The finding may help explain why mistreated kids often experience lasting mental problems like depression and other psychiatric disorders.
The study is a counterpoint to recent research that found that children who were nurtured early in life were more likely to have larger brain centers for memory and emotion.
“Stress has a negative impact on brain development; support has a positive impact,” says Joan Luby, MD, a child psychiatrist at Washington University in St. Louis, Mo. Luby studies early emotional development, but she was not involved in the research.
The impact on brain development caused by child abuse may have lasting consequences.
“Having adverse life experiences clearly puts people at risk for mental disorders,” she says.
Tracking the Effects of Child Abuse on the Brain
For the study, researchers recruited almost 200 young adults in the Boston area who were not taking medications and who were not addicted to drugs or alcohol.
Researchers conducted interviews to find out if people had been physically, emotionally, or sexually abused as children. They were also asked about neglect, verbal abuse, or significant separations or losses that may have stemmed from events like death or divorce.
About half of study subjects reported no history of mistreatment. Among those who had memories of abuse, physical or verbal abuse by a parent was the most common kind.
Although verbal abuse may not sound severe, researcher Martin H. Teicher, MD, PhD, a psychiatrist at McLean Hospital in Belmont, Mass., says that in previous studies, he’s seen that verbal abuse can be severely damaging.
“You have to be careful in terms of ridiculing and humiliating children,” he says. “Parental verbal abuse is a severe stressor that’s comparable in magnitude to sexual abuse or witnessing domestic violence.”
About 16% of people in the study reported three or more forms of maltreatment, exposing them to significant levels of abuse.
This group also reported higher-than-average rates of mental illness. Depression was about twice as common and post-traumatic stress disorder (PTSD) was about three times as common in young adults who were significantly mistreated, compared to those who were not.
Next, researchers used magnetic resonance imaging (MRI) scans to measure a part of the brain called the hippocampus.
Why Early-Life Stress Sometimes Leads to Mental Illness
Previous studies have linked the hippocampus to a host of activities. It is thought to be important for forming, sorting, and storing new memories and for processing emotions. But the hippocampus is also vulnerable to stress. Studies have found that people and animals exposed to stress hormones over a long period of time have smaller hippocampi than those who are not similarly stressed.
Shrinkage in this brain region has been shown in people who have mental illnesses like schizophrenia and depression.
Researchers found that three key regions of the hippocampus were nearly 6% to 7% smaller in people who were significantly mistreated as kids compared to those who were not.
The brain findings were there, whether or not a person was showing signs of a mental illness like depression or PTSD.
Based on previous research, “It seems like there’s this sensitive period between 3 to 5 years of age when the hippocampus may be very sensitive,” Teicher says.
“The consequences may not be [apparent] initially; they may be silent for many years before they unfold,” he says.
But he says people who had rough childhoods should also know that although early life experiences may be important for brain function, other studies have shown that some of the brain changes can be undone.
“Things like vigorous exercise will change it. Mental stimulation will influence it,” Teicher says. “Changes in the hippocampus are plastic and can be modified.”