People with depression or bipolar disorder often describe their thinking to be "fuzzy", or less sharp than before their symptoms began. Now, researchers from the University of Michigan Medical School and Depression Center have shown in a very large study that effect is indeed real - and rooted in brain activity differences that show up on advanced brain scans.
The researchers used powerful brain scanning to look at differences between those with bipolar disorder or depression, and those without, according to a press release. The results add to the mounting evidence that these conditions both fall on a spectrum of mood disorders, rather than being completely unrelated.
A group of 612 women - two-thirds of which had a previous diagnosis of depression or bipolar - were given brain scans and a test. The test asked them to react rapidly when certain letters flashed briefly on a screen, amid a random sequence of other letters. Compared with the group with no mental health conditions, the groups with either diagnosis lagged noticeably on this standard test of cognitive control.
And while many individual women with depression or bipolar scored as well on the test as healthy participants, nearly all the test-takers in the bottom 5 percent of performers had one of the two mood disorders.
On the brain scans, the researchers found that the women with depression or bipolar disorder had different levels of activity than healthy women in a particular area of the brain called the right posterior parietal cortex. In those with depression, the activity in this area was higher than in healthy individuals, while in those with bipolar disorder it was lower. The area where the differences were seen helps control "executive function" -- activities such as working memory, problem solving and reasoning.
"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," said lead author Kelly Ryan, a U-M neuropsychologist, according to the press release. "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. 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."
Reference: Brain, May 2015, DOI: https://dx.doi.org/10.1093/brain/awv070 https://brain.oxfordjournals.org/content/brain/138/5/1424.full.pdf (free online access)
Funding/Authors: National Alliance for Research on Schizophrenia and Depression, National Institute of Mental Health (MH074459), U-M Department of Psychiatry Research Committee and fMRI lab, Heinz C. Prechter Bipolar Research Fund at the U-M Depression Center and the Richard Tam Foundation. In addition to Ryan and Langenecker, the research team included several current and former students and fellows in the U-M Department of Psychiatry, and faculty members Melvin McInnis, M.D., and Jon-Kar Zubieta, M.D., Ph.D.
