People with major depressive disorder (MDD) have abnormal connectivity between several key regions of the brain responsible for emotional behavior, learning, memory and decision-making, says a new study.
MDD is a severely debilitating illness characterized by sadness and an inability to cope.
Not only does it affect a person's ability to concentrate and make decisions, it also alters their ability to experience pleasurable emotion, and instead prolongs negative thoughts and feelings.
The new research from Stanford University used functional magnetic resonance imaging (fMRI) to show aberrant connectivity in depressed brains.
The researchers compared the fMRI scans of women. Half of the women were diagnosed with depression at the time of the scan and the other group consisted of women who did not currently have, nor had ever had, severe depression.
fMRI measures changes in blood flow and by overlaying images of depressed and unaffected brains, a number of differences came to light.
The images showed that the depressed had decreased connectivity between several key regions of the brain responsible for emotional behaviour, learning, memory and decision-making.
"In addition to decreased connectivity between emotion processing regions of the brain, we found that depression was linked to an increase in connectivity between the dorsal caudate and an area of the prefrontal cortex," explained one of the researchers, Daniella Furman.
"Deep within the brain, the caudate is thought to be involved in learning, motivation, and emotion while the prefrontal cortex at the front of the head is involved in maintaining goals and likely regulating emotional behaviour. Together, these regions may act to filter out irrelevant thoughts or actions.
"Greater connectivity between the dorsal caudate and prefrontal cortex might reflect the inability of the depressed to update their working memory and, as a result, sustains negative thoughts. In fact we found evidence for a parallel increase in tendency to ruminate on bad thoughts," she added.
The study has been published in BioMed Central's open access journal Biology of Mood and Anxiety Disorders.