BW: How does the prefrontal cortex work in carrying out all these functions?
AD: That’s a huge question. It seems like one of the things it does for working memory is it sustains the firing rate of neurons during the brief time that you’re holding the information in mind. They’re literally keeping the information active by staying active. You can see if someone remembers something by looking at whether the neurons in the prefrontal cortex are firing or not.
Earl Miller’s work on monkey brains shows that neurons change the direction of their firing to help you think about a problem in different ways, and you can see that change at the neuronal level in the prefrontal cortex when you try a different perspective. How it exercises inhibitory control is more by putting the brakes on lower areas of the brain, so for example with the amygdala screaming because you got really scared, the prefrontal cortex will kind of calm down the amygdala. One of the ways it does the stopping is through the subthalamic nucleus — very important when you need to not respond right away, so you can have a better response than the first one that occurs to you.
BW: How early can these executive functions be seen?
AD: Well, my dissertation, which was ages ago, says you can see it develop at a rudimentary level between 6 and 12 months of age, or more precisely, around 9.5 months. You can see the beginning of working memory, of inhibitory control, and on a very small level, the beginning of cognitive flexibility, which really comes in later than the other two.
I was doing my assessments by having babies reach for things. If you have them just look at things, then it looks like it could be even earlier — 5 months maybe. It begins to develop during the first year of life, which is much earlier than the experts thought — they thought it didn’t do anything during the first year. However, it takes a very long time to fully develop, not until your mid-20s.
BW: You also talk about external versus genetic factors in the development of executive functions. What are some of those?
AD: For external factors, the prefrontal cortex is the most vulnerable area of the brain, so if something isn’t right in your life — if you’re alone, if you’re sad, if you’re stressed, if you’re not physically fit — that delays the development of the prefrontal cortex.
For example, if a child experiences something really awful — a parent dies or the child witnesses some violence, or is picked on at school — that delays the development of executive functions, meaning the development of the prefrontal cortex.
Then there are genetic factors — for example, the COMT gene (catechol-O-methyltransferase). If you have the Met variant of the gene, you’ll have better executive function at baseline but you’re also more sensitive to stress, have a lower pain threshold, and are more vulnerable to mental disorders. So in a situation of mild stress, people who have the Val version of the COMT gene now look better, as they are calmer in the face of stress — they can withstand more stress before it affects the prefrontal cortex in an adverse way.
I’ve said that COMT Vals look like the picture of resilience in a bad situation, but a child who is COMT Met, even though he or she looks really bad, in a bad situation, has the potential to shine even more than the COMT Val if you can get that child in a good situation, because the COMT Met can get the best tuning of the prefrontal cortex. A child who looks like a disaster in one situation can blossom to be amazing, if only you can find a good situation for that child.
BW: You’ve done a lot of writing on the best ways to encourage executive functions, particularly in the classroom — what are some of those ways that we can keep our executive functions actively growing?
AD: You need to train and challenge executive functions — and you need to keep on challenging them. You need to increase the difficulty of executive-function requirements of whatever you’re doing, so the kids continue to develop them, but you also have to work on the things that I talked about earlier — that the child has to feel calm and cared about in the school classroom and, ideally, at home as well.
If you can develop good relationships in the classroom, especially with the child and the teacher, and the child is securely attached at home, that is extremely important for the development of executive functions and the child doing well. You can have the best things for developing executive functions, but if the child doesn’t like it and doesn’t do it much, it’s not going to improve executive functions.
You need something that not only challenges executive functions, but something that will hold the child’s interest and keep them motivated. You really need something that emotionally connects with the child — often, that is something in the arts, but also something demanding physical activity, sports for example. This will grab a child’s passion more than school subjects — but it could be something else. It could be caring for an animal. It could be community service, or working on a larger project for the school that gets the child extremely invested.
An important way to have kids invested in something is to let them have a say in the planning of that, and in the development of that, even at the level of discipline in the classroom. If the kids participate with the teacher at the beginning of the year in putting together a code of conduct, the kids are much more likely to behave in accord with that code of conduct than if it’s just given to them by the teacher.
BW: So essentially, to find their passion. What they’re good at.
AD: Exactly! Finding their passion and something that requires executive functions and keeps on challenging them. Nine times out of 10, it’ll be something that if you’re able to use executive functions for, you’ll do it better.
BW: You’ve also done some work involving attention-deficit hyperactivity disorder. How can using executive functions combat cognitive disorders?
AD: ADHD is primarily a problem with executive functions. Impulsivity, problems with attention and with working memory are all problems with executive functions — so again, working to train them, challenge them, and find something that grabs the child’s passion is the best way to improve executive functions. Meds can help a little bit, but often the right dose for controlling hyperactive behavior can be too high for the prefrontal cortex and executive functions, so you have a child who isn’t making any waves, isn’t hurting anybody, but isn’t getting anything done, isn’t taking instruction. You want to have a safe dosage for the prefrontal cortex and not just for the lower areas that control hyperactivity.
BW: What do you feel is the most significant study that you’ve contributed to in neuroscience, if you had to choose?
AD: I would say two. The body and data that was my dissertation in postdoc, where I really made a paradigm shift in how we thought about the prefrontal cortex, about cognitive development, and about being able to study brain-behavior relationships, early in human life, and that really lead to the field of developmental cognitive neuroscience.
And then my work on phenylketonuria [an inability to metabolize phenylalanine, a condition causing brain and nerve damage] — the work with the animal model and the work with the children, because I showed that people had no disadvantage with executive-function deficits if they were on what was considered adequate treatment, but nobody was listening to that because it didn’t make sense. They couldn’t imagine that if the whole body was getting too much [of the amino acid] phenylalanine, that one area of the brain is affected and nothing else. It didn’t make sense. So I demonstrated the mechanism by which this occurred, and then I demonstrated that if you just put them on a stricter diet, that it could prevent these deficits, and then other people after me showed that it could reverse these deficits. So that was a big deal in terms of improving the lives of all the kids with phenylketonuria. We showed that if they didn’t start them on diets earlier than the norm, they had settled visual deficits, and it was easier to start them earlier — so that helped children not have a small visual problem that they otherwise would have had.
BW: What advice would you have for someone looking for a career in neuroscience?
AD: First of all, I would say you need to follow your passion. You need to have something that really interests you — not go into neuroscience because someone tells you it’s a good field to go into. I think you should also find your own passion in neuroscience and not have somebody tell you what the best field in neuroscience is. I think for graduate school, people should go to a place where there is more than one professor they might be interested in working with — so if one thing doesn’t work out, they aren’t stranded, there’s other people they can work with. I also prefer in graduate school that the students be allowed to work on a project that is their own idea — as opposed to a piece of a project that is their adviser’s idea or that an adviser tells them to carry out.