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Our two-sided and half billion-year-old brains

In today’s blog we explore the evolution of the brain with Dr. Gillian Forrester, PhD from the University of Oxford, Reader in Evolutionary and Developmental Psychology, and the Deputy Dean for the School of Science at Birkbeck, University of London.


David: Our brains have two sides. How common is that? Do we have a sense of how brains have evolved? Can we extrapolate from the pressures of the environment to the way brains evolved on Earth to get a sense of what brains could be like elsewhere in the universe?


Gillian: All the big questions, huh? Vertebrate brains emerged 500 million years ago during the Cambrian period. Population trends across species suggests that there is this hemispheric divide and that seems to be a healthy and normal type of brain. They all have the old vertebrate brain components, the forebrain, the midbrain, the hindbrain, that all do their specific roles in sensory integration, in behavior and planning, and so forth. But those bits have been twisted and turned, pushed and pulled, due to the pressures in the environments that those different species evolved in. So, you can see how they took different shapes and have increased or decreased their roles in these different species. Nevertheless, there seems to be the two hemispheres that have specific kinds of dominances that control different kinds of behaviors on the opposite side of the individual’s body. So, we do know that.


David: Are these two sides of the brain there because we need to do different things at the same time?


Gillian: This is theory that is being borne out in experiments to see whether, or not, it’s consistent with theory. Going back to the 1860’s, 1870’s, we already knew that the human brain had these two sides that have slightly different dominances because of Paul Broca and Carl Wernicke’s work in language and aphasias with individuals who had damage to one side and had particular loss of cognitive ability. We thought that was interesting and special to humans because we associated it with our language abilities and language was human unique. So, we just assumed that what we call cerebral lateralization, which is this dominance to a particular side, was also human unique. But more recently we’ve had lots of studies across many different animal species that are returning very similar patterns across the board, where the left hemisphere is dominant for particular motor action sequencing types of behaviors. And these are behaviors that underpin a whole host of different kinds of animal behaviors, that range anywhere from which foot do you put forward first, to what do you grasp with, to using tools, to using language. All tend to be underpinned by motor action sequences that require some sort of hierarchical processing. And then we’ve got the right hemisphere that seems to be more involved with fight-or-flight, keeping you safe from unexpected or threatening stimuli in the environment. Again, it’s involved in a whole host of things that on the surface might look very different but probably powered by some rudimentary need for survival. And so, the hypothesis is that if you have two sides of the brain, well why don’t you just replicate everything onto both sides, as that gives you lots of backup? Well, then both sides would be competing for response, and you get incompatible responses that muddles the individual and we can see that happen in split-brain patients. If we make slight dominances, with lots of replication, then you will have one side taking charge, which does mean that you can do two things at once more systematically. The original studies were classic studies with chicks because each eye is directly controlled by the opposite hemisphere. So, such studies by Giorgio Vallortigara and Leslie Rogers, I think in the 1980’s, did a lovely set of sequential studies that looked at chicks who had hatched normally with normal incubation period, and normal exposure to light. When these chicks hatched, they gave them little tasks to see what their dominances were like. And one of the tasks was they sprinkled pebbles and grain on the ground and they watched them peck for the grain to see if they could discriminate well between the pebbles and the grain, which they obviously could do quite well, and whether they had a visual preference. Did they have an eye preference for locating the seeds in which case they’d expect the chick to put that eye towards the ground a bit more. And they found that testing many chicks over many trials, that the species indeed has a right eye bias and therefore the left hemisphere seems to be controlling this more dominantly than the right. And it doesn’t mean you don’t get chicks that go the other way, that you get some bilateral individuals. The overriding population trend shows this right eye bias. And then likewise they flew a fake, cardboard cut-out hawk, over lots and lots of chicks for lots and lots of trials to see if they had preference for which eye they would look out for danger. And low and behold, they found a left eye bias for looking up to the sky for dangerous predators. Now if we put the two tasks together this makes like an eat-and-not-be-eaten parallel processor, one eye to the ground so the organism can feed itself, one eye to the sky to watch for predators, two basic survival capabilities in tandem. And they looked at lots of other animal species and found that where you had a good division of labor between the two hemispheres, the survival rate of the organism is better. So, it seems to be good for survival fitness. And they also took a bunch of chicks and messed with their exposure to light so that the two sides of the brain didn’t have the same dominances. They disrupted the dominances of the two sides for visual processing and found that these chicks could do both tasks just fine but they didn’t have a bias. So, when you put the two tasks together, they were more vulnerable, and they would have been eaten by predators. So that’s kind of where the theory stems from about why we have the two sides.


David: Why not three eyes and three parts to the brain? Or maybe the survival ability would decrease if you divide things up further? Maybe two sides maximizes the abilities?


