Adolescents who experienced abuse or neglect as children have fewer brain cells than teens who did not undergo childhood maltreatment, a new Yale study finds.

A study conducted by scientists from the Yale School of Medicine, published in the Dec. 5 edition of Archives of Pediatric Adolescent Medicine, found that adolescents who were exposed to maltreatment as children showed a reduction in gray matter in areas of the brain that control emotions and impulses, though they had not been diagnosed with a psychiatric disorder. It found that the specific brain areas affected may differ according to whether adolescents reported experiencing abuse or neglect, whether the maltreatment was physical or emotional and whether they were male or female. Experts cautioned that the results of the study were only an association, and longer-term studies were needed.

“Though these kids do not have a diagnosable psychiatric disorder, they are still showing physical signs of maltreatment,” said Hilary Blumberg, associate professor of psychiatry in the Child Study Center and the senior author of the study. “The results could explain possible difficulties in school or future depression or behavioral issues.”

Forty-two adolescents filled out questionnaires that measured their perceived exposure to physical and emotional abuse, as well as physical and emotional neglect as children. Structural MRI scans found reductions in the prefrontal cortex, important in emotional and behavioral regulation, across all cases of maltreatment. Other areas affected depended on the type of maltreatment reported.

Those who reported physical or emotional neglect, for example, showed reductions in the cerebellum, which controls motor functions and regulates pleasure and fear. Those who had been exposed to physical abuse in particular showed reductions in the insula, an area that controls self-awareness ­­— which may explain why so many people who have been abused as children report out-of-body experiences, Blumberg said.

The study also found gender differences in the grey matter losses. In girls, the reduction was concentrated in areas important in regulating emotion, while in boys, the reduction was seen in areas important in impulse control. Because depression is associated with an inability to regulate emotions, this finding highlights the fact that the rate of depression is much higher in women than men, according to Jennifer Pfeifer, an assistant professor of psychology at the University of Oregon, who wrote an editorial on, a major science news website, critiquing the study.

Blumberg said that despite the physical symptoms of childhood maltreatment, some adolescents in the study remained more resilient than others. Pfeifer and her colleague Philip Fisher, also of the University of Oregon, speculated two possible reasons for this apparent resilience in their editorial. The structural decreases may have left adolescents vulnerable to future psychological problems — which just haven’t occurred yet, or the adolescents tested have found alternative mechanisms to adapt to their difficult surroundings.

Because it only shows correlation, the study cannot prove that childhood maltreatment precipitated any structural changes in the brain, said Everett Waters, professor of psychology at the State University of New York at Stony Brook.

“It is also possible that brain problems led to the kids being abused,” Waters said, “or more likely, that some third factor led to both the brain problems and the abuse.”

Waters and Pfeifer both emphasized the importance of conducting a longitudinal study that would track children from infancy, in order to better understand the development of structural differences in the brain. Linda Mayes, a co-author of the study, said she will continue to track this group of adolescents and monitor them to see if they develop psychiatric disorders.

The research was funded by the National Institutes of Health.