That Neuroscience Guy - The Neuroscience of Attention-Deficit/Hyperactivity Disorder (ADHD)

Episode Date: November 28, 2022

ADHD is a prevalent neurodevelopment disorder that typically involves enhanced impulsivity, trouble with paying attention, and/or general hyperactivity. In today's episode of That Neuroscience Guy, we discuss the neuroscience behind what causes ADHD, and how it affects the brain. 

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. Attention Deficit Hyperactivity Disorder, or ADHD, is one of the most common, if not the most common, neurodevelopmental disorders that can occur in children, and it can continue through into adulthood. So finally, by popular request from the listeners, on today's podcast, the neuroscience of ADHD. The most common symptoms of ADHD are having trouble paying attention, so not being able to focus on specific things, having trouble controlling behavior, so doing things that may seem appropriate

given the situation, and being restlessly or overly active, not being able to sit still or wanting to move. However, there are a lot of other symptoms that are typically seen, and they include daydreaming a lot. People with ADHD can be lost in thought, like they're focused on something else. They can forget or lose things a lot, specifically things that you think they would remember, like keys or things like this. But it depends a lot on the person. Squirming or fidgeting is really common. Talking too much or talking at the wrong time. Making careless mistakes or taking unnecessary risks.

Having a hard time resisting temptations. Having trouble just changing direction, whether it's in life or just moving. And having trouble getting along with others. Now, someone with ADHD might not have all of those symptoms. They might have one or two. That's what's interesting about ADHD. Well, to be fair, there's a lot of interesting things about ADHD is that not everyone presents with the same symptoms. So if you heard that list and you have ADHD, you probably checked off one or two things, but probably not all of them. And of course, age factors into this as well. Now, there are typically considered to be three types of ADHD. There's predominantly

inattentive presentation. And with predominantly inattentive presentation, it's hard for the individual to organize or finish a task, to pay attention to details or follow instructions or conversations. The person is easily distracted and sort of forgets their daily routines. Then there's predominantly hyperactive impulse presentation. This is the person with ADHD that fidgets and talks a lot. They don't sit still well. They won't sit through a meal or while doing homework. They're going to get up and move around.

Smaller children, they'll just be moving constantly, whether it's running or jumping or climbing. And the individual generally feels really restless and they have trouble with impulsivity. They just want to do things. So someone who's impulsive, they might interrupt you. They might take something from you. They might grab. They're just doing things at the wrong time that don't make sense. And then there's combined presentation. There's symptoms of the two other types, and they're both there. So with combined presentation, you would have both symptoms of predominantly inattentive presentation and also predominantly hyperactive impulse presentation. Now, what causes ADHD? Like,

why does someone have ADHD? And the biggest belief to date is that it's genetic. You come hardwired for ADHD in a sense. Now, we've talked about genetic causes before on the podcast, but we haven't really dove really into what that really means. So I'm going to take a little dive here. Well, DNA, as you probably know, is crucial to our existence. It's basically the building block of life. Deoxyribonucleic acid, that's what DNA stands for. It's a molecule and it carries genetic information for the development and function of the organism. So you. And basically, the way it looks is really cool. If you get a chance, Google image DNA.

And I might even do the bite on DNA just to show you it. But basically, it's like two link strands and they wind around each other. And it's like two ladders that get twisted together. It's kind of what it looks like. Now, scientifically, you would call this a double helix. Now, the way it really sort of fits together is each strand has like a backbone or a framework that is made of alternating sugars and phosphate groups. But the most important part are the bases attached to the sugars. These are like the little rungs of the ladder that go across. And these are adenine, cytosine, guanine, and thymine. And these bases are crucial. The reason being is it's the sequence of the bases along the DNA

ladder, if you will, that encode information. So it's the actual order these things are in. And these might be instructions for something as simple as making a protein or an RNA molecule or things that add up to the way you behave. Here's a cool fact actually about DNA. For any two people, if you take any two people, 99.9% of the DNA is identical. That's true. That's been scientifically determined. It's just that 0.1% difference that encodes all of the differences we see between ourselves. That differing 0.1% contains variations that influence our uniqueness, like the way we behave, the way we look, our health, our behavior. And in this case, some of those differences can lead to ADHD. Now, all living

things have DNA within their cells. In fact, nearly every cell in your body possesses the full set of DNA required to make you. This is how cloning works in a sense. If you can get that information, you can make a person from it. It's important though to realize that it's not just structure. It basically helps with reproduction in a sense. And what I mean by that is when organisms reproduce, a portion of their DNA is passed along to their offspring. And it's the combination of that DNA that leads to changes. So it plays a key role in how we're evolving as well. And it's all these slight little changes and these slight little differences

that lead to the diversity that we see. All right, so that's a lot about DNA, but what's a genetic disorder if you think of ADHD as a genetic disorder? Well, a genetic disorder is basically, medically you would call it a disease, but it's when the whole or part of the DNA sequence is changed. It's not normal. Now, it can be caused by a mutation in one gene, which is called a monogenetic disorder, or mutations in multiple genes, which go under the name of a multifactorial inheritance disorder. And these differences can be by a combination of gene mutations and environmental factors, or by damages to chromosomes. So the DNA itself, and is it within your cells, and the

