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.
The King’s College researchers used a dataset that included clinical, genetic, and, neuroimaging data of 682 youth from France, Germany, Ireland, and the United Kingdom collected as part of a European research project known as the IMAGEN Study — one of the first longitudinal studies to research adolescent brain development and mental health. In longitudinal studies, data is collected over a number of years. This allows researchers to track kids over time and determine whether certain experiences — such as being bullied — are associated with structural changes in the brain. The youth completed questionnaires at ages 14, 16, and 19 on the extent of bullying in their daily lives. MRI scans were acquired at ages 14 and 19. The researchers identified nine regions (left and right) of interest that are associated with stress and maltreatment.
Analyzing changes in brain volume at age 19, they found that participants who experienced chronic bullying had significantly steeper decreases in the volume of two regions involved in movement and learning — the left putamen and left caudate — with the former showing the stronger effect. These participants also experienced higher levels of generalized anxiety.
“The relationship between peer victimization and generalized anxiety was due at least in part to these steeper decreases in volume,” says Erin Burke Quinlan, a neuroscientist at King’s College London and the paper’s lead author. She says this “suggests — similar to the maltreatment literature — that the areas of the brain are getting almost too small.” An earlier study published in the American Journal of Psychiatry in 2010 also reported abnormalities in certain brain regions that correlated to reported verbal abuse by peers, though the research was not longitudinal and involved participants aged 18 and older. Even though her work shows changes over time, Quinlan notes that “the brain is plastic throughout our life. That’s how we continue to learn, that’s how environment continues to shape our behavior.” So it’s not possible to tell whether the decreased volume depicted on the MRI represents a permanent or temporary state.
Research on the neurobiology of peer victimization is roughly 15 years behind similar research on child maltreatment, says Vaillancourt, a Canada Research Chair in Children’s Mental Health and Violence Prevention at the University of Ottawa. “Just saying maltreated children ‘were sad’ was not enough to get funding” for research and targeted interventions, she says. That change didn’t occur until experts testified before Congress and showed brain scans of children who had been maltreated. Vaillancourt believes the scans provided persuasive evidence that children are measurably impacted by abuse and neglect. The study of chronic bullying, she suggests, could follow a similar path.
Quinlan’s team was not able to determine which biological mechanism altered the brain volume of the youth in their study. Vaillancourt and other researchers suggest that findings from the child maltreatment literature could provide one possible explanation. In these studies, “toxic” stress and the stress hormone cortisol appear to alter brain development.
The body’s stress response is regulated by the hypothalamic pituitary adrenal axis. The hypothalamus — an almond-sized region near the base of the brain — helps regulate vital sensory data such as metabolism, sleep, temperature, hunger, thirst, and, emotions. The hypothalamus is activated by the amygdala — an important region for processing emotions — when danger is detected. Following their initial release of adrenaline, if danger continues to be perceived, the adrenal glands release cortisol into the bloodstream. Higher levels of cortisol allow the body to operate at higher performance when it is exposed to an acute stressor. But chronic stress — such as experiencing persistent bullying — could have just the opposite effect because memory, cognition, sleep, appetite and other functions are continually on “alert” and not allowed to repair.
Cortisol receptors are in most cells throughout the body. The toxic stress of experiencing chronic bullying could lead to damage to receptor sites and the death of neural cells, some researchers believe, and thus the many downstream negative outcomes, such as lower academic achievement and depression.
The literature consistently finds that maltreated and bullied youth typically have low cortisol, says Vaillancourt. “That is very important because we see that blunted cortisol signature with other psychiatric issues that are associated with extreme trauma [such as in] post-traumatic stress disorder, individuals who come back from combat or who have been repeatedly raped, or in concentration camps during the Holocaust,” she says.
The longitudinal data of Quinlan’s team is “fascinating,” says Andrea J. Romero, a social psychologist at the University of Arizona who researches the intersections of gender, race, ethnicity, culture, and psychology. It “doesn’t seem far-fetched and makes sense during the adolescent period because it is a period of critical growth.” It’s interesting, Romero adds, “to think there are direct physiological pathways of social experience that are affecting mental health.”
Romero has collected data on peer victimization as well, including a study on the elevated rates of bullying, depression, and suicide ideation among Latina teens. The psychologist echoes Vaillancourt’s belief that neuroimaging could have a powerful impact on government and policy interventions to address bullying. But additional qualitative research is also needed, she says. For example, this could take the form of a daily diary where young people as early as fourth or fifth grade document their bullying experiences. The results “might be very unique based on intersections of race, class, gender, sexual orientation, and gender expression,” says Romero.
One of the most interesting findings by Quinlan’s team, Vaillancourt adds, were the brain regions that experienced the steepest decreases in volume. “The regions that they are correlating with peer victimization did not seem obvious to me,” she says.
“They’re looking at things that are historically related to motor control, so I was kind or surprised by that,” Vaillancourt adds.
Vaillancourt says that the anterior cingulate cortex (ACC) “or another region implicated in social pain research” may have been a more obvious choice. The ACC is one of the brain regions that processes physical pain. That same neural circuitry is activated when someone experiences the “social pain” of events such as grief, rejection, exclusion, humiliation, or bullying, according to a number of studies over the past decade.
The participants in IMAGEN are largely Caucasian, Western European, and middle class, says Quinlan. The researchers are keen to add socioeconomic and racial diversity to their sample. The team is now working with researchers in China, India, and the United States to share neuroimaging and genetic data of adolescents and young adults.
The next steps in the research, says Quinlan, will be to review data from the latest phase at age 22. The researchers collected a significant amount of brain imaging data in addition to genetic and epigenetic data. Through the end of this year, the team is also planning the fourth follow-up for ages 25 and 26.
“What I theorize was that if I were to image the brains in early adulthood, say age 25, that perhaps by then these processes will continue. So, when they are adults these [brain] regions would be significantly smaller,” says Quinlan. “But that was a limitation in that we don’t yet have that brain data available, but we hope to in the next two to three years.”
Rod McCullom is a science journalist in Chicago. His work has been published by Undark, ABC News, The Atlantic, The Nation, Scientific American, and Nature, among other publications.
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