Fuzzy thinking could play a significant role in the onset of depression, according to a new study from the University of Michigan. This research could also pave the way to a new way of thinking about mood disorders.

People experiencing depression often report feelings of "fuzzy thinking" compared with their cognitive abilities previous to the time when they developed symptoms of depression. This experience has now been revealed in brain scans for the first time ever.

Researchers examined medical records of 612 women, of whom two-thirds experienced depression or bipolar disorder at some point in their life. Brain scans were also conducted on 52 of the subjects as they took tests.

The subjects were exposed to flashing letters and had to take actions based on the appearance of letters and sequences. Those with bipolar disorder and depression were found to have similar challenges with the tests when compared with results from people with neither condition. Nearly all of the women who finished in the bottom 5 percent in test results had been diagnosed with one or both conditions.

A number of health professionals are of the belief that depression and fuzzy thinking are not completely separate conditions but are points along a spectrum of mood disorders. This study lends evidence to this notion. If the idea that mood disorders should be thought of more as a spectrum than isolated conditions gains wider acceptance, the change could result in new diagnostic and treatment methods.

"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," Kelly Ryan of the University of Michigan said.

Unusual levels of activity were recorded in the right posterior parietal cortex in the brains of subjects, which normally helps direct planned movements. Activity levels were lower than normal in bipolar patients and higher in those with depression.

Executive functions such as reasoning, problem solving and working memory were found to be affected in subjects with the mental disorders.

The National Institute of Mental Health has identified the idea of a spectrum of mood disorders for further investigation, labeling it as research domain criteria (RDoC).

Investigators limited their study to females in order to reduce the effect of gender biases in the study.

Other mood disorders, including anxiety, are also believed to lie at some point along the spectrum, according to the new way of thinking about the mind. However, further study will need to be carried out before brain scans could be utilize in forming diagnoses.

Analysis of a mood disorder spectrum and how depression and bipolar disorder are exhibited in women was published in the journal Brain.

Photo: Loren Kerns | Flickr