Identifying Brain Differences In People With ADHD

Researchers examined the brains of people with attention deficit hyperactivity disorder (ADHD) and found differences that make them less sensitive to rewards. Nora Volkow, director of the National Institute on Drug Abuse, discusses what the findings may mean for treatment.

IRA FLATOW, host:

This is SCIENCE FRIDAY from NPR News. I'm Ira Flatow.

Attention Deficit Hyperactivity Disorder, ADHD, is sometimes described as paradoxical. On the one hand, you give people with ADHD something that they really want to zoom in on and they have no trouble focusing, like they might have. Let's say, if they were in a classroom or if they were just trying to do something else. It's paradoxical here. On one hand, they can't focus. Let's say, they're jumping around in the classroom like kids might do. On the other hand, you give them something they really like to do and they can hyper focus and zoom in on it.

Why is that? That is something that has always really been a problem in understanding. And now, a new study in the Journal of the American Medical Association, there might be an explanation because researchers looking at the brains of people with ADHD have found key differences in the reward pathways of the brain.

What does reward have to do with attention? Nora Volkow is the director of the National Institute on Drug Abuse at the National Institutes of Health and the lead author on the new study. And she's back to talk about it with us. Hi. Welcome back to the program, Dr. Volkow.

Dr. NORA VOLKOW (Director, National Institute on Drug Abuse): Good afternoon. How are you?

FLATOW: How - you have found that there are different rewards or reward pathways in the brain for people with ADHD and people without it.

Dr. VOLKOW: No. The reward pathway is the same. What we were actually investigating was whether there were changes in the function of the dopamine reward pathway in the brain in individuals who suffer from attention deficit hyper activity disorder.

So, they still use imaging specifically to monitor different markers of the dopamine system in the brain of individuals with ADHD. We studied 55 of those individuals and 43 healthy controls and then compare the brain of these two groups of subjects. And found that indeed as what have been suggested by clinical stories. There was a significant deficit in the function of the dopamine reward pathways in individuals that have ADHD.

FLATOW: So, you felt more reward if you got - if you're focused.

Dr. VOLKOW: Well, it's - what we are finding is there is decreased activity of the reward system in individuals with ADHD with which translate into a decreased sensitivity to being able to be engaged…

FLATOW: Right.

Dr. VOLKOW: …by stimuli that are not inherently rewarding or reinforcing. And this could explain what you were introducing the paradoxical perspective of many parents that say, well, you know, my kid can spend hours playing video, focused and attentive. And yet they cannot focus at all at school.

Well, the difference is that the video is inherently rewarding and reinforcing. And by being inherently rewarding, it activates the dopamine system. And the activation of the dopamine system is indispensable to motivate you and engage the attentional network. By having a deficit in the function of the system, it requires a much stronger stimuli to engage an individual with ADHD such that that person gets motivated on - interested on the task, which will then allow him to engage (unintelligible) attentional networks of the brain.

FLATOW: So there - it looks like you have two options then. Either to find -let's say for kids, to find teachers who are really good at motivating, you know, to pay attention or giving you a great reward when you do that or to find maybe some drug pathway, right, that might be able to do the same thing.

Dr. VOLKOW: Well, my perspective is that you actually aim for both. Try to provide alternative interventions. But definitively that challenge of creating an educational curriculum that is more engaging will definitively improve the performance in individuals that have ADHD.

Indeed, it improves the performance of anyone. If you're performing a task that is boring and repetitive, your performance will go down and the issue is that threshold at which your performance starts to go down vis-a-vis the tasks that you're performing, and in ADHD that threshold is much lower. And those - you require a greater…

FLATOW: Yeah.

Dr. VOLKOW: …effort to make the stimuli challenging and interesting.

FLATOW: So, this study explains, then, why ADHD medicines work because they've raised the baseline level of the dopamine.

Dr. VOLKOW: Well, it provides an explanation and indeed we have previously shown that the medications used for ADHD, stimulant medications like amphetamine or methylphenidate actually make the task more salient, exciting. The subjects perceive them as much more interesting and that effect, which showed was directly associated with the ability of these medications to increase dopamine in the brain, thus they temporarily compensate for this deficit that individuals with ADHD have.

FLATOW: Does this explain why people with ADHD are at a higher risk for a substance abuse?

Dr. VOLKOW: These could provide an explanation indeed. And in the substance abuse field, it is recognized that one of the variables that makes a person vulnerable to take drugs is a decreased function of the dopamine reward pathways that leads this person in an attempt to auto-medicate, take drugs, which will temporarily increase dopamine in this pathway as a means to correct the deficit. The problem is it's temporary and with chronic repeated administration of drugs that hyper function becomes worse.

