This finding could help to identify the regions of the brain where depression symptoms such as negative memories and reduced happiness or pleasure originate.
The new approach, called effective connectivity, "goes beyond the limitations of previous" brain imaging research; it has enabled the team to show how, rather than if, the activity of many different brain areas is related.
Profs. Edmund Rolls and Jianfeng Feng and Dr. Wei Cheng — from the University of Warwick's Department of Computer Science — carried out a study using effective connectivity to measure the influence of one area of the brain on another.
Their new findings were published in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.
"The new method allows the effect of one brain region on another to be measured in depression, in order to discover more about which brain systems make causal contributions to depression," says Prof. Rolls.
Depression causes persistent feelings of sadness as well as loss of interest. The disorder has a significant adverse effect on feelings, thoughts, and behavior and results in a variety of physical and emotional problems.
Source of sadness in depression pinpointed
Prof. Rolls and his team compared 336 people with major depressive disorder with 350 healthy individuals.
Among those with depression, the researchers found that brain regions involved in reward and subjective pleasure received decreased effective connectivity, which may be the source of the decreased happiness that accompanies the disorder.
The brain areas "involved in punishment and responses when a reward is not received" also saw reduced effective connectivity and "increased activity," which could pinpoint the root of sadness in depression.
Brain regions related to memory received increased connectivity and activity, which may explain the "heightened memory processing" and recurring recall of unsettling memories in depression.
"These findings are part of a concerted approach to better understand the brain mechanisms related to depression, and thereby to lead to new ways of understanding and treating depression."
Prof. Edmund Rolls
Dr. Cameron Carter, the editor of Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, adds, "This represents an exciting new methodological advance in the development of diagnostic biomarkers and the identification of critical brain circuitry for targeted interventions for major depression."