A key brain structure that regulates emotions tends to be smaller in young adults with greater depressive symptoms, according to a new study published in Psychiatry Research: Neuroimaging. The research examined the relationship between the amygdala, a pair of almond-shaped brain structures, and depressive symptom severity.

“Volumetric differences in several brain regions have been reported in people with depression. The amygdala is interesting because studies have reported smaller, larger and the same average amygdala volume in depressed people as compared to controls,” explained study author E. Sherwood Brown, a professor of psychiatry and director of the Psychoneuroendocrine Research Program at The University of Texas Southwestern Medical Center.

“Since the amygdala is involved in the processing of emotions, such as fear and anxiety, it is possible that depressed people might process more strong emotions which would, in a sense, make the amygdala work harder and increase in size. On the other hand, increases in the stress hormone cortisol in depression might be harmful to the amygdala and make it become smaller. Finally, it is possible that one might just have either a smaller or larger amygdala which alters processing of emotions and make one more vulnerable to depression.”

“All of these possibilities make the amygdala a particularly intriguing brain region to examine in depression. Our objective with this study was to use the very large sample size of the Dallas Heart Study to examine the relationship between current depressive symptom severity and amygdala volume in the overall sample and in subgroups of participants,” Brown said.

For their study, the researchers analyzed MRI brain scans from 1,797 individuals. They found no evidence that depressive symptom severity was associated with amygdala volume overall. But there was one exception: In young adults, greater depressive symptom severity was associated with smaller amygdala volume.

“The relationship between depression and amygdala volume may differ between subgroups of people. Perhaps different demographic characteristics of research participants may, at least in part, explain the disparate findings in prior research studies,” Brown told PsyPost.

“We found a significant negative relationship between depressive symptom severity and amygdala volume in young adults but not in other age groups. Thus the take away may be the depression is a heterogeneous disorder.”

Brown and his colleagues also examined the possible influences of gender, ethnicity, education, BMI, and psychotropic medication use. But none of these factors appeared to moderate the relationship between depressive symptom severity and amygdala volume.

The study — like all research — includes some limitations.

“The study has several limitations that are somewhat inherent in research using large databases. We used a validated depressive symptom severity scale. However, we did not have information about the length of time the participants might have been depressed or even a clinical depression diagnosis. It would have been useful to have had more information about their symptoms,” Brown explained.

“A question yet to be answered is why young adults might show a relationship between depressive symptom severity and amygdala volume. The finding could reflect differences in the nature of depression throughout the lifecycle. However, the current study was not able to answer this question.”

Brown added that depression is associated with several physical changes in the brain.

“I feel that it is important to think about depression not just as a mood state, but rather as an illness that can be associated with changes in the brain and other organs. Changes in the amygdala are just one example,” the researcher said.

“Numerous studies and meta-analyses of their data have suggested a reduction in the volume of the hippocampus in depression. Brain volume changes may be biomarkers of depression vulnerability or possibly consequences of depression. Answering these questions might provide insights into the mechanisms underlying depression.”

The study, “Relationship between depressive symptom severity and amygdala volume in a large community-based sample“, was authored by Shivani Daftary, Erin Van Enkevort, Alexandra Kulikova, Michael Legacy, and E. Sherwood Brown.