genetic disorders are when there's changes within these cells. So with ADHD, it's believed that within the DNA sequence, there are tiny differences that lead to the differences in behavior we see in people with ADHD. Now, in addition to this genetic cause, which is the primary cause, scientists are looking at other factors. For instance, people with brain injury sometimes present with ADHD-like symptoms. Exposure to environmental risk can cause ADHD. So, for instance, fetal alcohol syndrome can lead to behaviors that are akin to ADHD. And this ties into alcohol use during pregnancy and tobacco use as well,

which has also been implicated. Premature delivery, babies that are born too young, sometimes, not every time, can present with ADHD-like symptoms as they grow up. And low birth weight is tied to this as well, but those two are yoked. Now, it's important to know that research doesn't support a lot of the nonsenses out there. And when I say nonsense, I want you to refer to the previous podcast about interpreting scientific data. There is no scientific evidence to support that ADHD is caused by eating too much sugar, watching too much television, parenting, or social and environmental factors such as poverty or family disruption. Now these things might make symptoms worse, of course, but it's primarily a genetic disorder, which means it's not impacted at that level by these things, at least not to the best of our understanding right now. So with ADHD, let's get to the neuroscience of it. What's going on in the

brain? Well, at the heart of it, ADHD and those genetic differences we discussed results in differences in levels of neurotransmitters and two neurotransmitters in particular, norepinephrine and dopamine. Now, if you remember really quickly, we've talked about this a lot, but in case this is the first time you're listening, the way the brain works is pretty straightforward. A neuron fires, it's an electrical signal that's sent down the axon of the neuron. When it gets to the end of the axon, it releases neurotransmitter. It's the chemical that causes synaptic transmission. And that neurotransmitter binds at a postsynaptic neuron and it generates an electrical signal. So the whole purpose of neurotransmitters, literally in the name, it's to promote and

facilitate neural communication. Why are there different neurotransmitters? Well, they occur in different parts of the brain and have different purposes. So dopamine, for instance, plays a role in reward, whereas norepinephrine is tied to decision-making and the neurons that underlie these processes. Now, the result of this reduction in norepinephrine and dopamine results in functional differences in various parts of the brain. So, for instance, the reduction in norepinephrine in the prefrontal cortex and also a bit of a reduction in dopamine results in changes in attention. And that's where the attentional deficits come from. Changes in executive

function. So the impulsivity or the ability to not stay on task and changes in just organization, how we plan. And those changes that we see in the real world are due to differences in the prefrontal cortex, which are driven by those differences in neurotransmitter levels. Now, it's not just the prefrontal cortex that hit, it's also the limbic system. Now, if you remember, the limbic system is a midbrain region. I'm not particularly a fan of that term, but it is widely used. But at the end of the day, it's your emotional system, and it also plays a bit of a role in attention. And again, it's those reductions in norepinephrine and dopamine that result in differences in the function of the limbic system,

which results in the behavioral differences we see in ADHD. This is also true in the basal ganglia. If you remember, the basal ganglia is a collection of midbrain nuclei. They play a role in motor control, learning in a bunch of processes. And yet again, the reduced levels of norepinephrine and dopamine in people with ADHD result in differences in these processes. And finally, differences in the reticular activating system. This is basically, it's a major relay system. And I'll talk a bit about it in the future episode, because I realize I haven't really talked about it.

But at the end of the day, the differences in neurotransmitter in the reticular activating system result in the inattentive behavior, the impulsivity, and the hyperactivity that we see in people with ADHD. And you can see these differences in terms of research. When I was a PhD student, a master's student in the lab was measuring learning signals in the brain in kids with ADHD and without ADHD. It was a pretty straightforward study. Kid would come in that have a medical diagnosis, ADHD, not ADHD. And we made them learn something. They went through a simple learning task and we measured their brainwaves. And lo and behold, the people with ADHD had a reduced reward response to feedback in the learning task.

And why is that? Because that reward response that we were studying is driven by dopamine. So the reduced levels of dopamine in the people in the study resulted in a reduced neural signal, which was implicated in why they might have trouble learning. Now, what do you do if you have ADHD? Well, the reality is that ADHD is best treated by a professional clinical neuropsychologist or medical doctor, and they're going to use a combination of behavioral therapy and medication. The exact way they apply that is really a medical decision. It depends on the case in question. But as ever, healthy brain habits can help with ADHD. So people with ADHD, their symptoms are reduced

if they eat a healthy diet. So what we've talked about when we talked about good brain health and diet, plenty of fruits and vegetables, whole grains, and choosing lean protein sources. Daily physical activity has been shown to help reduce ADHD symptoms. So just getting out and being active. An important one that we haven't talked about as much, but is completely true, is limiting the amount of daily screen time. So whether it's TVs, computers, phones, and other electronics, those things are thought to amplify ADHD-like symptoms. So reducing that use of electronics can help with ADHD-like symptoms. And then finally, of course, we've talked about it a lot,

but one of the best things you can do for brain health is also something can help with ADHD symptoms, and that's getting the right amount of sleep each night. Remember, seven to nine hours is the goal, consistentistent seven days a week. All right. Well, there it is. As requested by you, the listeners, the neuroscience of ADHD. Please remember, you can follow me on Twitter at thatneuroscienceguy and just DM me personally. I'll respond. Send us some ideas. A couple more episodes coming up are all driven by user input. And of course, there's our website, thatneuroscienceguy.com. Remember, there's links to Patreon.

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back to you on Wednesday with another neuroscience bite. My name is Olive Craig Olson, and I'm that neuroscience guy. Thank you so much for listening and I'll see you on Wednesday.