A team of researchers studying the impact of stress upon children has published new evidence suggesting that there is a “sensitive period” lasting through age 5 in which severe stress appears to have its greatest impact on the hippocampus, a part of the brain known to be stress-sensitive.

Stress severity for events experienced prior to age 6 was correlated in the study with smaller hippocampi, as measured by volume. (Every person has two of these seahorse-shaped structures, one on each side of the brain.) For reasons not yet clear, the team found no correlation between stress severity and hippocampal volume for events experienced between the ages of 6 through 13.

“Our findings have important clinical implications,” say the researchers, explaining that smaller hippocampal volume has been linked in past studies with problems later in life: heightened vulnerability to brain and behavior disorders following trauma; poorer antidepressant response; and memory deficits.

There are a great variety of ways in which stress can be measured and evaluated. While some researchers have focused on its cumulative impact over periods of years, others have explored the impact of its severity.

Kathryn L. Humphreys, Ph.D., a 2015 BBRF Young Investigator at Vanderbilt University, and colleagues, placed their focus on severity, and particularly the timing of severely stressful events in a young child’s life. Their sample consisted of 178 children drawn from a northern California community, aged 9 to 14, part of a larger sample of children being studied from childhood through puberty. 2015 BBRF Young Investigator Sarah J. Ordaz, Ph.D., was also on the team.

Sixty-three percent of the 178 children reported a stressful event prior to age 6. All but three of the 178 reported at least one stressful event later in childhood. The children received brain scans, which enabled the team to measure and compare their hippocampi, correlating the results with each child’s history of stress. Parental reports of stress were also part of the study.

“While our results clearly show differences in hippocampal volume after early-life stress,” the researchers noted, “they should not be taken to indicate that only events early in life are meaningful.” They also cautioned that stress, early in life or later, can affect other parts of the brain; their work is specific to the hippocampus, a region that plays a crucial role in the consolidation of memories, both long- and short-term.

“In the future, it will be important to focus on how to prevent stress in early life and how best to buffer children from the harmful effects of stress,” Dr. Humphreys said.