Dr. Joan L. Luby, professor of child psychiatry at Washington University School of Medicine in St. Louis, and colleagues said the brain-imaging study involved children ages 7-10 who had participated in an earlier study of preschool depression that Luby began about 10 years ago.
The earlier study involved children ages 3-6 who had symptoms of psychiatric disorders including depression, or were mentally healthy with no known psychiatric problems.
In the initial study, the children were closely observed and videotaped interacting with a parent, almost always a mother, as the parent was completing a required task, and as the child was asked to wait to open an attractive gift. How much or how little the parent was able to support and nurture the child in this stressful circumstance -- designed to approximate the stresses of daily parenting -- was evaluated by raters who knew nothing about the child's health or the parent's temperament.
"It's very objective," Luby said in a statement. "Whether a parent was considered a nurturer was not based on that parent's own self-assessment."
For the current study, the researchers conducted brain scans on 92 of the children who had had symptoms of depression or were mentally healthy when they were studied as preschoolers.
The study, published online in the Proceedings of the National Academy of Sciences Early Edition, found imaging revealed children without depression who had been nurtured had a hippocampus almost 10 percent larger than children whose mothers were not as nurturing.
A larger hippocampus is a key structure of the brain important to learning, memory and response to stress, Luby said.