Brain wiring explains how siblings avoid bipolar disorder despite high risk

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Source: Alfred Anwander, Max Planck Institute for Human Cognitive and Brain Sciences, Wellcome Images

Bipolar disorder is believed to be deeply rooted in genetics, meaning it can be passed hereditarily through family members. There’s just one thing that has always confused researchers. If bipolar disorder is genetic, how do siblings avoid experiencing the same mental illness as their brother or sister?

Researchers from the Icahn School of Medicine at Mount Sinai say they have finally figured out the answer and it may pave the way for more effective treatments for the disorder in the future.

According to the report published in the American Journal of Psychiatry, the brains of siblings often show signs of an adaptation that makes them more resilient to the disorder.

Bipolar disorder is a condition linked to long periods of extreme moods or shifting from unusual happiness to severe depression. It can affect activity levels and impair a person’s ability to live their day-to-day life and is estimated to affect approximately 5.7 million Americans over 18-years-old every year.

Siblings of people with bipolar disorder are up to four times more likely to develop the disorder compared to the average person, but that still leaves many siblings without the mental illness. To examine why so many were able to avoid bipolar disorder when they are genetically predisposed to it, the team of researchers examined functional magnetic resonance imaging (fMRI) scans from 78 patients with bipolar disorder and 64 of their siblings without the condition. Their scans were then compared to a control group of 41 non-related people who did not have bipolar disorder.

The findings showed that the siblings without bipolar disorder showed signs of abnormal connectivity in brain regions associated with sensation and movement. This abnormal connectivity is typically found in individuals with bipolar disorder, however, the siblings compensated by also having uniquely increased connectivity in the “default mode network” (DMN) of the brain.

According to a press release on the recent discovery, the DMN is a network of interacting brain regions known to have activity highly correlated with each other and distinct from other networks in the brain.

While this information may help satisfy scientific curiosity, it could also provide the foundation for future treatments that could “rewire the brain.”

“Most of the risk factors for bipolar disorder, including genetic risk, early childhood adversity, and trauma, are not modifiable,” said the study’s senior author Sophia Frangou, M.D., Ph.D., a professor of psychiatry at the Icahn School of Medicine at Mount Sinai.

“By contrast, this research shows that the brain can modify its connectivity to overcome biological adversity. This gives hope that we can harness this natural brain potential to develop preventive interventions.”

To test if this approach may be viable, the team is beginning a set of follow-up experiments designed to use simple computerized tasks to enhance brain connectivity. Based on their early findings, the researchers say the simple treatment may help restore brain connectivity in some regions and reduce symptoms of bipolar disorder.

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