Siblings of bipolar people are resilient to the disorder thanks to hyperconnectivity of the default mode network in the brain, a recent study suggests.
People with bipolar disorder are subject to extreme mood shifts, from feeling "high" to feeling absolutely "down." They also experience abnormal fluctuations in their energy levels, which can lead to disrupted activity patterns.
In the United States, the yearly prevalence of bipolar disorder among adults is approximately 2.6 percent, according to the National Institute of Mental Health (NIMH).
The NIMH identify three main factors that put people at risk of bipolar disorder: genetic factors, environmental factors, and changes in the brain.
First-degree relatives of people with bipolar disorder have a 13-fold higher risk of developing the disorder themselves, some studies suggest. However, many siblings of people with bipolar disorder do not develop it themselves, although, genetically, they are at such a high risk.
Now, a team of researchers from the Icahn School of Medicine at Mount Sinai in New York City, NY, led by Dr. Sophia Frangou, has endeavored to reveal the reason behind siblings' resilience to the disorder, and to see whether or not this could help to develop better preventive interventions.
This new study is based on previous research conducted by the team of scientists over the past few years. As Dr. Frangou declared for Medical News Today, "Over the last 5 years, we have provided evidence that the brain of high-risk individuals for bipolar disorder shows adaptive (resilience-related) changes in individuals that remain well despite their genetic risk."
"This paper extends this research to show that these adaptive changes are also detectable in the basic functional brain architecture of resilient individuals."
Dr. Sophia Frangou
Their findings were reported today in the American Journal of Psychiatry and are available online.
Resilience linked with DMN connectivity
The researchers used functional MRI to examine the brain activity of 78 people diagnosed with bipolar disorder, as well as 64 of their siblings that had not developed the disorder, and 41 healthy participants who were not related to anyone else in the cohort.
It was found that the siblings' brains exhibited hyperconnectivity in the sensorimotor network, which are the brain regions concerned with perceiving sensations and coordinating movement. This was consistent with the findings of previous research.
What was more interesting was that hyperconnectivity was also noted in the default mode network (DMN) of the siblings monitored, which counterbalanced the abnormal activity in the sensorimotor network. DMN hyperconnectivity was absent in the brains of the participants with bipolar disorder, suggesting that this was what made their siblings resilient to the condition.
The DMN is a fairly new addition to neuroscientific vocabulary, so consistent definitions of it can be hard to come by. Nevertheless, in general terms, it could be characterized as a network of brain regions that interact with each other even when other brain regions are at rest.
As Dr. Frangou explained for MNT, "The DMN is considered the functional backbone of the brain. This network is most active during spontaneous thought and represent[s] the brain's baseline configuration."
"The DMN," she adds, "contributes and facilitates changes in the functional configuration when we switch from spontaneous to task-related thoughts. The study therefore shows that resilience is associated with adaptive brain changes in the brain's core network."
Potential to tap into 'adaptive brain changes'
The team hopes that their discovery might open up new avenues for research into the respective brain mechanisms that either promote or are resilient to bipolar disorder.
If stronger activity in the DMN is what grants some siblings of people with bipolar disorder their resistance to the disorder, then they hope that, by unearthing the specifics of this mechanism, they may be able to enhance the plasticity of both the DMN and the sensorimotor networks in individuals prone to bipolar disorder.
"We have an active research study to test whether we can use computer-based simple mental exercises to restore the functional architecture of the brain in patients and in high-risk individuals," Dr. Frangou told MNT.
She added that the team have full confidence in the results of their current study, and that, going forward, they are eager to find out when this adaptive brain mechanism is kick-started in siblings of people with bipolar disorder.
Dr. Frangou concludes, "The study results are very robust as we have a large sample size and the findings reflect adaptive brain changes that we have shown in another independent sample. What we need to do next is to trace these adaptive changes along the lifespan to find out when these adaptive changes are first observable."