Question: Does a specific chemical imbalance or other brain abnormality cause bipolar disorder?
Answer: A number of irregularities or abnormalities have been detected in persons with bipolar illness.
These include neurologic, molecular, neurochemical, and hormonal abnormalities. The challenge has been to determine which of those factors may actually have a causal or etiologic role in which they are simply associated, or perhaps the result of the illness itself. So it's a very active area of investigation, one that no doubt will go on for decades to come.