What Causes Bipolar Disorder?
Kimberly Bailey, About.com
We have all asked this question at some time. I've heard explanations ranging from a shortage of Lithium in the brain to dog bites in childhood! Obviously, there is a great deal of misinformation to be had.
To compound the confusion, legitimate scientific research continues to publish new information and hypotheses. A newly published study in the American Journal of Psychiatry reports "in those with bipolar disorder, two major areas of the brain contain 30 percent more cells that send signals to other brain cells." This report theorizes that "the extra signal-sending cells may lead to a kind of overstimulation, which makes sense considering the symptoms of bipolar disorder (1)."
But has anyone found the true cause of bipolar disorder? It would be wonderful to say that X or Y was the cause, but the answer is not that simple.
According to Durand and Barlow, most scientists believe that "psychological disorders are always the products of multiple interacting causal factors"(2). As it relates to bipolar disorder, these causal factors are usually divided into biological and psychological explanations. In plain English, psychopathology is the study of significant causes and processes in the development of mental illness, which means there are physical and mental / environmental / emotional causes for mental illnesses.
In considering the biological explanations, the first issue is inheritability. This question has been researched via multiple family, adoption and twin studies. In families of persons with bipolar disorder, first-degree relatives (parents, children, siblings) are more likely to have a mood disorder than the relatives of those who do not have bipolar disorder (3). Twin studies indicate that "if one twin presents with a mood disorder, an identical twin is approximately three times more likely than a fraternal twin to have a mood disorder (2)." In considering bipolar disorder specifically, the concordance rate (when both twins have the disorder) is 80% for identical twins, as compared to only 16% for fraternal twins (2). "Overwhelming evidence suggests that such disorders are familial and almost certainly reflect an underlying genetic vulnerability (2)."
However, exactly what is inherited? The neurotransmitter system has received a great deal of attention as a possible cause of bipolar disorder. Researchers have known for decades that a link exists between neurotransmitters and mood disorders, because drugs which alter these transmitters also relieve mood disorders (4). Some studies hypothesize that a low or high level of a specific neurotransmitter such as serotonin, norepinephrine or dopamine is the cause. Others indicate that an imbalance of these substances is the problem - i.e., that a specific level of a neurotransmitter is not as important as its amount in relation to the other neurotransmitters (2). Still other studies have found evidence that a change in the sensitivity of the receptors on nerve cells may be the issue (4). In short, researchers are quite certain that the neurotransmitter system is at least part of the cause of bipolar disorder, but further research is still needed to define its exact role.
The primary psychological culprit implicated in the manifestation of bipolar disorder is stressful life events. These can range from a death in the family to the loss of a job, from the birth of a child to a move. It can be pretty much anything, but it cannot be precisely defined, since one person's stress may be another person's piece of cake. With that in mind, research has found that stressful life events can lead to the onset of symptoms in bipolar disorder. However, once the disorder is triggered and progresses, "it seems to develop a life of its own. Once the cycle begins, a psychological or pathophysiological process takes over and ensures that the disorder will continue (2)."
When we look for the cause of bipolar disorder, the best explanation via the research available at this time is what is termed the "Diathesis-Stress Model." The word diathesis means, in simplified terms, a bodily condition that make a person more than usually susceptible to certain diseases. Thus the Diathesis-Stress Model says that "each person inherits certain physical predispositions that leave him or her vulnerable to problems that may or may not appear, depending on what kinds of situations that person confronts (4)." Durand and Barlow define this model as a "hypothesis that both an inherited tendency and specific stressful conditions are required to produce a disorder (2)."
So the bottom line, according to today's thinking, is that if you are manic depressive, you were born with the possibility of developing this disorder, and something in your life set it off. But scientists could refine that theory tomorrow. The one sure thing is, they won't give up looking for answers.
(1)The University of Michigan. (October, 2000). Evidence of Brain Chemistry Abnormalities in Bipolar Disorder.
(2)Durand, V. M. & Barlow, D. H. (2000). Abnormal Psychology: An Introduction. Scarborough, Ontario: Wadsworth.
(3)Davis, S. F., & Palladino, J. J. (2000). Psychology (3rd ed.). Upper Saddle River, NJ: Prentice-Hall, Inc.
(4)Bernstein, D. A., Clarke-Stewart, A., Penner, L. A., Roy, E. J., & Wickens, C. D. (2000). Psychology (5th ed.). Boston, MA: Houghton Mifflin Company.