People with depression or bipolar disorder often feel their thinking ability has gotten "fuzzy", or less sharp than before their symptoms began, and a new study published in BRAIN finds that the effect is real - and rooted in brain activity differences that show up on advanced brain scans.
The authors also say that these conditions both fall on a spectrum of mood disorders, rather than being completely unrelated. The study is of tests they gave to 612 women, more than two-thirds of whom had experienced either major depression or bipolar disorder. The researchers also present data from detailed brain scans of 52 of the women, who took tests while brain scans were conducted. The research involved 150 healthy women, 266 women with major depression that was either active or inactive at the time of testing, and 202 women with bipolar disorder who were not in a manic state when tested. All participants took a test that measures the ability to sustain attention and respond quickly - to focus one's brain, in essence. Then, 17 of the healthy women, 19 of the depressed women and 16 of the bipolar women took the same test again inside an fMRI scanner.
The fMRI group is still too small to make real conclusions but the sample size is large for this kind of mental health study, a field which is often beset with small numbers and inconsistent statistics. They focused on results from women to take gender differences out of the mix.
Seen as groups, women with depression or bipolar disorder did equally badly on the test, which required sustained concentration. 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.
Citation: Brain, May 2015, DOI: 10.1093/brain/awv070