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Friday, May 1, 2009 | Breakthroughs in genetic research and advances in imaging technology have allowed neuroscientists in recent years to make significant leaps in their understanding of how the human brain develops.

Yet the picture is still far from complete, and research is just now beginning to dispel long-held beliefs ranging from the effects of genes and environment on an individual’s personality to how substance abuse changes the structure of the brain.

At the forefront of this research is the University of California, San Diego’s Terry Jernigan. The 57-year-old neuropsychologist, and director of UCSD’s Center for Human Development, is more apt to tell you how much she doesn’t know about the brain than how much she does know.

But she knows a lot. And her insights might someday change how we as a society approach childhood development. Jernigan shared some of these insights — which she has been working toward since the 1980s — during a recent conversation.

Most of your research has focused on how and why we develop into people with different temperaments and characteristics. Do you have an answer to that question?

Well, this is still kind of a deep mystery, to be honest. Human development is so complex, and plays out over such a long period that it is very difficult to sort of come in as a research scientist and try to resolve these complex issues.

And though there have been very lively intellectual discussions about human differences, until recently, it’s been limited how much real scientific data we could bring to it because we really didn’t have the techniques for it. That is changing quite dramatically and in part it is changing, of course, because the improvements in our ability to look at genetic factors, the field of human genetics and genomics is moving so rapidly that there are questions about genetic factors that are much more accessible to us now.

So where does this bring us in regards to the age-old nature versus nurture debate?

We are in a transformative stage. I think that is the only way I can put it. I think that what we are moving to is a different way of looking at these phenomena, which sort of goes beyond that debate. More and more people recognize now that it is not a very meaningful debate. We have moved beyond the stage where we think of a gene as determining a trait. Or even a set of genes determining a trait, so much as genes seem to control the processes that play out.

If that is the case, how come you still see traits that are common among family members?

There is not really any question, any longer I think, about the inheritability of traits. … There is a lot of evidence for the inheritability of personality traits or certain mental characteristics, meaning that if you are closely related to someone genetically, you are going to be more similar on those things.

But I think what has changed is the idea that there are certain genes that make you that way so much as there are genes that control processes and that as those processes play out, often over very long periods of time, and interacting very intensely with other genes and other processes, sometimes — because of a person’s particular genetic composition — there are small biases in that whole complex process. They are very subtle biases, but they are slightly different than the subtle biases in another person’s set of processes.

Explain what you mean by “processes.”

It might have been easier in some sense to have genes determine personality traits. But the evidence shows that the human personality is very complicated. Ways that personalities end up being different will be multiple. Many genes will contribute to that, and many, many environmental influences will contribute to that.

The whole job of the brain is to interact with the environment. Figure out what is going on in the world. Predict what is going to happen in the future. That is what the brain does. So all the processes, they might be under genetic control, but they are all there to respond contingently to what is going on in the environment. If you can’t do that, you can’t survive. That is what your brain is doing for you. So there is no way to separate the subtle differences that may arise from common genetic variations among us.

So what has knowing this information done to our understanding of how children develop?

There is this implicit assumption that there is a normal course of development. And the implicit idea is that all kids kind of follow it. But that is not what the evidence shows. And so let’s say that that is not true. That in fact kids vary quite a lot in how they develop. So here is why it is important. If you have in your head that there is a fixed developmental sequence, and time course, then you begin to think of our job as a society to define the sort of optimal set of environmental and cultural influences — say for example education experiences — that will ensure the best outcomes in children.

Of course that is a very positively-motivated thing. Here is the rub: if there actually are quite different courses mixed up in this population then the optimal set of circumstances for the group as a whole might be quite deleterious to some individuals — it may not only not be optimal for many children, it may be detrimental to some children. Take the standardized curriculum example. The whole idea that the standardized curriculum is the optimal way to improve outcomes in education is based on the idea that all kids will pretty much respond the same way if given the same experiences. But what if that is wrong? And the problem is that because of the way we have tended to do the research, we don’t have the data to answer that question. And it is an important question.

But that is quite a hill to climb for society, to be able to have specialized, individual responses in public education. Are you confident that we will be able to make strides in that arena?

How tolerant are you, if say your supermarket says “we only have one brand of ice cream.” You don’t tolerate that.

You are saying we can’t have this one-size fits all way of nurturing children. What do you see as the future?

One of the first things we have to do is collect the scientific evidence that informs this debate. The reason we haven’t been able to move very far with this is that it has been a he said/she said question. We don’t have the data. The first thing we have to do is collect the data. And the good news is that the new techniques we have — the brain imaging technology for example — allow us to look in detail at the neuroarchitectural differences in the brain the distinguish all of us from each other.

And furthermore, to look in children at the actual course of the biological development of these neural architectures. One question we can answer is how similar is the time course from one child to the next in this course of biological development. Knowing more about that will help us to know how much we could expect to gain by figuring out how to create a more adaptive educational experience for kids?

There has been more talk (and a New Yorker article) recently about so-called “cosmetic neurology” or people taking pills that are meant to treat ADHD and other cognitive disorders in order to be smarter and more focused. What can you tell us about this trend?

My feeling is that it is an understandable instinct. But it is playing with fire. The knowledge of the whole picture of the effect of a drug is so fragmentary. If you focus on a very specific function — take an average group of people, and you give this drug, on average this function will be slightly improved. But again, we don’t know what functions are reduced. We don’t know in that group of people how many people got better and how many got worse.

All we know is that the net effect was positive. So the same issues that I have been talking about affect this issue. And furthermore, the acute effects of drugs and the chronic effects of drugs can be very different. … It is like we are looking at little tips of icebergs peaking out. We don’t know the whole structure yet. A there is a lot of reason to believe that it is a lot more complicated. The brain is an extraordinary elegant thing. And the idea that we could know a little bit about it and tinker with it, and be highly accurate with the outcome I think is a little arrogant. I am not denying that the day is coming when we will be more proactive in sculpting the parameters of our neurosystems … but I think realistically we have to be humble about the enormous complexity of the human brain.

— Interview by DAVID WASHBURN

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