In recent years, a steadily increasing volume of data has demonstrated that peer victimization - the clinical term for bullying impacts hundreds of millions of children and adolescents, with the effects sometimes lasting years and, possibly, decades. The problem is even recognized as a global health challenge by the World Health Organization and the United Nations. And yet, researchers maintain there is still a limited understanding of how the behavior may physically shape the developing brain.

Bullying is usually defined as repeated and intentional verbal, physical, and anti-social behavior that seeks to intimidate, harm, or marginalize someone perceived as smaller, weaker, or less powerful. Among younger children, common forms of bullying include abusive language and physical harm. This behavior may grow subtler with age as adolescent bullies routinely exclude, insult, and mock their targets. Sometimes this behavior escalates into “mobbing” among groups of bullies in school, work, or cyberspace.

Researchers believe more than 3.2 million American students experience bullying every year. That’s about 1 percent of the nation’s total population. Among these students, about 10 to 15 percent experience “chronic” or persistent bullying that will last more than six continuous months. Experiencing chronic peer victimization is associated with lower academic achievement, higher unemployment rates, depression, anxiety, post-traumatic stress disorder, substance abuse, and self-harm and suicidal thoughts.

Most of the research into the neurobiological processes that might contribute to these negative health outcomes has occurred in the past decade, much of it focused on bullying’s impact on the body’s stress response system. A paper published last December in the journal Molecular Psychiatry sheds some light on a different area: brain architecture. The trauma stemming from chronic bullying can affect the structure of the brain, according to longitudinal magnetic resonance imaging (MRI) data collected by an international team based at King’s College London. The findings echo previous research, which has demonstrated similar changes in children and adults who experienced what’s known as “child maltreatment” neglect or abuse by adult caregivers.

Long-term changes to the brain’s structure and chemistry are an indicator “of how sinister bullying is” says Tracy Vaillancourt, a clinical psychologist at the University of Ottawa. Along with others in the field, she is hopeful that studies like the one from King’s College will be a catalyst for further research which could ultimately be used to inform policy decisions and support anti-bullying interventions.

This article originally appeared on : Time