Identifying the first reliable biomarker for depression
While there are currently biomarkers that have been identified for depression, they are not generally reliable and have, so far, not been widely applied in clinical use. Now, researchers have identified what could be the first reliable biomarker for the condition – potentially transforming its diagnosis and treatment.
The brain uses networks to coordinate its activity – such as the Default Mode Network which co-ordinates mental processes, and the Frontoparietal Network which coordinates attention and executive function, among others.
One network, the Salience Network coordinates attention allocation, reward processing and switching between different brain networks – playing a crucial role in regulating the switch between the Default Mode Network and the Frontoparietal Network.
In this commentary examining recent research findings from a study published in Nature, the researchers suggest that the Salience Network appears to be functionally twice as large in people with depression as in those without the condition.
The commentary has been published in Genomic Psychiatry and carried out by researchers at the University of Ottawa and the University of California San Francisco.
“What makes this discovery so significant is that the expanded salience network predates the onset of depressive symptoms and remains stable regardless of symptom severity or treatment interventions,” explained Dr. Nicholas Fabiano, co-author of the commentary from the University of Ottawa’s Department of Psychiatry.
“We’re potentially looking at a distinctive neural signature that could identify individuals at risk for depression before they experience symptoms.”
A new biomarker for depression?
The researchers say that this characteristic brain connectivity pattern was observed consistently across individuals with depression, suggesting its potential as a depression biomarker.
“By identifying those at risk before they experience the full impact of depression, we can intervene earlier, leading to lasting improvements in their quality of life,” said Katerina Palacek from the University of Ottawa’s Faculty of Medicine.
The team say that enabling this early identification could decrease the chances of relapse, shorter periods of remission, and longer depressive episodes, and propose three potential mechanisms underlying salience network expansion.
Firstly, they suggest that the enlarged network could represent a compensatory response based on increased usage of this network in individuals predisposed to depression.
Secondly, they suggest there may be genetic factors contributing to the development of an enlarged salience network in those who later develop depression.
And thirdly, the team suggest that the salience network might appear relatively enlarged as a consequence of atrophy in other brain regions that could predate depressive symptoms.
“While we observe similarities between regions implicated in depression-related brain atrophy and the salience network, including the insular cortex and anterior cingulate cortex, there are also notable differences,” said Dr. Robin Carhart-Harris, co-author from the University of California San Francisco’s Weill Institute for Neurosciences.
“This suggests complex interactions between various brain networks in depression that we’re just beginning to understand.”
Depression as a neural connectivity disorder
A theory behind the cause of depression that has been influential over recent decades is the chemical imbalance theory – suggesting that depression is caused by neurotransmitter imbalances.
However, more recent research has led to criticism of this theory – leaning towards an understanding of the condition being influenced by a variety of complex factors.
The researchers say that these findings on the Salience Network highlight the need to reconceptualise depression as a disorder of neural connectivity, which could have implications for developing targeted therapeutic approaches.
“Depression is not a simple disease characterised by independently functioning brain areas or isolated neurotransmitter imbalances,” said the researchers.
“By record, it is a multifaceted condition with altered brain-wide connectivity that cannot be comprehensively understood through fragmented lenses.”
The researchers say that the new findings highlight the value in investigating how established treatments, such as antidepressants, exercise, diet modifications, and novel depression treatments, such as electroconvulsive therapy, ketamine, and psychedelics, might impact the salience network’s functional connectivity – suggesting longitudinal studies are carried out to establish how the size of the salience network evolves with different treatment modalities.
