Women "of a certain age" worry that fuzzy thinking - the inability to remember or focus - may be a symptom of Alzheimer's disease or some other form of dementia. Instead, a study at the University of Michigan in Ann Arbor suggests that it is a symptom of depression and bipolar disorder. The study, reported in the journal Brain, even puts these conditions on a continuum.
As reported by David McNamee in Medical News Today (May 5, 2015), a large study of brain scans showed that impaired executive function, or fuzzy thinking, indicates the mood disorders. Instead of being totally separate conditions, they "exist as points on a spectrum," McNamee said.
The researchers recruited 618 women, 150 of whom were healthy, 266 of whom had the diagnosis of major depression and 202 of whom had bipolar disorder but were not manic at the time of the study. Only female subjects were used to avoid gender differences in the study.
Participants were tested for their ability to maintain their attention and respond to situations quickly. They had to "respond rapidly when certain letters flashed up on a screen, amid a random sequence of other letters," McNamee said.
While women exhibiting depression performed as well as those exhibiting bipolar disorder, both groups performed worse than those without mental health disorders. With a few discrepancies, people with bipolar disorder or depression had scores in the bottom 5 percent.
The next phase of the study was a functional magnetic resonance imaging (fMRI) scan administered to a small sample of the healthy, depressed and bipolar women. Researchers determined that women with mood disorders demonstrated lower levels of activity than the control group in the right posterior parietal cortex, the part of the brain that controls working memory, reasoning and problem solving.
Kelly Ryan, Ph.D., the lead author of the article and a neuropsychologist at the University of Michigan, said that the study demonstrated "a shared cognitive dysfunction in women with mood disorders, which were pronounced in the cognitive control tests and more nuanced in scans." He added that, ""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."
Now that scientists are looking at psychiatric disorders as a continuum instead of as discrete conditions, the National Institute of Mental Health has created an initiative called Research Domain Criteria (RDoC).
As explained by the paper's senior author, Scott Langenecker, Ph.D., "The RDoC initiative is not meant to replace this clinical diagnostic system. It is designed to extend ways of understanding neurobiology, performance and genetics at natures' seams, rather than at groupings of clinical symptoms based on a patient's current memory of recent symptoms and clinician observations of signs. The RDoC initiative is a recognition that we need to rely more heavily on what these neurobiological results are telling us - mental diseases have more overlap in the basic brain and genetic signatures."
Scientists conducting future tests can save money on fMRI testing by starting with cognitive control tests. The fMRI would be reserved for those who perform poorly.
Source: Medical News Today