In a new UK study, researchers used a unique approach to investigate the brain activity of patients with major depressive disorder (MDD). They analyzed brain images to better understand how one region of the brain may affect another region, a process known as effective connectivity, in those with MDD.
The imaging approach goes beyond the limitations of previous brain imaging studies, which show if but not how activity of different brain regions are related.
The findings, published in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, reveal that MDD patients show differences in the activity and connectivity of brain systems associated with punishment, reward and memory. The research offers new clues as to which regions of the brain could be at the root of depressive symptoms such as reduced happiness and pleasure.
“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,” said Professor Edmund Rolls at the University of Warwick in the UK.
Rolls conducted the study with Professor Jianfeng Feng and Dr. Wei Cheng.
For the study, the researchers compared 336 people with major depressive disorder to 350 healthy controls. They found that in patients with MDD, brain regions involved in reward and subjective pleasure received less drive (or reduced effective connectivity), which may contribute to the decreased feeling of happiness in depression.
In addition, brain regions associated with punishment and the response of not getting a reward showed increased activity but also decreased effective connectivity, providing evidence for the source of sadness that occurs in the disorder.
Furthermore, the researchers found an increase in activity in the memory-related areas of the brain in MDD patients. The researchers suggest this may be related to heightened memory processing, possibly of unpleasant 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,” said Rolls.
Major depressive disorder, also known as clinical depression, is characterized by a persistently depressed mood and loss of interest in activities. Research suggests that it is caused by a combination of genetic, biological, environmental, and psychological factors.
“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,” said Dr. Cameron Carter, editor of Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.