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.

Council Member Pat Levitt is Annette Schaffer Eskind Chair and Director of the Kennedy Center for Human Development at Vanderbilt University. He studies the molecular and cellular mechanisms that control the development of the brain, and the causes for developmental and neuropsychiatric disorders such as autism, anxiety, and schizophrenia. He is a member of the Research Network on Early Experience and Brain Development. He is the senior editor of the Journal of Neuroscience, a chairman of the Scientific Advisory Board of Cure Autism Now, and a member of the Scientific Advisory Board for the National Center for Toxicological Research. He earned a Ph.D. in neuroscience from the University of California, San Diego, and completed a postdoctoral fellowship at Yale University School of Medicine.

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.

If stress can impair the brain, what can enhance its early development?

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.

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.

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