How Early Events Affect Growing Brains An interview with Neuroscientist Pat Levitt
Abstract: Recent advances in neuroscience show clearly how experience can change brain neurochemicals, and how this in turn affects the way the brain functions. As a result, early negative events actually get built into the growing brain’s neurochemistry, altering the brain’s architecture. Research is continuing to investigate how children with genetic vulnerabilities, such as autism, schizophrenia, and anxiety and attention disorders, are affected by early experiences, and the relationship between brain chemistry the expression of these genes. But the science is clear as it relates to public policies: from a neuroscience perspective, it is far better to prioritize early supports that promote positive social and emotional development in children than to wait until the problems occur and try to fix them.
We know that things can “go wrong” in the developmental process. What are the dangers to the growing brain and what happens when the dangers are present?
Much of what represents a threat to healthy brain development involves what we call toxic stress resulting from chronic negative experiences or threats both to the immature stress-hormone system and even certain developing circuits of the brain itself. These stressors may include, but not be limited to, child abuse and neglect. And we now know that the presence of these stressors can change brain chemistry very specifically. First of all, it can change the kinds of proteins and other molecules that are actually produced by the brain. And we know that those changes, in turn, can change brain architecture at a very fine-grained level. The level we’re talking about is comparable to, say, changing some very specific details of how a computer’s circuit board is wired up. It’s not like we’re pulling the entire circuit board out of the computer; the changes happen at a microscopic level.
So stress affects the developing brain sequentially. First, the stressor changes the actual neurochemistry. And these chemical changes can then change the brain’s physical structure. Imagine adding something to the soil of a rose plant that stunts its growth and prevents it from reaching its full potential. A number of things might happen: The rosebush could grow shorter. It could produce fewer flowers, or smaller ones. And so on. Well, the same principle applies when we’re talking about a developing child: Changing his or her brain chemistry would actually change the brain’s architecture in a way that is likely to inhibit the child’s ability to develop and flourish the way he normally would.
Importantly, the harm we’re talking about can arise in two ways. Take our rosebush again: You can harm the plant by withholding its food and fertilizer, for example, or by adding something damaging to its surroundings. So in the human, so-called toxic stressors can be the absence of good, nurturing experiences during important stages of development, or severely negative experiences—child abuse, obviously, or environmental dangers like mercury or lead. Anything that interferes with the normal relationship between the individual and his or her environment can threaten this process of healthy brain development.
If stress can impair the brain, what can enhance its early development?
We know, for example, that a child who grows up with adults who use more complex language will quickly develop the ability to use more complex language herself. And we know a lot about the effect of “enriched” environments on human brain development, and how stimulation of the sensory systems—touch, sight, even olfactory—has a direct, positive impact on both brain architecture and brain chemistry. By positive, I mean the connections develop better; the chemistry is established in a way that allows these systems to function better.
Please tell us a bit about your current research interests at the Kennedy Center for Human Development at Vanderbilt University.
My lab is really interested in how early experiences—both pre and post-natal experiences—impact brain architecture and brain chemistry, and how these can be impacted by genetic vulnerabilities. We’re looking at autism, schizophrenia, and anxiety and attention disorders. What we want to get to is, even if you have a specific genetic vulnerability to one of these conditions, isn’t there some intervention we can develop that can help circumvent that vulnerability to make your range of early developmental experiences count even more? Let’s say you’re carrying a genetic mutation that doesn’t cause one of these disorders but [it] puts you at risk. We’re trying to understand how the balance of your genetic vulnerability and your varied experiences early in life interact with each other—and influence the chances that you’ll succumb to the condition. Take autism, for example. Studies of identical twins have shown that when one twin is autistic, the other has the disorder 70 percent of the time. That suggests that there’s certainly a component that’s inherited—but since the correlation isn’t absolute, we know something else [in the environment] has to have been involved. That’s where neuroscience is still evolving on the cutting edge, and the implications are huge. If we can better understand this question of susceptibility in the conditions we’re studying, the knowledge can translate into a whole range of developmental disorders.
Like your colleagues on the National Scientific Council on the Developing Child, you see a gap between what the science tells us and what our public policies aim to do. Where do you think this gap is most pronounced?
As a general matter, I believe our public policies underestimate the overwhelming influence of early experience on brain development. And that gap is reflected in the way we prioritize our national resources. If you add up the dollars we put into intervention programs like drug and alcohol abuse and criminal remediation, for example, and compare that to what we invest in early environmental supports that promote positive social and emotional development—I don’t know what the exact ratio will be, but it will reflect an enormous gap with our scientific knowledge base. We know from the scientific evidence that the greatest impact we can have is to invest very early, during these sensitive periods when the brain is most plastic or malleable. Yet we continue to invest economically in people at a time when it becomes more and more difficult to make a difference and to alter their life trajectory. Unfortunately, it’s as if we’ve taken the approach that we’ll just wait until the problems occur and then try to “fix” them. Well, from a neuroscience perspective, that’s exactly what we don’t want to do.
The field of neuroscience is advancing at lightning speed. What do we know today that we didn’t know a few years ago, and how has that affected your work?
Some of the most important advances involve the way we can now literally watch the brain in action. For example, neuroscientists have used experiments with animals to identify some mechanisms [to ascertain] how a toxic stressor—say, poor maternal care—actually changes the architecture of her offspring’s brain. And we can see the way it cranks up the stress hormones in the animal’s body as it is developing. In the work we’re doing here, I can identify how early experience changes the brain’s neurochemicals, and how the changes affect the way the brain functions. I can identify specifc genes that change; I can even identify how those specific genes are modified over the course of this process. Taken together, that lets us tell you how early negative events actually get built into the growing brain.
We’ve sort of punched through to the “black box” [to use an aeronautical investigator’s terminology] and uncovered a lot of important mysteries as a result. And a lot of this has happened in maybe the last five years—since the late 1990s. Before then, we could only observe that a child was exposed to severe stress and the brain seemed different as a result, but we couldn’t draw a direct causal effect. I think the real breakthrough has come with our ability to monitor brain changes with specific experiences. At Vanderbilt, a colleague is studying patterns of brain activation in children—using some of the same “hot spot” technology you’re familiar with from the Weather Channel—to watch what happens to the brain as an intervention occurs for kids with math and reading problems. It provides a window into what’s happening as the child thinks and reasons through a problem.
If information like this [continues to be] produced in the next ten years, it will be an incredibly exciting and promising field with implications for all sorts of domains and human disease.