For decades, scientists have assumed that the brain circuitry for social behavior has developed over millions of years of evolution and is hardwired at birth. Based on this view of human development, we all start life with the same basic brain wiring, and our uniqueness is built upon that common biological foundation.

That assumption is challenged in a paper released Monday by neuroscientist Lisa Feldman Barrett, who suggests that babies are not born with the circuitry for social behavior. Instead, that circuitry is created during infancy and childhood as the brain wires itself in response to caregivers, culture, and social environment.   

“The infant brain is not a miniature adult brain; it needs wiring instructions from the world,” said Barrett, a University Distinguished Professor of Psychology at Northeastern.

The paper, which was co-authored with Barrett’s postdoctoral fellow, Shir Atzil, and researchers from Hebrew University in Jerusalem and the Cedars-Sinai Medical Center in Los Angeles, was published in the journal Nature Human Behaviour.

The paper lays out a new framework for understanding social behavior, which Barrett said could represent a paradigm shift in the field of developmental neuroscience.

“It’s not a single hypothesis, but a whole framework that guides the questions researchers ask, the experiments they perform, and how they interpret data,” she said. “We’re replacing the old framework with a new one that has new and better questions.”

This new framework could have far-reaching implications.

For example, it asserts that human brain circuitry is not identical. The microwiring in each brain is created in response to experiences during infancy and childhood. So a child’s brain will develop differently depending on how attentive her parents are, whether she lives in poverty, and which culture she grows up in.

Early infancy is a critical time for establishing the biology of a healthy mind. You’re not born with a social brain, you grow one.

Lisa Feldman Barrett, University Distinguished Professor of Psychology

“Empirical evidence suggests that not all mental and social capacities are universal and deep cultural differences exist between groups,” the authors write. “Emotional and social concepts are environmentally constructed in each culture, and these cultural differences become biologically embedded in brain structure.”

This leads to another significant implication—that childrearing and early childhood experiences are more important than we thought. Not only do early experiences shape our personality and values; they also create the wiring that will govern our perception of the world far into adulthood.

Barrett emphasized that even in the new framework, there are significant commonalities in human brains, regardless of geographic location and social position. One key is that the quality of early life experiences plays a much larger role than commonly thought in the adult health of individuals.

“We’re not all snowflakes,” she said, referring to the notion that no two are alike. “Were more like houses; we can only weather strong storms if we’re built on a solid foundation.”

Growing a social brain

Barrett and her co-authors base their theory on an extensive review of existing research in the fields of brain imaging, brain development, and the neurobiology of social development in animals.

“Taken together, these lines of research [indicate] that the idea we are prewired for social bonding is not well supported by empirical evidence, and there is a need for an alternative theoretical framework,” said Barrett.

This new framework still credits evolution with imbuing the newborn brain with several universal qualities. First is the extraordinarily long time that infants remain dependent on their caregivers. This, in turn, results in a powerful biological incentive for the infant to become attached to those caregivers so they can learn how to survive in the complex social world more effectively.  

At the center of this biological survival instinct is a process called allostasis: a sort of biological efficiency that must be achieved in order to survive in a gamut of stressful situations. Allostasis rewards behavior that replenishes energy and, in response to stressors, allocates those resources efficiently. During early development, infants rely on caregivers to maintain allostasis for them by providing the proper food, temperature, and social contact.

Barrett contends that the brain’s primary function is not thinking, but anticipating the needs of the body and meeting those needs before they arrive. This is how allostasis is maintained efficiently.

“Your brain is running a budget for your body,” she said. “Instead of budgeting money, it’s allocating resources like water, salt, and glucose. You can think of your brain as your body’s chief financial officer, moving resources around to achieve the best results.”

Because infants are incapable of doing any of these things on their own, they are entirely dependent on their caregivers. Their survival depends on forming close bonds with those caregivers and eventually learning their way of perceiving and functioning in the world.

As we grow into more independent social beings, maintaining allostasis becomes far more complex and requires a highly sophisticated social brain.

“Humans can never bear their allostatic burden on their own,” said Barrett. “We help each other manage our body budgets, friend to friend, parent to child, partner to partner.”

In the highly interdependent world of humans, no one is an island. To thrive, we need a highly sophisticated social brain, she concludes.

The authors suggest that their new framework for human development has potential implications for understanding health, mental illness, education, and more.

“Early infancy is a critical time for establishing the biology of a healthy mind,” said Barrett. “You’re not born with a social brain—you grow one.”