how connection developsEarly care becomes part of a child's experience through feeding, touch, voices, and responses to what they need. Research has examined these experiences at several biological levels, from the activity of individual genes to the development of larger brain systems.
In their 2018 perspective paper, Growing a social brain, Shir Atzil, Wei Gao, Isaac Fradkin, and Lisa Feldman Barrett proposed that dependence on others for bodily regulation helps drive early social learning. They used the term allostasis for the body's ongoing adjustment to its needs, including anticipating what comes next. Their supplementary evidence table brings together studies of how early social experience relates to development. Those studies make the biological significance of care more concrete, while differing in what they can establish.
This is a theoretical synthesis, rather than a new experiment with one group of infants. Its central proposal is that care helps make other people meaningful because their presence repeatedly accompanies changes in bodily needs. The individual studies provide evidence about parts of that process. They do not yet establish the whole proposed pathway.
A brain developing through experience
The supplementary table spans several kinds of change. Some studies examined receptors, the proteins through which cells respond to chemical signals. Others examined gene activity, substances involved in neural growth, the structure of particular brain regions, or connections among larger networks.
These are different observations. A change in a hormone receptor is not the same as a change in brain volume, and neither tells us everything about a child's experience. Taken together, however, they show why the biological study of development includes the conditions in which an animal or child receives care.
The table also includes research showing that large-scale patterns of brain connectivity continue to develop after birth. Networks involved in adult cognition acquire their mature organization over time. This developmental evidence identifies a period in which experience and maturation occur together. By itself, it does not settle how much of a network's eventual organization depends on inherited biology or particular experiences.
The authors focus on the default mode and salience networks, which participate in social experience but also support other functions. Their argument is not that a separate social organ appears through care. They propose that systems involved in making sense of experience and regulating the body also become resources for relating to other people. They explicitly acknowledge that a developing network could still have an inherited basis. Plasticity alone cannot decide between competing explanations of how social capacities emerge.
What animal studies reveal about care
Some of the clearest opportunities to separate early care from biological inheritance came from studies of rats. Mother rats naturally varied in how much they licked and groomed their pups. Researchers could observe those differences and, in cross-fostering experiments, arrange for pups to be raised by a mother other than the one that gave birth to them.
The supplement describes research by Frances Champagne and colleagues in which female offspring born to mothers that provided less licking and grooming were fostered at birth by mothers that provided more. Their later levels of a particular estrogen receptor in a brain region involved in maternal behavior reflected the care they received. Moving pups in the opposite direction produced the opposite pattern.
Changing the caregiving environment made it possible to examine something that an ordinary family resemblance could not resolve. The similarity between generations involved the experience of being raised as well as biological inheritance. In these animals, differences in care reached the machinery through which brain cells responded to hormones.
Other studies summarized in the table linked higher levels of early licking and grooming with smaller hormonal responses to acute stress and differences in receptors involved in regulating that response. These findings concerned specific animal populations and measurements. They help explain possible biological pathways through which care has lasting effects, rather than providing a formula for human parenting.
How experience relates to gene activity
The supplement also describes epigenetic findings. These concern processes that influence how genes are used. They include chemical marks on DNA and changes in the way DNA is packaged. A difference in gene activity does not require a change to the inherited DNA sequence.
In the maternal-care research, investigators examined how such processes related to the production of receptors involved in stress regulation and maternal behavior. This connected an observable experience, the care an animal received, with a measurable difference in how its biology operated.
The table includes findings from adverse early experiences too. Studies of maternal separation in animals and childhood maltreatment in humans examined differences in stress-related biology, growth factors, and brain structure. The human findings included observational and postmortem research, which cannot separate every influence on development. Their contribution is to show associations that require explanation, alongside animal experiments that can examine particular mechanisms more directly.
Hearing a familiar voice before full-term birth
A human experiment listed in the supplement examined a specific part of the sensory environment. In a 2015 study by Alexandra Webb and colleagues, 40 infants born prematurely were randomly assigned to receive recorded maternal sounds or routine hospital sound exposure. The recordings combined each mother's voice with her heartbeat.
At approximately one month of age, ultrasound measurements showed a thicker auditory cortex in the infants who received the recordings. The auditory cortex is involved in processing sound. The study demonstrated a structural response to this particular sound experience during early development. Whether that difference would translate into later language or other developmental benefits remained to be established.