FLATOW: Mm-hmm. Some kids drink a lot of, you know, the caffeinated drinks. Is that - was that - is that a self-medication method too?

Dr. VOLKOW: Well, caffeinated drinks will also increase the activity of the dopamine cells. It will increase dopamine release and it will increase dopamine signaling. So, just caffeine will improve performance in individuals with ADHD in part, it's believed, because of its ability to enhance dopaminergic signals.

FLATOW: Mm-hmm. Let me just - well (unintelligible) because I know you're an expert in drug induction. There is a study out in Neuron this week that explores how nicotine creates strong memory associations with the environment. Can you explain how this work?

Dr. VOLKOW: Yeah, this is a fascinating finding. And we've known all along that dopamine is very important in memory and specifically in the type of memory that actually is required to create associations with the environment, which Pavlov coined the term, conditioning. That's a type of memory, conditioning requires dopamine.

And nicotine actually activates dopamine cells through their effects on nicotine receptors. So when you're smoking, you are in the environment and you're smoking amidst your everyday activities. So, the consequence is your brain automatically, unconsciously learns the association of this environment with the experience of dopamine, which is perceived as rewarding salient.

And so, you get conditioned. And the negative part of this conditioning is that when you get exposed to the same environment, this conditioning will lead you to crave the cigarette, in expectation of getting that increasing dopamine. So, it creates a positive feedback loop where upon the memory perpetuates itself by engendering this desire to take the drug. You take the drug that goes dopamine ups. Again that strengthens conditioning next time you get exposed. And these may be one of the reasons why it's so extremely difficult for individuals to stop smoking because their environment is conditioned to the smoke.

FLATOW: Yeah. Yeah. Let me get back to - because I've just a short bit of time left. Let me get back to a question about ADHD. I imagine, you know, we're now in the era of understanding the human genome. I guess the generics of ADHD now would be a big thing to understand.

Dr. VOLKOW: Absolutely. Like any of the other diseases, it's an extraordinary opportunity and studies in - many studies have been done on the genetics of ADHD and two of the most robust findings, actually, are with regards to two genes that regulate dopaminergic neurotransmission, the dopamine transporter and the dopamine D4 receptors. Polymorphisms on them have been linked by several studies with a greater vulnerability for ADHD.

FLATOW: Well, now that you have shown that there is a link between the reward system and the dopamine levels, what do you tell parents or teachers of people who are involved with these kids who have ADHD?

Dr. VOLKOW: Well, certainly I think it is very important, number one, to make them aware that this is a real disorder, because to start with, this has generated an enormous amount of controversy in the field and in the lay public. And this is important for parents because many times they get anguished, and they said should I give a medication to my child because they say they have ADHD?

So recognizing ADHD as a disorder is very important, and this story provides -like others have done in the past - objective evidence of changes in the biochemistry and the function of the brain of these individuals. That's number one.

Number two, by understanding the neurobiology, it gives parents a better comprehension of the behavioral difficulties that their kids have, and the same pertains to a teacher with respect to better understanding why it's so difficult for a kid that has ADHD to maintain their attention and why it is so easy for them to get distracted by novel stimuli.

So it provides an understanding. And the third one, of course, is there that they're at - they're building interventions of this understanding that challenge - put it in other words - of making tasks much more salient for these kids so that they can engage their attention, which, in turn, can maintain the attention and improve the performance. And that pertains both to parents and teachers.

How can you actually give tasks to these kids that will make it salient? Just like a video. I mean, the technology on videos has maximized the ability of engaging the attention, not just of young people, but also adult people. Why can't we use not similar strategies to take advantage of them and facilitate education?

FLATOW: We should find more educational videos or videogames.

Dr. VOLKOW: I think why not? I mean, we have this technology, which is extraordinary. And if we can use it to maximize the likelihood of kids learning difficult subjects or subjects that they may find boring, we should use them.

FLATOW: Well, good luck to you, and good luck with your research coming up.

Dr. VOLKOW: Thanks very much.

FLATOW: You're welcome. Nora Volkow is a director of the National Institute on Drug Abuse at the National Institutes of Health in Bethesda, interesting research showing that you can actually show that there is a connection between ADHD and dopamine levels in the brain, showing that it does exist as a real illness. And people want to know, you know, they talk about it all the time, and we now understand a better way of how it works and maybe how to deal with it.

We're going to take a quick break, and when we come back, Dr. Lawrence Krauss is here to talk. He's a cosmologist, a physicist - to talk about an interesting idea of why don't we make a trip to Mars one-way? Will anybody take a one-way trip to Mars? A lot of people will. You'll be surprised to hear about when Dr. Krauss is here right after the break, so stay with us.

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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR News.

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