That Neuroscience Guy - Left Brain/Right Brain

Episode Date: June 18, 2021

Have you ever had someone tell you they are more left- or right-brained? Its commonly thought that we can have a more active left or right side of our brain, which leads to us being more creative or analytical. In today's episode, I discuss the neuroscience of hemispheric specialization, and how it affects our behaviour. 

Hi, my name is Olof Krogolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. Are you a left brain thinker? Do you think of yourself as being more logical and analytical? left brain thinker? Do you think of yourself as being more logical and analytical? Or are you a right brain thinker and you're a bit more creative than the rest of us? On today's podcast, we're going to talk about the neuroscience of hemispheric specialization and whether or not someone can truly be a left brain or right brain thinker. As you're all aware, the brain has two hemispheres, a left hemisphere

and a right hemisphere that are split by the longitudinal fissure, the gap between the two hemispheres. Now the brain isn't split the whole way through, of course. It's connected near the midbrain by the corpus callosum. And the corpus callosum is a pathway, essentially allows neural communication from the left hemisphere to the right hemisphere, and it allows neural communication from the right hemisphere to back to the left hemisphere. When I was a kid growing up, my dad made me watch a movie. It was called Dr. Strangelove, and there was a very interesting example of this. So Dr. Strangelove has a separation between his two hemispheres. They don't communicate. And in one of the scenes in the movie, Dr. Strangelove has a separation between his two hemispheres. They don't communicate.

And in one of the scenes in the movie, Dr. Strangelove's right hand is trying to choke him, and his left hand is trying to stop the right hand from doing this. And this is what a lot of people think about in terms of this left brain, right brain thing. Well, that's not what we're really going to talk about today, when the two hemispheres are actually separated. That is a neural condition and can occur, but again, not the focus of today's show. Now, a lot of brain function is separated and there is left hemisphere, right hemisphere specialization. Let's take vision as a starting point. Visual information comes into our eyes and both the left and right visual field or the left and right half of where you're looking is represented in both eyes. But as visual information flows

through the brain to the back of the brain at the optic chiasma, what happens is all of the information representing the right visual field actually travels back to the left primary visual cortex, and all of the information representing the left visual field travels back to the right primary visual cortex. So while our eyes see both the left and right side of the world, our brain is specialized. The left side of the brain is processing information from right visual space, and the right side of the brain is processing information from left visual

space. Now it is brought together and unified as visual processing occurs, but at these early stages there is this separation, which is a form of hemispheric specialization. there is this separation, which is a form of hemispheric specialization. This is also true of the motor system. Right now, for instance, if you flex your right arm, the brain activity controlling your right arm is actually in the left primary motor cortex. And conversely, if you were going to flex your left arm, that's controlled from the right primary motor cortex. So the motor system also has hemispheric specialization. The right side of the brain in the right motor regions control the left side of the body, and the right side of the body is controlled by the left motor regions. This is also true of the sensory system.

this is also true of the sensory system. If you take sort of the opposite of the example I used, if you just tapped on your right arm, you've got a somatosensation, you can feel that, and where that information is processed is actually in the left primary sensory cortex. And conversely, if you were going to tap on your left arm, that information would travel to the right primary sensory cortex. And conversely, if you were going to tap on your left arm, that information would travel to the right primary sensory cortex. So just as with the motor system, the sensory system is specialized. The right primary sensory areas are responsible and listen to information from

the left side of the body, and the right primary sensory areas listen to information from the left side of the body, and the right primary sensory areas listen to information from the left side of the body. So in a sense, there already is hemispheric specialization. But that's not what we're really talking about. What I really want to get into is whether the left side does things better than the right side, and eventually to whether someone can be more left brain and someone can be more right brain. Well, there is hemispheric specialization.

If we think back to vision, visual processing related to object geometry, object direction, object distance, and even the mental rotation of shapes, when you take a shape and manipulate it in your head, that has a bias to right visual areas in the brain. So spatial ability has this sort of rightward bias. If we look at the processing of other visual information, for instance, when you read letters and words there is a left side

bias and we're going to come back to that in a second. And when you look at faces and facial expressions and geometric patterns there is a right visual bias again so there's more processing on the right side. In terms of the motor system this is also true. Complex movements tend to evoke more activity in left motor regions and movements that are tied to spatial patterns. So if you're following a specific pattern with your body are tied more to the right motor system. Now getting back to speech, and this is also a part of the motor system, The primary area for speech comprehension is called Wernicke's area,

and that is in the left hemisphere. It's in the left posterior regions of the brain in the superior temporal cortex. And speech production is also tied to motor areas on the left hemisphere, specifically Broca's area, an area that's important for speech production. So the understanding of speech, at least at a semantic level in the production of speech in terms of making the actual sounds, do have this left hemisphere bias. So with that being said, with creative speech like poetry or music, singing, for instance, you typically see more activation in the right corresponding hemispheres. So language does have this hemispheric bias.

