That Neuroscience Guy - The Neuroscience of Autism

Episode Date: October 9, 2022

Around 75,000,000 people, or roughly 1% of the world's population, have autism. Autism is a broad term for individuals with a variety of atypical behaviours, such as social interaction and communication. But where might those differences come from? In today's episode of That Neuroscience Guy, we discuss the neuroscience behind Autism. 

Hi, my name is Olof Kregolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. A lot of people have heard of autism. Indeed, there is a large number of people who believe they are autistic or are actually on the autism spectrum. But what is autism actually and what do we mean when we say people are on the spectrum? Indeed, the concept of neurodiversity is important to understand. We are not all the same. Just as we

have differences in height and weight and appearance, our brains are all different as well. So the way that we move, the way that we think, and the way that we behave is different. Our brains are as unique as our outside of our body. So with this in mind, on today's podcast, the neuroscience of autism. Now, before I get going, I'm going to talk a little bit about labeling. I'm going to use the phrase autism throughout the podcast, but you may have heard of autism spectrum disorder or autism spectrum condition, ASD or ASC. They all mean the same thing, and I believe the word autism is preferred because the idea of saying it's a disorder or a condition isn't exactly a correct label.

So autism is a developmental disability caused by differences in the brain. Interestingly, some people with autism have a known difference, such as one caused by a genetic disorder, while in other instances, the underlying cause is unknown. In other words, there are multiple potential causes for autism that lead to similar signs and symptoms. In general, people with autism may behave, communicate, interact, and learn in ways that are different from other people. But the degree of that difference can be very minor to the

point that it is not noticeable or to the other extreme where it is. And that's why I said the word may. Some people with autism have no outward signs or symptoms, or even within their degree of autism is very minor, whereas other people are quite extremely impacted by autism. For example, some people with autism communicate at an above-average level or greater, whereas others can be non-verbal. So the differences with autism can be quite mild or quite extreme. Now typically autism begins before age 3 and generally lasts the lifespan, although with work and support in some instances the symptoms will improve over time. support in some instances, the symptoms will improve over time. Some children present with autism shortly after birth, whereas other children don't show any signs or symptoms until 24 months or even later. And even further, in some instances, children with autism progress normally until a

point, and then they begin to backtrack and lose abilities and fall behind typical development. begin to backtrack and lose abilities and fall behind typical development. In general, how autism occurs is not well understood, and research is ongoing. But with that said, there are some scientific theories. Perhaps the most prominent theory currently relates to synaptic dysfunction. And we all remember synapses from recent episodes. That's the junction between an axon and a dendrite where neural communication occurs. So one theory is that the neural synapses of people with autism are not functioning the same as the synapses of people without autism, perhaps due to mutations that are genetically driven or due to another outlying cause. Other theories of autism focus

on what is called the gut-brain axis, with the basic idea being that problems with the metabolic system lead to brain inflammation, and that leads to brain dysfunction. This theory is supported by the increased incidence in things such as reflux, constipation, inflammatory bowel disease, and allergies that are seen in people with autism. And there are many, many other theories out there. It's just something that's in progress. Just as there are a range of potential causes for autism, there are also a range of differences in the brain that are observed. Within the brain, autism is associated with deficits in the production of complex behaviors, language and cognition.

But what causes these differences? It was originally thought that people with autism typically have a slightly larger brain volume than those without autism. However, more recently it's become clear that that's not true. The discrepancies in brain volume are not universally on the large end.

Some regions are larger, but some regions are smaller. What causes this? Studies suggest that autism may be caused, and this difference in brain size specifically may be caused, by abnormal neuronal growth and pruning during the early stages of prenatal and postnatal brain development, leaving some areas of the brain literally with too many neurons and other areas with too few neurons. We'll touch on this a bit more in a few minutes. But before we go further into this, a definition. What is meant by neural connectivity? Well, quite literally it means the connectivity of neurons within the brain. And there is an optimal amount of connectivity for normal neuro-processing. If a region of the brain is over-connected, it can lead to problems.

