Researchers at Japan's Brain Science Institute say there is good documentation for a link between bipolar disorder and mitochondrial dysfunction in brain nerve cells. Mice with mitochondrial dysfunction in brain cells had a disrupted diurnal rhythm and did not stop their activity overnight. The researchers suggest that a similar mechanism may be at play here as during mania, one of the symptoms of which is insomnia. The researchers hope that this research will help to understand the mechanism of bipolar disorder, which will contribute to the introduction of more effective treatments.