Stories of children separated from their parents at the U.S.-Mexico border have spurred outrage around the country and the globe.

On Wednesday, an executive order was signed to end the policy that health experts decried as inhumane and potentially damaging. Families will only be reunited only in federal custody while awaiting prosecution for illegal border crossing, however.

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Beyond the immediate trauma, these forced separations, and the lack of familiar surroundings or other trusted adults, may have serious, long-term effects on the children, says Jacek Debiec, M.D., Ph.D., a University of Michigan psychiatrist and neuroscientist. His research focuses on how rodent pups' attachments to their mothers affect the pups' brains — and he also helps treat traumatized children.

Neuroscience research and observations from treating other traumatized children suggest that their brains, behavior and futures could be dramatically altered, he says. Debiec answers questions about the issue here.

What do we know about the potential effects of separation from parents at an early age?

Debiec: A great deal of laboratory neuroscience research, including my own, has focused on the impacts of early life adversities on the developing brain. And maternal separation, separation of the young from the mother, is one of the more drastic adversities that's been studied. We know it can produce changes that are profound and long-lasting. That's what makes the decision to address a current political issue with a policy that can create lifelong change so concerning.

Have there been observational studies in human children on these impacts?

Debiec: Yes. For instance, studies in Romanian children who were raised in orphanages in the 20th century, during a time when the country had no foster family system, have provided knowledge about human growth and development.

Researchers studied the children when they were admitted to the orphanage, when they were adopted out and later in life, including behavioral tests and brain imaging. They found that children's academic accomplishments and overall functioning were affected. They also found that those who were adopted under age 2 or so had some chance of reversing the effects of the trauma of separation, but that those who were adopted later had irreversible changes in their brain images.

This provided key evidence that the early post-birth development matters and that changes can be irreversible.

Why is it important to study separation in animals as well as humans?

Debiec: With animals, mainly rodents, we can do something that we could never do in humans: change the early life adversities they face and see what effects it has on brain development, behavior and more.

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Animal models are much simpler than people, but many functions like threat response and stress response are evolutionarily preserved, so that they're similar across species. In animals, we can look at the molecular level to see changes at a level that we cannot do in humans. We can also look at protective and preventive factors.

For instance, for separation experiments, researchers typically take rodent pups from their mothers for three hours a day for a few consecutive days, though they make sure they otherwise have everything they need. We find changes in the maturation of brain structures and changes in behavior as the pups grow.

Other studies have looked at what happens when juvenile primates are isolated and found long-lasting changes when the separation happens at this stage.

There are many things you can learn from animal models that can be applied to humans or refine our thinking about human trauma. For instance, the discovery of changes in threat processing in animals led to studies in children of the same effect. And studies of biomarkers, such as the level of stress hormones in the blood, in animals have led to explorations of their role in children's response to stress and separation.

Why is early life interaction with parents and others so important?

Debiec: In both rodents and primates, including humans, the young are not born with all the functions they'll need for life — they need to develop them through interactions with others. And if they're deprived of that, they may never develop properly.

In human children, this can include everything from speech to social functions such as how to trust others or behave in a group. All the little behaviors that make us who we are as a social species must be acquired, and to do so we need secure attachments to those around us.

Research in both humans and animals has shown us the importance of attachment cues — the ways of recognizing a caretaker such as a parent by sight, by voice, by smell or touch. These are safety cues, and when an animal or child has those cues around they feel safe.

Can a parent's presence help a child during trauma or upheaval?

Debiec: Yes. We know that the younger the child is during a traumatic time, the more important the emotional state of the parent is, compared with the world outside the child. If the parent is there and is calm and loving, the outside chaos doesn't matter as much. But if the parent is not present or not functional, then that can make the effect of the trauma worse. Even if a parent is not there, support from other relatives or familiar caretakers — the child's social network — may buffer the parent's absence.

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As we develop, we need this one figure that we can attach to for help, and if that isn't there, the feeling of safety and security is undermined. In both human children and young animals, we can see the effects of this in anxietylike behaviors.

What do we know about what's happening in the brains of animals and children who have been separated from parents?

Debiec: In the children raised in orphanages, for instance, their brain's threat-processing structures in the amygdala region of the brain mature much faster than normal — and we see the same in rodents. They become independent in their response to a perceived or real threat and can't distinguish ambiguous situations. They may interpret situations as threatening when they are not, and their responses in stressful situations may be exaggerated.

The developing brain is very adaptable by nature, so when the environment changes early in life, the adaptations become long-lasting. And we can see changes on the microscopic level, in the expression of glucocorticoid receptors on neurons, or systems that process stress in the brain. We can even see epigenetic changes — changes to the way DNA is marked — from chronic exposure to stress hormones.

Can these changes lead to diagnosable mental health issues later?

Debiec: Yes. Early trauma and separation of the kind we're seeing today may "program" a child for life, increasing their risk of depression, anxiety and psychotic disorders. Not only is the cost to the individual potentially very high, so is the potential cost to society.

How does the current situation at the border differ from other losses and traumas a child might experience, such as the death or incarceration of a parent, or placement in foster care?

Debiec: In all those situations, there is still one-to-one support for the child. In the case of a sudden death of a parent, for instance, the remaining family is still there to make the rest of the child's life predictable; not everything changes at once, and there are still familiar adults around. The bond with the child may not be as strong as the bond with the deceased parent was, but the bonds can still buffer the impact.

The same is true for children with incarcerated parents, though there is often the ability to have contact with the parent through visitations or calls.

Children at the border have been rapidly separated from a parent who is likely very frightened. This potentially increases the child's distress.

My colleague Katherine Rosenblum has done extensive work studying children of military parents who are deployed. She and her colleagues have also found that the care provided by the nondeployed parent, contact with the deployed parent by phone or other means, and the continuity of school and activities are important to the children.

With children placed in foster care, there is often an attempt to keep siblings together, which can be great support to the children. And of course, the foster family is there to provide care. But children who go back and forth between their biological family and foster care, or are placed in multiple foster homes, can develop disruptive behaviors, form insecure attachments and lack of trust, or develop a tendency to attach in similar ways to strangers and familiar people.

Orphanages, group homes and the situations we're seeing on the border — situations where children have no connection to familiar adults or even siblings, are not in their usual environment, do not receive one-to-one care and may not even speak the same language as the caregivers — are very different.

Are some children or animals more resilient to the effects of trauma than others?

Debiec: The long-term effects of early life trauma do differ from person to person, but what we see in research and in clinical practice is that having a secure attachment to someone has a protective factor, as does stability of the environment while the brain is developing. Something or someone that is familiar and known, even the ability to hear just the voice of the parent, makes a difference. So does predictability of the surroundings — unpredictability increases stress.

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The type of trauma, how long it lasts, how old the child or animal was when it occurred and genetic factors such as a family history of psychiatric disorders can all change the long-term vulnerability.

Our brains continue to mature until we're in our mid-20s, and so all the functions they control develop until that time, too. We still have much to learn about the interactions of genetic factors and environmental factors in triggering or buffering the impacts of trauma.

What makes humans different from most other species is that we can attach throughout life. So as long as you have positive figures around you, then the trauma may be buffered.

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