The comparison concerned sounds normally available during pregnancy and the different auditory environment of a hospital. It made one part of early experience specific enough to investigate.
Support and brain development across childhood
Another study in the supplement followed children over time. Joan Luby and colleagues observed maternal support during the preschool years and later measured the children's hippocampal volumes at school age. The hippocampus is involved in memory and stress regulation.
Greater early support predicted larger later hippocampal volumes, with a stronger association among children who had not experienced preschool depression. Because support was observed rather than randomly assigned, the study established a relationship across time rather than isolating care as its sole cause. Shared genetic and environmental influences remained possible.
This finding concerns a particular brain region in a particular developmental context. Its contribution is the connection between an earlier observation of care and a later biological measure. It adds a human developmental timescale to the animal and infant studies assembled in the paper.
Learning what to expect from another person
Atzil and colleagues proposed that repeated care connects the sights, sounds, and touch of a caregiver with changes inside an infant's body. Over time, those experiences could help an infant learn whom to approach and what to expect. They extended this account to shared attention and learning within a family and culture. The proposed mechanism remains a theory, alongside the specific findings it seeks to explain.
Feeding offers a concrete example of the proposed learning. The sight, sound, and smell of a caregiver occur alongside changes in hunger and nourishment. The authors suggest that repeated experience allows these outward cues and inward changes to become linked. Eventually, a familiar voice or face could help an infant anticipate care, rather than being only another sight or sound. The paper illustrates this with a predictive model, not a direct measurement showing that this entire sequence has occurred in an infant's brain.
The caregiver in this account is defined by the relationship, not by a particular gender or biological tie. The authors use the word mother in many examples but explicitly extend their proposed learned caregiver concept to fathers and other caregivers. What matters to the theory is the repeated association between that person and the care they provide.
From being cared for to sharing attention
The paper also considers how these early exchanges could become a foundation for learning with someone else. Synchrony involves coordinating timing, as when an infant and caregiver adjust their voices, movements, or attention in relation to one another. Joint attention adds a shared focus on something beyond the two people. In the authors' account, a caregiver can help bring part of the world into view, and shared attention becomes a setting for learning words, meanings, and the practices of a community.
This extends the importance of care beyond settling an immediate bodily need. The proposed benefit is a growing capacity to anticipate, participate, and learn with others. These connections between bodily regulation, brain networks, and social learning are questions the framework invites researchers to test, rather than a finished explanation of every child's development.
The authors give early life particular importance while also describing social learning and bodily support as continuing throughout life. This is not a claim that one difficult period determines a person's future. Nor does the paper establish that a particular caregiver caused a child's developmental differences. Its account places relationships within a larger developmental process that also includes inherited biology and the conditions surrounding a family.
The studies give care a physical context. A voice is also sound reaching a developing auditory system. Touch is also sensory input. Support occurs while the systems involved in memory, stress, and learning continue to develop. The ordinary ways people care for a child are among the experiences through which that development takes place.
Sources
Atzil, S., Gao, W., Fradkin, I., & Barrett, L. F. (2018). Growing a social brain. Nature Human Behaviour, 2, 624–636. Includes Supplementary Table 1. Author manuscript. Author correction. The correction changes two reference citations in the predictive-processing discussion, rather than reporting a new experiment or revising the central proposal.
Champagne, F. A., Weaver, I. C. G., Diorio, J., Dymov, S., Szyf, M., & Meaney, M. J. (2006). Maternal care associated with methylation of the estrogen receptor-α1b promoter and estrogen receptor-α expression in the medial preoptic area of female offspring. Endocrinology, 147(6), 2909–2915.
Webb, A. R., Heller, H. T., Benson, C. B., & Lahav, A. (2015). Mother's voice and heartbeat sounds elicit auditory plasticity in the human brain before full gestation. Proceedings of the National Academy of Sciences, 112(10), 3152–3157.
Luby, J. L., Barch, D. M., Belden, A., Gaffrey, M. S., Tillman, R., Babb, C., Nishino, T., Suzuki, H., & Botteron, K. N. (2012). Maternal support in early childhood predicts larger hippocampal volumes at school age. Proceedings of the National Academy of Sciences, 109(8), 2854–2859.