Investigators Yvette I. Sheline, M.D., and Deanna M. Barch, Ph.D., and a team at Washington University in St. Louis have identified a key difference in the way the brain functions in people who are depressed compared to those who are not.
The study, published in the Feb. 10 issue of the Proceedings of the National Academy of Sciences, demonstrates that brain regions collectively known as the default mode network behave differently in depressed people.
The default network typically is active when the mind wanders. It shuts down when an individual focuses on the job at hand. But the researchers found the network stays active in people who are depressed even when they are concentrating on specific tasks. The new work suggests that individuals with depression may not be able to lose themselves in work, music, exercise or other activities that enable most healthy people to get outside of themselves.
One characteristic of the default network is that it tends to involve self-referential functions. For example, it may involve memories, not just memories of facts or information, but about our own experiences and how they relate to that information — the difference between remembering that hijacked planes crashed into the World Trade Center on Sept. 11 and remembering where you were when you watched or heard about the attack.
Brain regions in the default network assess what is going on inside of us, to survey the effects of the environment around us and to make judgments about whether or not we approve. Scientists have linked the network to inward-looking activities, a kind of internal narrative of our life stories.
The research team used functional magnetic resonance imaging (fMRI) to scan the brains of 20 people with major depression as well as 21 individuals who were not depressed. None of the people in the study were being treated with antidepressant drugs at the time of their brain scans. Once in the scanner, they were shown pictures designed to evoke emotion, from snarling dogs and violent scenes to pictures of flowers and smiling faces.
Sometimes, study subjects simply reacted to the picture as they saw it.