Gillian: Yeah. It seems we have these different kinds of variables with brains. They’re all kind of made up of the same stuff but they grow at different rates, and different portions of them grow at different rates. And it does seem to be a lot down to the more of the stuff you have, the better resources you have. That’s true very roughly when we say that big brains are good. But it doesn’t hold true when you look at birds. Elephants have massive brains. Dolphins have big brains for the size of their bodies. Dolphins have an extra whole lobe compared to humans. So, there are a lot of exceptions to the rule, and I think what we’re finding is that for humans it is more about our association cortices. So, the frontal lobe that ties together sensory perception, experiences of the world and planning, they seem to be things that are quite important to our communication systems which seem to be responsible for so much of our cultural abilities and capabilities. And birds likewise, even though they have very small brains, they have a large association area, and they also seem to be very adept communicators, with sophisticated communication systems. So, I don’t think we know enough to make any hard-and-fast conclusions about it.


David: In my research, we are trying to understand very counterintuitive things about space, time, and matter. Given that our brains have evolved to make sense of a very specific environment, I wonder if we should expect our project of exploring physics more deeply to stall.


Gillian: Yeah, completely. My daughter did a dissertation thing on one of her projects on whether we are just limited by the cognitive tools we have. So, language is usually limiting in many respects. If you don’t have the word for something, do you therefore not have the concept? Yeah, I think that’s hugely fascinating. I think we miss out on a huge amount of information around us because we don’t know how to perceive it or conceive of it. But likewise, we also don’t understand how other animals function or even ourselves for that matter because we don’t necessarily have the tools or the perspective. I think we’ve spent so many years looking at other apes and thinking “Ah, they should talk like us”. Let’s teach them to talk because surely that’s the way we can communicate with them. Versus, let’s try to learn how they communicate and maybe we will gain some insight into the way they think and the way they emote and the way their social dynamics works. Maybe we can tune into and not assume it’s going to be just like ours or it’s going to be a poorer version of ours. Let’s look at it from an aliens’ perspective that we don’t really know how this thing works. Can we find patterns in the data that will illuminate a new system that we didn’t even know was sitting right there under our noses? I think that’s the case with dolphin and whale communication which is so different from our own. Octopuses – oh my gosh – I think they have incredible communication systems that we know nothing about. And so it doesn’t have to go even beyond Earth. I think a lot of it is here and we just don’t get it yet because we just haven’t been able to look outside our very boxed-in perspective.


David: Is there anything you think should be more widely known?


Gillian: I want people to understand that humans are not totally unique in our capabilities. That we only have the capabilities we have through an evolutionary process. And that even though we have cognitive abilities that look very sophisticated on the surface, they’re gonna be powered by things that were more basic originally and we’ve expanded upon them. Like our language system. It didn’t come out of nowhere. It wasn’t a spontaneous eruption, but it would have emerged from precursor capabilities, probably ones that we share with the last common ancestor. Our gorilla and chimpanzee cousins will have inherited them as well. If we can focus more on our connection to other animals with whom we share an evolutionary history, we’ll learn far more about ourselves. Particularly, I am interested in how motor processing like tool use and tool manufacturing, the way we solve problems with our hands and move objects around, was useful and set our brains up for language.


David: Could we imagine engineering language into apes over faster timescales?


Gillian: Sign language worked much better with apes. Lexigrams work much better with apes. They have much larger vocabularies. It’s the syntax that is still different from ours. For me, the direction is that if we understand that our higher cognitive functions emerged from more simplistic motor action sequencing, then what can we take from that and learn from when human infants develop. Now, they don’t have language when they’re born. So, what is it sitting on? What needs to develop before, to allow it to emerge during development, and can we learn anything from our evolutionary trajectory that will help us understand that developmental process better? And, also, when it deviates from typicality. Currently, we only know at about age 3 or 4 that the child is autistic because they haven’t started producing the typical social and language behaviors that you would expect of a child of that age. But, if it stems from something that’s gone differently or disrupted in the motor processing system, we should be able to see that very early on, during infancy, and have an idea if there are particular individuals at risk for developing these sorts of disorders. I think we are in an early place in the field.


David: Does part of your work involve creating experiments?


Gillian: Yeah. We just finished a short video with New Scientist on the study that I’m currently doing, which, exactly as you suggested we’ve got to create new studies that can cross species and not give humans the benefit because they understand language. How can you create studies that will allow you to take the language load out as a confound and still learn something about it. Let me send you a link about this (see below). Well, good luck with the blog.


David: I’ll put it together and send you the transcript and you can change what you don’t like.


Gillian: Awesome.


David: Thank you professor!



The language puzzle: What great apes can teach us about the evolution of speech

https://www.youtube.com/watch?v=8edayRfe484


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