And if a region of the brain is under-connected, it can lead to problems. Just think of a highway as an example of this. A highway is a form of connectivity between two points, city A and city B. And if the road is too narrow, you're going to have a traffic block up. All right. There's too much traffic and things can't progress the way they're supposed to on the road. But if the road's too big, it's kind of a waste. All right. And you're wasting resources because you might not need an eight lane highway. So neural connectivity is the same. You want a brain region to be connected to another brain region with just

the right amount of connectivity. Basically, with people with autism, there's a decrease in brain connectivity between brain regions, so over vast distances across the brain or between separate brain regions. And within brain regions, there is over-connectivity. So what does this actually mean? Well, between-region connectivity is typically associated with the overall processing and understanding of information, in addition to integrating new sensory information within the current model of what's going on. Whereas conversely, within-region over-connectivity is associated with attention to detail. The brain region becomes too focused on one thing and sort of misses the big picture. So, for example, decreased brain connectivity between regions

would be like missing out on some kind of new sensory information about an object. Or even the fact that the object is there. Whereas within region, over-connectivity would be like focusing in on details and some specific detail of the object once it's detected. This example is paralleled by left and right brain differences that are observed in people with autism. People with autism typically have a bias towards left brain processing, which aligns with paying attention to detail bias towards left brain processing, which aligns with paying attention to detail, whereas right brain processing is more typically associated with

global processing of information. A classic example of this would be looking at a car. The right brain plays more of a role in figuring out that it is a car, and the left brain might be more focused on the detail of the tires. So someone with autism is sort of having trouble with the bigger picture in global processing and they're really focused in on the detail due to this preferential processing of the left brain relative to the right brain. In more extreme instances of autism, it is typical to see greater connectivity within the left hemisphere and reduced connectivity in the prefrontal cortex. Now, differences in autism are also seen in the limbic system. Back to the amygdala again, my apologies. But this is directly tied to emotional processing differences, which in turn may contribute to the social impairments that

can be seen or may be seen in people with autism. To expand on that a bit, people with autism can or may have trouble with social engagement, interacting with others relative to someone with more typical development. There's also differences within the cerebellum, and these differences can be seen in the number of Purkinje cells, it's a type of cell that was within the cerebellum that plays a role in various neural processes, and this can lead to problems with motor output and potentially with speech production. There's also reduced function seen in the temporal lobe, and that's related to other deficits that can be seen in people with autism, and that's related to other deficits that can be seen in people with autism,

such as reception of language, social cognition, attention as a group, observing the actions of others, and empathy. And these deficits in the temporal lobe, again, are related to reduced neural function. Even neurotransmitters are impacted, serotonin in particular. Serotonin does a lot of things, but in particular plays a role in the formation and pruning of neural connections, which may be a reason why people with autism can have trouble with learning. Interestingly, even the mirror neuron system is implicated. So the mirror neuron system is a group of neurons within the brain that are active when we observe other people, and they basically act to mirror, hence the name, what's going on with another person within the brain. And this could be why some people with autism have a lack of empathy, because they can't see the other person, or at least their mirror neurons can't detect the other person, therefore they have trouble processing what the other person is doing other person therefore they have trouble processing what

the other person is doing and therefore they have a lack of empathy this even relates to something bigger which we're going to talk about in the future called theory of mind but theory and mind in brief is our ability to understand that we are a conscious being and that the people around us are conscious beings and that we are able to process our own information about the state of ourselves and process other people more importantly. And people with autism typically have a reduced ability with theory of mind, which means they have trouble understanding the emotions and the feelings of other people. And again, that's a may. Not all people with autism have that. So that's a great note to end on. When we say that autism is a spectrum, it's important to realize it's not linear.

It's more like a tree with many branches. Some people have autistic symptoms and behaviors that are on one of those branches, and the same people might have none on the other branches. So it's not like this line that you fall somewhere on it, where it might be not at all or completely. It's a tree where everyone probably has a little bit on some or more of these branches. And if you think of that, empathy is a good example. Whereas some people might have some issues with empathy, which would be seen as a mild form of autism. So to sum up overall, the underlying causes of autism are not clear. A whole bunch of brain regions are impacted, typically with differences in processing. So some

brain regions are over-connected, some are under-connected, and sometimes there's a left brain bias versus a right brain bias. So that's a lot on autism. Hopefully you enjoyed the podcast. As ever, you can check out our website, thatneuroscienceguy.com. That's got links to Patreon where you can support us. Remember all of the money goes to graduate students in the Craig Olson Lab. You can also buy t-shirts from our Etsy store. We're working on a few new designs. And if you've got show ideas, we're still trying to flesh out the end of season four. So you can follow me on Twitter at thatneuros neuroscience guy and dm me or you can send us an email at that neuroscience guy at gmail.com my name is olaf kirk olson and i'm that neuroscience guy thank you so

much for listening to the podcast and i'll see you on wednesday for another neuroscience bite