Scientists are continuing to uncover the many mechanisms that underlie bipolar disorder. The exact cause of bipolar disorder is not known, but studies have found abnormalities in brain structure, in brain chemical production and function, and in nerve-to-nerve communication in parts of the brain that regulate mood and impulse control.
Because bipolar disorder tends to run in families, researchers are trying to find genes that are linked to bipolar disorder. For example, they have found that having the gene GNB1L on chromosome 22 increases susceptibility to bipolar disorder and that bipolar disorder is associated with differences in the CLOCK gene that helps regulate the body’s biological rhythms, as well as a variation in the gene CACNA1C, which is linked to smaller volume in the brainstem, a part of the brain that helps regulate mood and underlies cognition.
Brain imaging and other types of studies are helping uncover differences in the brains of people with bipolar disorder compared to those without the disorder. While the significance of these differences is still uncertain, some notable discoveries have been made.
- In people with bipolar disorder, studies have detected blood flow and structural differences in parts of the brain that regulate mood and impulse control.
- While examining people with bipolar disorder, scientists have also found evidence of the loss or damage of brain cells in the hippocampus—a part of the brain associated with memory—that indirectly affects mood and impulse control.
- Other studies have found an abnormal pattern of brain development in children with bipolar disorder that raises the risk for unstable moods.
- A recent body of research suggests that mitochondrial dysfunction may play a role in the development of psychiatric diseases, including bipolar disorder. Mitochondria are the energy-generating furnaces found in every cell, so when they do not work properly, the result is abnormally low energy production. Alterations in brain energy metabolism may result in the abnormal brain function and behaviors we see in patients with psychiatric disorders.
Neurotransmitters are naturally occurring chemicals in the brain and nervous system that facilitate the communication between cells. In examining people with bipolar disorder, researchers have found hindered production and function of the neurotransmitters serotonin and acetylcholine. There are also structural differences in the receptors for two other neurotransmitters, glutamate and GABA. All of these brain chemicals play important roles in mood regulation.