Well before young children arrive for the first day of school, their brains have undergone an extraordinary process of development. At birth, the brain weighs about 400 grams and has 100 billion neurons. By the age of 2, at 1100 grams, it is about 80% the size of an adult brain. At some early stages of development, the brain is adding up to a half-million neurons per minute, and by age 3, it in will have 1000 trillion neuron connections.
Today, technological advances such as functional Magnetic Resonance Imaging (fMRI) are giving researchers a window onto the deepest structures and most complex functions of the brain. That’s allowing neuroscientists a detailed new understanding of how a stimulating environment and a sense of security in early childhood can be critically important for healthy brain development.
Research is also creating new insights into what can go wrong. At a Capitol Hill briefing organized by AAAS, neuroscientists described how conditions associated with poverty—including a lack of nurturing and high levels of stress—can set off a cascade of neural and hormonal responses that disrupt brain development and have negative impacts on language, learning, and attention.
The new research is shedding a different light on the effects of poverty, and raising critically important questions for communities and policymakers in areas ranging from education and health to social welfare and juvenile justice. Scientists have long known that poor nutrition or exposure to lead could affect brain development, but could a lack of books or an excess of stress be similar cause for concern?
“Where a child grows up in impoverished conditions… with limited cognitive stimulation, high levels of stress, and so forth, that person is more likely to grow up with compromised physical and mental health and lowered academic achievement,” said Martha Farah, director of the Center for Neuroscience and Society at the University of Pennsylvania.
“The promise of neuroscience is to understand how this works,” Farah added, “so that you can intervene” to help families and communities provide a better environment for children.
The 90-minute briefing, held 26 June, drew an audience of over 100 people, including congressional staff, federal scientists, and journalists. It was held with the support of U.S. Representatives Chaka Fattah (D-Pennsylvania) and Brian Bilbray (R-California), and was the first in a series of three Capitol Hill briefings on neuroscience organized by the AAAS Office of Government Relations and underwritten by The Dana Foundation.
In addition to Farah, the panel included James Griffin, director of the Early Learning and School Readiness Program at the National Institutes of Health, and Annapurni Jayam-Trouth, chair of the Department of Neurology at Howard University, who served as a discussant. The briefing was moderated by Alan I. Leshner, the AAAS chief executive officer and executive publisher of the journal Science.
Leshner, a neuroscientist, said that much research remains to be done to understand the interplay of factors shaping childhood brain development. But he called the new insights “exciting” and said they provide a valuable example “of how an emerging body of scientific literature really can in fact help us to develop far more effective social programs and programs intended to better the lives of all children.”
Fattah is the author of the Fattah Neuroscience Initiative, signed into law last November by President Barack Obama to establish a high-level, interagency working group to coordinate and advance federally funded neuroscience. In remarks that introduced the researchers’ presentations, he cited the potential of neuroscience to create understanding and treatments for conditions ranging from mental illness to traumatic brain injury.
“It’s critically important that we focus in a much more robust way to move this research area forward,” Fattah said. “It portends a great deal for our country and our world.”
The End of “Nature vs. Nurture”
American culture venerates the ideas of free will and self-determination, and tends to view poverty as a mark of flawed character and moral weakness. That has been the backdrop for a long-running debate in science, and throughout much of American social and political culture, over whether child development is shaped more by genetic factors or environmental factors.
But at the AAAS briefing, findings discussed by the researchers challenge some old paradigms. Put simply: It’s not nature vs. nurture—it’s a constant interplay between the two.
Genetics may shape the response to environmental conditions, and stimulus from the environment can influence genetic responses for better or for worse. Understanding that is essential to understanding early brain development, Farah and Griffin agreed.
In its earliest growth, Griffin said, the human brain is developing its basic components and functions—for example, the primal “fight or flight” response to a perceived threat. Even from an early age, infants show signs of awareness, recognition of ambiguity, and an ability to solve problems. But brain areas such as the prefrontal cortex that govern more complex functions—language, problem-solving, self-regulation, and social bonding—tend to develop later, between the ages of 1½ and 4 years.
“This really is a crucial period in brain development,” Griffin explained. “We know we need to… take full advantage of what we can do for children (at that age) so they reach their full potential.”
Separate from neurons, neural connections have their own significance. “It’s not just the neurons,” Griffin said. “It’s how they connect [with chemical neurotransmitters] and fire together that we’ve learned is the most important” to assisting brain functions—and impeding them.
Between birth and the age of 3, he said, the brain produces an excess of neurons and neural connections. But waves of neural growth are followed by periods of “pruning” in which neurons and connections that are not being used are, in effect, taken off-line.
“It’s a use-it-or-lose-it process,” he explained. “If something isn’t being used, if it doesn’t become part of the circuitry, it basically is pruned off. Those neurons go away. Connections aren’t made.”
The Powers of Nurturing and Stress
That process of building connections points to the importance of cognitive nurturing. When parents or caregivers spend time talking or reading with a child, the intellectual activity stimulates the brain, helps to activate and build neural connections that link different parts of the brain. Without engagement, those connections may be diminished or lost.
But stress is a sort of counterpoint to nurturing. Stress, too, is a sort of stimulation, and as a part of everyday life, it isn’t always bad. But it can be disruptive to both parent-child relationships and children’s learning, especially if it is overwhelming and chronic.
