and repair. At this point, that’s totally speculation yet it’s something that would be a dream outcome of this. But I think it’s an example of the type serendipitous discoveries that can occur when you’re studying something that’s just so completely different.

Miller: Cris Niell, thanks very much for joining us.

Niell: Thank you. This was fun.

Miller: Cris Niell is a professor of biology and a member of the Institute of Neuroscience at the University of Oregon.

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