People diagnosed with depression or bipolar disorder commonly report that their thinking ability has become less sharp or gotten fuzzy compared to before their symptoms first started. Now, researchers have found that the effect is real, adding to the growing body of evidences that depression and bipolar disorders are part of a mood disorder spectrum.
In a study published in the journal BRAIN, researchers detailed tests given to 612 women, over two-thirds of which have been diagnosed with either depression or bipolar disorder. Subjects were limited to women to take away gender differences that may complicate results. As the study was large for one on mental health, its results have more weight.
Researchers had the subjects quickly react when specific letters were briefly shown on a screen. It was a test that called for sustained concentration as the women were asked to react to a certain letter mixed in with others. Compared to women without mental health problems, those who were diagnosed with either depression or bipolar disorder were noticeably slower.
Some of the women were also subjected to brain scans, results of which showed that women who were depressed or bipolar have different activity levels in their right posterior parietal cortices compared to those who had healthy mental health. This part of the brain affects executive functions, like reasoning, working memory and problem solving.
"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," said Kelly Ryan, Ph.D., lead author for the study.
She adds that in psychiatry, specific categories or diagnoses are present but the same cannot be said for neurobiology. Huge differences were not found between what experts consider as disease categories and this raises concerns regarding traditional diagnoses.
The researchers hope the results of their study can help other researchers looking for ways to split up participants in future research, used as an "intermediate phenotype" for mood disorders. This could also be an influence on strategies for future screening, treatment and diagnosis.
The study received funding support from the National Institute of Mental Health, the National Alliance for Research on Schizophrenia and Depression, the University of Michigan Department of Psychiatry Research Committee and fMRI lab, the Richard Tam Foundation and the U-M Depression Center's Heinz C. Prechter Biopar Research Fund.
Scott Langenecker, Erica Dawson, Jon-Kar Zubieta, Michelle Kassel, Melvin McInnis, Anne Weldon, Sara Weisenbach, David Marshall, Aaron Vederman, Kortni Meyers and Laura Gabriel also contributed to the study.
Photo: Darcy Adelaide | Flickr