“Stressful lives can cause parents to engage less with children,” Farah said.
Sometimes stress results from the lack of appropriate stimulation, like boredom, or it can arise from excess or inappropriate stimulation. In some homes, Griffin added, there are few books, perhaps because they’re too expensive. But “the TV is on all the time, at really loud levels. It’s inappropriate content for a child, but it’s literally so loud that the child pays attention to it anyway, even though they have no idea what’s going on.”
“Remember all those primitive things, like ‘fight or flight’?” he asked. “When you’re in a stressful overload situation and you’re a very young child, it just becomes overwhelming. And when you don’t have a parent to help mediate the stress, it’s even more so.” In those conditions, learning—and neural connections—may be disrupted.
Stress causes the body to produce the hormone cortisol, and at high levels the stress can become toxic, Griffin said. That can have a direct impact on development of the pre-frontal cortex, which is the seat of attention, judgment, and self-control. The effect, Griffin said, is “disregulating.”
Such stress leaves a physical signature that can be seen on functional brain imaging. Farah said her lab and others are finding that higher income levels are associated with greater volume in the prefrontal cortex and in the hippocampus, a center for memory and learning.
Related studies suggest disparities in brain function between low-income and higher-income children. Farah cited “highly robust, sizeable differences” in the functions of these areas, affecting language, self-regulation, and working memory.
Other research, Farah said, shows that nurturing can offset the effects of stress, in effect making the child more resilient. Consider one study on relationships among mother rats and their pups: Those “reared by extremely solicitous, nurturing mama rats, grow up to have better memory and better stress responses,” Farah told the briefing. “They’re better able to handle stress. And this is true especially when rat pups are stressed.”
For rats as well as humans, the implications are that levels of nurturing can have a direct bearing on the hippocampus, which in turn has an impact on memory and learning. Those two systems are crucial to a person’s long-term well-being.
There’s a specific issue for policymakers that arises from these findings. As Griffin noted: “The psychological stress associated with growing up in poverty can impair early learning abilities, affecting school readiness skills.”
Solutions in Parenting and Policy
Both Griffin and Farah emphasized that the brain can recover from effects of childhood poverty. But, they said, preventing harm is more efficient than repairing it.
“We continue to learn throughout our lives,” Griffin said. “The brain is also able to make new connections after trauma…. At any age, you can learn a new language, you can learn a new skill…. This is one of the things we know with education: If you don’t master things early on, trying to learn it later requires even more—and even more costly—efforts, and even remediation. That’s another reason why intervening early makes all the sense in the world.”
Early experiences promote healthy brain development in areas that affect language, memory, learning, judgment, and emotional well-being. “Research says that everyday experiences with parents and other adults can optimize development in these areas,” Griffin said. “The experiences that children have with their environment, and with people in their environment, especially their parents and other caregivers, really shape this process.”
The simple answer, then, lies in parenting skills practiced at home and in early education: talking, reading, nurturing. Griffin described the familiar picture of a parent reading to a child. Even when the child is very young, a parent might sit and read from a floppy cloth book. “The infant doesn’t know it’s a book—they don’t know what you’re doing is reading,” he explained. “At most, the infant may mouth the book.”
But the infant is learning motor control and language; from a parent’s modeling, the infant or child is learning what a book is, how to hold it, and the joy of reading. As the child grows older, she may begin to turn the pages, describe the pictures, and pretend to read. From repetition of this process, a sense of mastery begins to emerge. And with mastery comes a desire to learn more. The process of this “scaffolding,” or supporting learning, he said, results in a brain that’s healthy and ready to learn more.
For children, the future “depends on us understanding really, fully, what is the science… and how do we put it into practice,” said Trouth, the chair of neurology at Howard University. “The science must be transmitted via many channels of education to the general public, especially to low-income communities, so intervention can begin early, at home.”
Clearly, however, the new research has important policy implications, for helping to address poverty-related issues and, perhaps, for helping to break the cycles that sustain poverty. Turning the new insights into productive policies is almost certain to cause political objections.
In Farah’s view, that’s where neuroscience can play a constructive role in helping to engage policymakers and the public.
“At this point,” she explained, “we are able to study and understand the development in the brain of things like executive function, memory, and language, and we can begin to apply it in domains as diverse as early childhood education, juvenile justice, and policy for poverty alleviation.”
Could neuroscience create more neutral ground for discussing such policy? That’s her hope. “The science is fascinating. I think it can engage people with the awesomeness of brain development… and how it emerges from the interplay of genes and environment. It can renew people’s interest in finding solutions. It also helps to replace the morally fraught concepts of effort, trying harder, pulling yourself up by your bootstraps.”
In place of those traditional views is the more dispassionate recognition that neurons “develop differently under different circumstances,” Farah said. That could help shift the policy discussion away from moral judgments to a public health orientation.
Ultimately, Farah suggested, the new science might even bring people together. The insights “affect everybody,” she said. “We’re not just talking about helping the bottom 20% of children below the poverty line. Understanding the effects of stress and cognitive stimulation on brain development can help everybody’s children to fulfill their potential.”
Watch video highlights of the AAAS Capitol Hill briefing on early childhood brain development.