Researchers looking at the biology of bipolar disorder have many clues but no definitive answers about the unique chemistry of the bipolar brain. Genetics, chemical imbalances and the nature of bipolar brain function are all likely to play a role in the development of bipolar disorder.


Children with one parent who has bipolar disorder have a 20 percent chance of developing the condition, while children with parents who do not have bipolar disorder have only a four percent chance of developing the illness. Researchers do know that a single gene does not cause bipolar disorder; many genes, and their interactions with each other, are involved.

Biological Clock

People with bipolar disorder might have changes in the setting of the speed of their biological clock. The body’s internal biological clock not only controls sleep patterns but also controls the release of hormones and chemicals that regulate vital body functions, such as blood pressure and temperature. People with bipolar disorder may be particularly sensitive to disrupted sleep, including jet lag and shift work.

Bipolar Brain Function

Growing evidence about bipolar brain function supports that a region of the brain called the medial prefrontal cortex is underactive in people with bipolar disorder, even when they are having no symptoms. The medial prefrontal cortex is believed to be important for a person to be able to change behavior from a routine response to a new, flexible response based on circumstances.

Evidence also points to a part of the brain called the amygdala, which processes emotions, as possibly being smaller and hyperactive in people with bipolar disorder. But researchers don’t know if the altered size and function of the amygdala is a cause of bipolar disorder, or a result of the disease.

Also, researchers now know that the brain is highly “plastic,” meaning that it can change in response to the demands placed on it, including growing new cells in certain regions. Unfortunately, sustained depression appears to decrease the number of brain cells and the number of connections that brain cells make with each other.

Bipolar Brain Chemistry

Most researchers believe that bipolar disorder involves a chemical imbalance in the brain. Neurotransmitters are chemical messengers between nerve cells (neurons). The many different neurotransmitters that help regulate mood include:

  • Dopamine
  • GABA
  • Glutamate
  • Noradrenaline (norepinephrine)
  • Serotonin.

Imbalances of these neurotransmitters may cause mood symptoms. Many medications used to treat bipolar disorder target these neurotransmitters.

The brain also produces nerve growth factors, which are chemicals needed to help brain cells grow and connect to each other. Many bipolar medications work to boost these chemicals. Researchers continue to study the biology of bipolar disorder looking for more definitive answers about the bipolar brain.


Carmichael, M. (May 18, 2008). The Biology of bipolar disorder: What scientists have learned about the genetic and neurological roots of this complex illness. Retrieved May 17, 2010, from the Newsweek website:

Phelps, J. (August 2008). The biologic basis of bipolar disorder: Five mini-chapters on the brain chemistry of mania and depression. Retrieved May 17, 2010, from the Psych Education website:

International Society for Bipolar Disorders Staff. (n.d.). What causes bipolar disorder. Retrieved May 17, 2010, from the International Society for Bipolar Disorders website:

 Posted on : June 13, 2014