New Evidence of the Interconnectedness of Depression and Bipolar Disorder

Two new studies delve into the “fuzzy thinking” and sadness experienced with both mood disorders. (Photo: Stocksy/Marcel)

Researchers are increasingly investigating the idea that mood disorders may fall along a spectrum, rather than comprise distinct, unrelated diagnoses. And now, two new studies reveal further links between bipolar disorder and depression.

To be clear, the conditions do have different symptoms: “With bipolar disorder, there are fluctuations in mood,”Kelly Ryan, PhD, a University of Michigan neuropsychologist and clinical assistant professor in the U-M Department of Psychiatry, tells Yahoo Health. “Sufferers have a period of euphoria, followed by deep depression — but we don’t see the mania in those with major depressive disorder.”

But Ryan found in her new study, published in the journal BRAIN, evidence that the two conditions are interconnected. The study examined a common complaint of both people with depression and people with bipolar disorder: “fuzzy” thinking, or worsening concentration before the onset of their symptoms.

The study included 612 women, including those with depression or bipolar disorder, and those without a mental condition. They were administered tests, which involved reacting quickly to letters sequenced on a computer screen.

As a group, those with a mood disorder did equally poorly on the exam, which required extended concentration to react quickly to the letters. And compared with those without a mood disorder, those with depression or bipolar generally performed worse on the tests. (Some with either condition did as well as the healthy people, but the bottom 5 percent of test-takers all had one of the two mood disorders.)

As a separate part of the experiment, researchers also put 52 women under a brain scanner while the tests were in progress. Women with depression or bipolar disorder had different levels of cognitive activity in an area of the brain called the posterior parietal cortex, which controls all-important executive functioning.

Related: Bipolar Disorder: What You Need To Know

Interestingly, those with depression had higher brain activity than healthy test-takers, while those with bipolar disorder had lower, says Ryan. It’s a finding they would have never found without the brain scans. “Those with major depression had overactivity, whereas those with bipolar disorder had underactivity,”she explains, “yet they showed the same pattern of activation based only on performance on the task.”

The varying activity in the same area of the brain does hint at a continuum. “The take-home message is that these two conditions may fall along a spectrum instead of two distinct disorders,”Ryan says. “The NIMH [National Institute of Mental Health] has been pushing this research domain.”

Another new study in JAMA Psychiatry also dug into the similarities and differences between the disorders, since clinicians oftentimes have difficulty distinguishing those with bipolar and unipolar depression during the low times. This study showed that people with bipolar disorder, while in a depressed state, experience depression differently than people with the diagnosed condition of depression.

The researchers looked into how medication-free individuals with the conditions regulated their emotions in depressed and remitted states. They had 42 people with major depressive disorder, 35 with bipolar disorder, and 36 healthy individuals rate their emotions after looking at emotional photos (ranging from negative and sad, to positive and upbeat).

Related: The Number One Cause Of Depression – Everywhere

While they were in a normal state and not on medication, those with bipolar disorder were worse at regulating both happy and sad emotions. While depressed, they were better at regulating happy emotions. Both groups were pretty consistent in regulating sad emotions while experiencing a bout of depression.

Then, they scanned the brains of these individuals while they viewed the emotionally fueled photographs. Here, the researchers saw differences in the amount of brain activity in areas that control emotions. While not depressed, those with bipolar disorder showed spikes in the area guiding emotions, called the dorsolateral prefrontal cortex. This indicates bipolar men and women work harder to regulate and control their emotions than those with clinical depression.

On the flipside, while depressed, those with bipolar disorder showed a marked decrease in rostral anterior cingulate cortex activity, which serves as the link between the brain’s cognitive and emotional centers. In essence, while those with major depressive disorder and bipolar disorder might appear the same while in a depressed state, the differences in brain activity shows they’re experiencing and controlling emotions differently.

Ryan says there will be more research to follow to better understand, diagnose, and treat mood disorders. She says scientists will look at other cognitive areas that might show disease markers, and delve further into the neurobiology for connections. Genetics and behavioral responses will also be examined. “If we can somehow link all those, we’ll have a better understanding of how to approach these disorders,” she says.

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