Mental illness: MRI reveals white matter clues

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  • Published: Oct 1, 2016
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: Mental illness: MRI reveals white matter clues

What's the matter?

In the 37 studies the researchers looked at, participants with emotional disorders had less directed water movement in their white matter compared to participants who did not have emotional disorders.

Emotional disorders, such as depression and anxiety have a lot of symptoms in common and scientists have long suspected that related problems in the brain might give rise to these disorders, which commonly involve persistent "negative" emotional states and thoughts. Moreover, similar treatments seem to have positive effects in different conditions. Now, a combined analysis of MRI scans of the brain's white matter confirms that various mental illnesses may have connected underlying elements.

Lisanne Jenkins, Scott Langenecker, Alyssa Barba, Miranda Campbell, Melissa Lamar, Stewart Shankman, Alex Leow, and Olusola Ajilore of the University of Illinois at Chicago publish details in the journal NeuroImage: Clinical of their analysis of existing MRI images that reveal common brain abnormalities found in multiple emotional disorders. "This study provides important insights into mechanisms shared across multiple emotional disorders, explains Langenecker, "and could provide us with biomarkers that can be used to more rapidly diagnose these disorders." He told SpectroscopyNOW that, "By understanding and acknowledging what is shared, we can better move on to what is unique and may require specific treatments." Sometimes mental illness persists without an accurate diagnosis for many years leading to chronic problems for countless patients that might otherwise have received treatment and had better outcomes for their condition in the long term.

The team's work involved a systematic trawl of the scientific literature in order to net research papers in which whole-brain "diffusion tensor" imaging on adults with major depressive disorder, bipolar disorder, social anxiety disorder, obsessive-compulsive disorder, or post-traumatic stress disorder, had been undertaken. Diffusion tensor imaging, or DTI, measures the degree to which water molecules move in one direction rather than randomly diffusing in all directions. It provides, what the team describes as an indirect measurement of the microstructure of white matter, and can give information about connectivity of different parts of the brain.

Superior view

The team also hauled in MRI scans from otherwise healthy control subjects. They caught thirty seven studies that met the requisite criteria and represented scans of almost one thousand people (962 participants to be precise) with emotional disorders and 892 healthy control subjects. A meta-analysis of the data was then carried out to see whether white-matter alterations were present in those people with multiple mood disorders and which might be unique to a particular mood disorder.

Langenecker’s group identified a common difference in the white matter, structure of the brain in patients with emotional disorders that was not present in those without these brain illnesses. The difference was manifest as disruption in a region of the brain that connects different parts of the so-called "default-mode network". In the 37 studies the researchers looked at, participants with emotional disorders had less directed water movement in their white matter compared to participants who did not have emotional disorders. The default-mode network part of the brain is known to be responsible for passive thoughts that are not focused on a particular task. The region is the left superior longitudinal fasciculus, the SLF. This same structure also connects the default-mode network and the cognitive control network, which is important in task-based thinking and planning. The two regions tend to function alternately with each other. Langenecker points out that a hyperactive default-mode network closely correlates with patients who have constant negative thoughts or ruminations associated with most emotional disorders.

Reining it in

"If the part of the brain that helps rein in the default-mode network isn't as well-connected through the SLF, this could explain why people with emotional disorders have such a hard time modulating or gaining control of their negative thoughts," Langenecker adds. One of the more surprising observations was that people with OCD shared the most brain abnormalities with people with other emotional disorders. "We would have expected OCD to look very different from other emotional disorders, because the symptoms are so unique and distinct," Langenecker suggests. "But this kind of flips how we see OCD, which clearly has more in common with other emotional disorders than we think."

Conventional medical wisdom describes OCD as being associated with repetitive thoughts about specific objects or tasks, externalised thoughts. By contrast, depression, social anxiety, and panic disorder are associated with internalised emotions, thoughts directed at the self. "Our finding that OCD is more like the other emotional disorders makes sense," says Ajilore. "We may now be able to further examine commonalities between these disorders that could improve our treatment of them individually."

The one mental illness that was prominent as not having the most number of distinct white matter disruptions apart from the others was post-traumatic stress disorder (PTSD), a condition triggered, as the name would suggest, by traumatic events. People with PTSD had several areas of low white-matter connectivity that were not seen in the other emotional disorders. Milder forms of trauma can be present in the patient history in major depression or generalized anxiety, but the distinct brain regions affected in PTSD are more definitively associated with severe and often repetitive trauma.

Related Links

NeuroImage: Clin 2016, online: "Shared white matter alterations across emotional disorders: A voxel-based meta-analysis of fractional anisotropy"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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