According to Dr. Sanjay Gupta from CNN on Student News today, bipolar or manic disorder is caused by hyper active amygdala in the brain while prefrontal cortex is blocked from activity. The reverse case would be for depression.
I do wonder, how people have often confused the difference between the Why and the How. "How" is pertaining to the definition of the matter, the obvious, that which scientists love, while "Why" has little if not nothing to do with the How because the interest of it has to be beyond the How. The Why is something the liberals today are disgusted by.
Thus, they could believe in a gay gene without concrete evidence, since the how is same as the why to them. Bipolar & depression were also considered by them as mental disorder in general. All this because the Why imploded into the How for them, they were confused of the Why. Yet, they call the Bible fairy tale because they cannot discern the How in the Bible, the How exploded beyond the Why for them.