A recent study published in Nature by researchers from Weill Cornell Medicine has revealed that individuals with depression have a brain network nearly twice as large as those without the disorder.
The Salience Network
This network, known as the frontostriatal salience network, comprises regions in the frontal cortex and the striatum. It plays a crucial role in processing rewards and detecting salient or significant stimuli in the environment. The salience network helps the brain decide what information is important and should capture our attention. Graphic from Schimmelpfennig and colleagues (2023).
Depression is a mental health condition affecting about five percent of adults worldwide. Episodes of low mood, loss of interest or pleasure in activities, poor concentration, and feelings of low self-worth characterize it. Notably, depression is episodic, meaning individuals experience periods of depression interspersed with periods of wellness. This episodic nature has often made it challenging for researchers to identify consistent structural differences in the brains of those with depression compared to healthy individuals.
In this groundbreaking study, over 140 people diagnosed with major depressive disorder and 37 healthy controls underwent multiple brain scans using functional magnetic resonance imaging (fMRI) over 1.5 years, with some participants scanned up to 62 times. The researchers employed precision functional mapping (PFM), which involves collecting a large volume of fMRI data over time to estimate brain function metrics for individuals. This approach allowed for a more detailed and personalized assessment of brain structure and connectivity.
The findings were striking: the frontostriatal salience network was nearly two times larger in participants with depression compared to healthy controls. This expansion was stable over time and did not fluctuate with the individual's mood state. While the size of the network remained constant, the activity within it did vary depending on whether the person was experiencing a depressive episode. Decreased activity within the salience network was observed in participants who were actively depressed. Moreover, this reduced activity could predict whether an individual would have a depressive episode in the following week.
The researchers expanded their analysis to include data from hundreds of other patients scanned less frequently to broaden their understanding. They discovered that the enlarged salience network was also present in children as young as nine years old who had no prior history of depression but later developed the condition during adolescence. This suggests that some individuals may be pre-wired to develop depression due to inherent differences in their brain networks.
The implications of this study are significant. The enlarged frontostriatal salience network could serve as a potential biomarker for identifying individuals at risk of developing depression. Early identification could lead to timely interventions, potentially mitigating the severity or even preventing the onset of depressive episodes. Additionally, understanding the role of the salience network in depression opens new avenues for exploring how different treatments might affect brain network activity. The researchers also plan to investigate whether similar patterns of network expansion are present in other mental health conditions that share symptoms with depression, such as bipolar disorder and obsessive-compulsive disorder.
Summary
The study sheds light on a fundamental difference in brain structure associated with depression, emphasizing the role of the salience network in the disorder. The salience network's normal function is to help the brain prioritize important stimuli and process rewards, but its enlargement in depressed individuals may increase the risk of developing depression. This discovery not only enhances our understanding of the neural underpinnings of depression but also holds promise for improving diagnosis and treatment strategies.
Glossary
frontostriatal salience network: a neural network connecting the brain's frontal cortex and striatum regions. It is crucial for detecting and filtering important stimuli, helping the brain prioritize significant information over irrelevant data. Alterations in this network have been associated with mental health conditions like depression, where it may be enlarged, and exhibit decreased activity during depressive episodes.
functional magnetic resonance imaging (fMRI): a non-invasive imaging technique that measures and maps brain activity by detecting changes associated with blood flow. When a brain area is more active, it consumes more oxygen, and fMRI can capture these changes in blood oxygenation levels. This allows researchers to observe brain functions, connectivity, and responses to tasks or stimuli in real time.
major depressive disorder (MDD): a mental health condition characterized by persistent feelings of sadness, loss of interest or pleasure in activities, changes in appetite or sleep patterns, fatigue, poor concentration, and feelings of worthlessness or guilt. MDD is episodic, with periods of depression alternating with periods of wellness, and affects about five percent of adults worldwide.
precision functional mapping (PFM): an advanced neuroimaging approach that involves collecting a large volume of fMRI data from the same individual over time. PFM provides detailed and personalized assessments of brain structure and connectivity by creating high-resolution maps of an individual's brain activity patterns. This method enhances the ability to detect subtle neural differences and changes, improving the understanding of brain function and disorders.
Open-Source References
Lynch, C. J., Elbau, I. G., Ng, T., Ayaz, A., Zhu, S., Wolk, D., Manfredi, N., Johnson, M., Chang, M., Chou, J., Summerville, I., Ho, C., Lueckel, M., Bukhari, H., Buchanan, D., Victoria, L. W., Solomonov, N., Goldwaser, E., Moia, S., Caballero-Gaudes, C., … Liston, C. (2024). Frontostriatal salience network expansion in individuals in depression. Nature, 633(8030), 624–633. https://doi.org/10.1038/s41586-024-07805-2
Schimmelpfennig, J., Topczewski, J., Zajkowski, W., & Jankowiak-Siuda, K. (2023). The role of the salience network in cognitive and affective deficits. Frontiers in Human Neuroscience, 17, 1133367. https://doi.org/10.3389/fnhum.2023.1133367
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