Multimodal neuroimaging has confirmed that major depressive disorder is associated with a deregulation of brain regions.
Experts had surmised that both structural and functional abnormalities were present in major depression although the precise nature of the dysfunction was obscure.
In the new study, Dr. Bart de Kwaasteniet at the Academic Medical Center in Amsterdam found irregularities in the brain’s prefrontal cortex and in the limbic system.
The researchers, led by Professor Damiaan Denys, recruited 18 patients with major depressive disorder and 24 healthy individuals, all of whom underwent multiple neuroimaging scans.
Investigators specifically focused on the structural and functional connectivity between the subgenual anterior cingulate cortex (ACC) and the medial temporal lobe, two regions that are connected by a white matter tract called the uncinate fasciculus.
These regions are known to be involved in the regulation of emotion and memory.
These results suggest that structural disturbances in a region called the uncinate fasciculus contribute to abnormally high functional interactions among brain circuits associated with the symptoms of depression.
“This leads to the hypothesis that abnormalities in brain structure lead to differences in connectivity between brain areas in depressive disorder,” added de Kwaasteniet.
However, they also hypothesized that the reverse may be true as well. In other words, that the increased functional connectivity among these brain regions leads to structural changes in the brain’s white matter fibers because of abnormally increased signal transduction.
This hypothesis is supported by recent studies in schizophrenia which suggest that circuit hyperactivity may be a predictor of subsequent cortical atrophy.
“This interesting study suggests that abnormalities in the structural connections between brain regions, the white matter, are associated with abnormal activity within a brain circuit implicated in the symptoms of depression,” commented Dr. John Krystal, editor of Biological Psychiatry, where the study was published.
This observation raises an important question about the implications of treating the circuit functional abnormalities without fixing the underlying brain structure. Perhaps the structural abnormalities contribute to the risk for the relapse of depression among individuals whose brain circuit activity has responded to antidepressant medications.”