Nicholas Thomas remembers a coat rack. "We were at a family gathering," Thomas said. "I think it was Christmas or something, and we were playing hide-and-go-seek. I knocked over a coat rack and I felt like I had done something terribly wrong." That was when he was 12. Thomas, who was diagnosed with depression at 22 years old, said that he finds himself continually reminding himself of everything that he thought he'd done wrong over the years. "I'd hear a little voice in my head berating me," Thomas said.

Some scientists now believe that extreme feelings of guilt in children, such as the ones Thomas felt, can be a strong warning sign for mental disorders such as depression, anxiety, obsessive compulsive disorder (OCD), and bipolar disorder later on in life. Research has long linked excessive feelings of guilt to mental disorders in adults—the DSM-V lists feelings of excessive guilt as a symptom for depression. But researchers at Washington University in St. Louis have found that excessive guilt in children might be linked to a part of the brain that is connected to controls for several different mental disorders.

As a part of a 12-year study, the researchers looked at a part of the brain called the anterior insula, which regulates perception, self-awareness, and emotion. Smaller anterior insulas have been linked to anxiety disorders, depression, schizophrenia, and other mood disorders.

The researchers took brain scans of 145 school-aged children. They also asked the caregivers to identify whether their kids had exhibited any symptoms of excessive guilt, such as apologizing constantly for minor misbehavior or feeling guilty about things that had happened a long time ago. The researchers found that feelings of extreme guilt correlated highly with smaller anterior insulas.

"In the kids who had high levels of guilt, even the kids who weren't necessarily depressed, they had smaller anterior insula volume, and that smaller anterior insula volume is predictive of later occurrence of depression," said Joan Luby, one of the study authors. "This research suggests that early childhood experiences impact the way the brain develops."

Luby says that findings, which were published in JAMA Psychiatry in November, are significant because it is one of the first studies that links feelings of excessive guilt in children to physical differences in the brain. "There have been a lot of behavioral studies done with children," Luby said. "In terms of brain changes in children ... there's very little data on that."

Michelle New, a psychologist and associate professor at the George Washington University Medical School in Washington, D.C., said that this research could help pinpoint specific brain anatomy to identify children who are at high risk for later-life mental disorders. "This research is really new and exciting because you can look at changes in the brain, and it shows that early intervention is really important. Dismissing early symptomatology is dangerous," she said. New explained that mental disorders are often latent between the ages of four and 12, and so being able to identify children at high risk for mood disorders helps parents and mental-health professionals engage in preventative measures earlier in life.

In addition, this research provides neurological evidence for what researchers have been starting to suspect: Guilt in early childhood has negative effects on children and may cause later life depression and anxiety. In a study published in 2013 by scientists at the University of Jyväskylä, Finland, researchers found that parenting tactics that created feelings of guilt in children caused children to feel an increase in distress and anger for many days afterward. In another study published in 2003, scientists found that children whose parents used guilt-inducing tactics were far more likely to internalize their problems. Depression and anxiety are classic examples of internalizing disorders.

The question is whether guilt causes later life mental disorders or if a biological predisposition to mental disorders causes early symptoms of excessive guilt. But New says that doesn't matter in the clinical setting.

"It's not like that symptom is going to go away," she said. "What's important is that we practice early intervention and prevention."

The researchers at Washington University are also looking at effective ways to help children manage guilt, in case that could mitigate later life mental disorders. Luby says that they are in the early stages of looking at how psychotherapy affects child behavior and how it affects brain function. "We are still in the first year, but my clinical impression is that these kids are getting a lot better," Luby said.