The understanding and comprehension in terms of semantics and the production of spoken language is tied more to the left side than the right. And production of creative speech, poetry and singing is tied more to the right. than the right, and production of creative speech, poetry and singing, is tied more to the right. Now I want to be clear here, it's not like it's only on the left side or only on the right. Typically you see bilateral activation, but there's just more of a bias. There's more processing on the left side or more processing on the right side. on the left side, or more processing on the right side. There's other things that have hemispheric bias.

For instance, math. The left angular gyrus, which is in the left posterior regions of the brain, is tied to mathematical understanding and processing and computation. So math, or at least doing the computations and understanding numbers, appears to have this leftward bias. However, if you were reading more into geometry and spatial representations, then there'd be more rightward processing. Now, so far I've talked about, you know,

vision in the motor system and the sensory system, but what about higher level cognitive constructs like attention? Well, attention is an interesting one. It appears that the right attentional system is more concerned with general attention, so being aware of all of the world that is around you, and the left attentional system is more concerned with generating specific attention to an area or a spotlight of attention, if you will. So our attentional system has this left and right hemisphere bias. This hemispheric bias is also true of memory. When we talk about working memory, so the memory that we use when we're just learning something or we recall something from long-term memory,

verbal working memory has a left hemisphere bias and is associated specifically with the left ventrolateral prefrontal cortex. And spatial working memory, when we're trying to remember an image or we're recalling an image, has a right hemisphere bias. We see more activity in the right ventrolateral prefrontal cortex. So as with attention, our memory system has this hemispheric bias. Now, if we take this to a higher level again, we can talk about decision making. For this, I'll talk about a specific research study from my own lab. A couple of years ago, me and a colleague of mine decided to put medical students and expert clinicians into an fMRI scanner to look at their brain activity.

And the brain activity that we were looking at is what was going on when these medical students and the expert clinicians were diagnosing clinical cases. So the students and the doctors went into the fMRI scanner, and we literally showed them a clinical case. They got the symptoms of the patient, and they got some diagnostic measurements, and they had to diagnose the case while we were recording their brain activity. We did this, like I said, in a bunch of medical students and a bunch of doctors. And when we looked at the data, we saw something really interesting. We found that the medical students had a left brain bias

and the experienced medical doctors had a right brain bias. Now, all of the activity was in the prefrontal cortex, a region that is associated with decision-making, but we weren't expecting this left versus right bias. And when we dug into it, we realized it made sense. The leftward bias was associated with the medical students relying on semantic knowledge, what they read in books and what they'd learned in classes. And the right bias that we saw in the expert clinicians was them relying on experience, not thinking back to what they learned in a textbook, but thinking back to what they had actually seen and experienced in

their own medical career. So decision-making also has this left or right side bias. The left side is tied more to relying on your book base or factual knowledge, and the right side seems to be more biased towards the processing and use of experience in decision making. At a higher level, it's been put forward that the left hemisphere and the brain systems there basically are responsible for coming up with our belief system of the world. So how the world around us actually works. We call this model formation. The left hemisphere builds a model of the world. So I believe that this is the way gravity works, for instance. And the right hemisphere and the prefrontal regions are more concerned with questioning the model and revising the model. So you develop a model for the way you think the world works. And the left hemisphere is responsible for building and maintaining that model.

And the right hemisphere is responsible for questioning that model and even prompting change when it's necessary. Now, I've talked a lot about hemispheric specialization. We've seen that at a sensory level, at a motor level, there's processing on the opposite side of the brain. So if you remember, left visual information is processed on the right and right visual information is processed on the left. And then we went a little bit further. We talked about some brain regions that are specialized.

The fact that the left side of the brain is more specialized for semantic knowledge and the right side of the brain is more specialized for the creative aspects of language. But can you actually be a more left-brain person or a right-brain person? Well, it turns out it's a myth. The reality is that these brain regions can be influenced by practice. So for instance, if you spent all of your life writing poetry or writing music, the right brain region would probably be a little bit more developed than that of the average person. But you're not born that way and it doesn't make you a right brain thinker. My name's Olof Kregolsen and I'm That Neuroscience Guy. You can follow me on Twitter, that neuroscience guy. You can check out my YouTube channel, that neuroscience guy, or you can check out my website, www.olivkregolson.com.

And if you've got questions that I might address on a future episode or an idea for a show, please email me at that neuroscience guy at gmail.com. Thanks for listening.