People with mental disorders get the short end of the stick. There are still, in 2015, plenty of people dubious of whether mental disorders exist at all. Depressed? Stop being so sad! Bipolar? Just, like, chill out man. Now, an extensive study from researchers at the University of Michigan finds one more piece of tangible evidence to silence doubters: The unfocused, “fuzzy” thinking experienced by some depression and bipolar patients is indeed real, and is caused by observable activity in the brain.
Additionally, the findings support the concept of these conditions (and others, like anxiety) existing on a spectrum rather than as distinct, monolithic illnesses.
“These findings support the idea of seeing mood disorders dimensionally, as a continuum of function to dysfunction across illnesses that are more alike than distinct,” says Kelly Ryan, Ph.D., a U-M neuropsychologist and lead author of the study. “Traditionally in psychiatry we look at a specific diagnosis, or category. But the neurobiology is not categorical — we’re not finding huge differences between what clinicians see as categories of disease. This raises questions about traditional diagnoses.”
The study was large, involving tests given to 612 women, more than two-thirds of which had been diagnosed with either depression or bipolar disorder. They also included data from brain scans of 52 women, who took tests while the scans were administered. The tests required participants to react quickly when specific letters flashed on a screen as part of a rapid, continuing sequence of letters. The study focused on women in order to remove any possible gender differences from the equation.
As a group, women with either form of mental disorder performed worse on the tests than those without, to a noticeable degree. While it’s true that some women in the disordered group performed just as well as healthy women, the bottom 5% of performers all had either depression or bipolar disorder. When performing brain scans on the 52 women, they noticed that those with mental health issues differed from healthy individuals in one key area of the brain. What was surprising that the discrepancies varied based on the disorder.
The right posterior parietal cortex is charged with so-called “executive function,” otherwise known as things like problem solving and reasoning. In both sets of women with mental disorders, activity in this area differed from the control group, but in different ways: Depressed women showed higher than normal activity in the right posterior parietal cortex, while bipolar women showed less. The fact that they affect the same area in different ways leads researchers to believe they may be separate heads of the same hydra, to some degree.
“In all, we show a shared cognitive dysfunction in women with mood disorders, which were pronounced in the cognitive control tests and more nuanced in scans,” says Ryan.
According to Ryan, this idea of mental disorders existing on a continuum is gaining popularity, though they do not advocate for using brain scans to diagnose a disorder, or estimate risk. Far more research needs to be done in order to ethically approve of something like that.