'Serve and Return' Interactions Key to Babies’ Brain Development

Resilience is a skill that children learn through nurturing, experts told a AAAS audience.

From birth to age 2, babies' brains are pre-programmed to undergo remarkable changes, forming 700 new synapses per second, yet the successful development of brain architecture requires continuous nurturing by caring adults, experts said on 18 June.

"Children learn best when they are close to an adult," said Pat Levitt, one of three speakers at the latest Neuroscience & Society event organized by AAAS and The Dana Foundation. "They are not passive sponges, to be set in a room to absorb information."

Babies' brains develop in response to genetic factors as well as early experiences, and in particular, "serve and return interactions" — such as what happens when a child coos and a parent responds, said Levitt. He is the Simms/Mann Chair in Developmental Neurogenetics at the Institute for the Developing Mind, Children's Hospital, and WM Keck Provost Professor of Neurogenetics at the Keck School of Medicine, University of South California.

Too often, Levitt said, American parents seem to believe that "bad stuff happens," but children who are "rugged individualists" will succeed in life, no matter what fate throws their way. In fact, he said, "Genes and experiences together build brains," largely through positive interactions with caring adults. "Cognitive, social, and emotional development is inextricably intertwined."

Resilience is not an inherent trait, Levitt added, but rather, a skill that children must learn, while toxic stress such as neglect or abuse can damage children's brain architecture, making it more difficult for them to overcome future challenges. He cited a Science paper by Edward F. Chang and Michael M. Merzenich, who found that laboratory rats subjected to a "white-noise" environment could then only hear those sound frequencies. In humans, Levitt said, language skills develop when adults tell babies the names of objects, and later, when they use books to show that words can be represented by marks on a page.

While emphasizing that all babies are unique, and therefore "normal development" can vary, AAAS speaker Lisa H. Shulman, M.D., of the Albert Einstein College of Medicine described the key milestones of early childhood. Newborns are "pre-programmed to grow, move, vocalize, socialize, and learn," she said, but their movements are initially reflexes, which prompt their fingers to curl around a parent's thumb, for example. To further develop, newborns' brains require stimulation from caring adults. "Babies are born with social capability," Shulman said, noting that a newborn's eyesight is designed to focus on nearby objects such as parents' faces. "They prefer to look at faces and listen to voices over other stimuli. They match facial expressions."

By 2 months of age, Shulman said, a baby will begin to smile, track objects, and vocalize. By the fourth month of life, a baby has head control and can swipe at objects. Between 5 and 9 months of age, she will learn to sit and respond to her own name. Between 9 and 12 months, Shulman continued, the baby will begin to pull herself upright, crawl, point at what she wants, use her first words, and follow verbal commands such as, "We're going bye-bye," even without the help of parents' gestures. Most children begin to walk between 12 and 18 months, and by 24 months, Shulman said, their 200-word vocabulary is rapidly expanding; they are then "playground ready" — climbing stairs, kicking and throwing balls, and jumping.

Young children may hit each developmental milestone at slightly different ages, but they should attain each skill in order, said Shulman, who is an associate professor of pediatrics and director of the Infant/Toddler Team at the Rose F. Kennedy Center Children's Evaluation and Rehabilitation Center. For example, she said: "If we see a baby that cannot respond to his or her name at 15 months, that will be a concern," since it could be a sign of autism, if hearing problems have been ruled out. Similarly, a 24-month-old toddler who can climb down the stairs but not up the stairs should be screened for muscular dystrophy, Shulman said.

Understanding the complex process of human development, from birth to old age, is the focus of the U.S. National Institute of Child Health & Human Development (NICHD). Currently, the NICHD provides $900 million per year in research grants. Lisa Freund, M.D., chief of the NICHD's Child Development and Behavior Branch and a speaker at the AAAS event, estimated that about 10% of all NICHD external grants focus on research to better understand the development of babies up to age 2. Many of those projects relate to physical and medical conditions that can affect children, but other research is looking at language, cognitive, brain, social, and emotional development, as well as nutrition and many other issues. She noted, in particular, that the NICHD earlier this year issued a funding opportunity announcement for researchers studying babies' connectome-the "wiring diagram," or map of neural connections in the brain.

[Credit for associated teaser image: Wikimedia Commons/Reverie Zurba/USAID]