In 2025, a major review called ‘The Evolving Neurobiology of Early-Life Stress’ was published in one of the leading neuroscience journals, Neuron. This paper, written by Birnie & Baram*, brings together recent research on how early experiences shape the developing nervous system and why the effects of early stress can persist over time.

The authors emphasise that early stress matters not because a child consciously “remembers” specific events, but because the capacity of the nervous system to regulate stress is being formed in early life. Infancy and early childhood are periods when regulatory systems are still developing. During this time, children cannot calm themselves independently or manage states of arousal and distress; they rely entirely on their environment and on adults around them.

A central distinction in the review is between acute stress and what researchers describe as chronic activation. Acute stress refers to a short-term response in which the body becomes aroused and then returns to a calmer state. This kind of stress, in itself, is not harmful. In fact, it can support healthy development by allowing the nervous system to learn that arousal can be tolerated and resolved.

Chronic activation, however, is different. It refers to a state in which arousal does not come to an end. The body remains on high alert, recovery is limited, and tension becomes the background state. The authors highlight that repeated experiences of unresolved arousal in early life can have a lasting impact on how regulatory systems develop. As they note, early experience “does not simply influence stress responses, but shapes the architecture of developing regulatory systems, determining their later sensitivity” (Birnie & Baram, 2025).

This is particularly relevant for adopted children. Many have not necessarily experienced single, dramatic traumatic events, but rather loss, instability, unpredictability, or the absence of a consistent caregiving adult early in life. From the perspective of the developing nervous system, these experiences can register as ongoing stress without sufficient opportunities for recovery. In such conditions, the body adapts: it learns to function in a state of heightened activation because no alternative pattern has been established.

Importantly, the authors stress that infants and young children do not interpret experiences in the same way adults do. What matters most to the developing brain is not how “serious” an event appears, but whether arousal is followed by comfort, calming, and restoration. When this does not happen consistently, regulatory systems are shaped in a way that leaves them more sensitive and less flexible later on.

The article does not describe this process as irreversible damage. On the contrary, it highlights the ongoing plasticity of the developing brain. At the same time, it makes clear that when early stress affects the formation of regulation, its impact is seen not in memories of events but in how the nervous system functions—how quickly it becomes activated, how difficult it is to settle, and how intense emotional and bodily reactions can be.

For adoptive parents, this research offers an important framework for understanding their child. Many difficulties—strong emotional reactions, heightened anxiety, problems with calming, or, conversely, emotional withdrawal—are not signs of personality or deliberate behaviour. Rather, they can be understood as the biological imprint of early experience on the developing nervous system, a pattern increasingly recognised and described in contemporary neuroscience.

Reference

*Birnie, M. T., & Baram, T. Z. (2025). The evolving neurobiology of early-life stress. Neuron.
https://www.cell.com/neuron/fulltext/S0896-6273(25)00134-5

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