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- [Voiceover] There are a number of different theories about the cause of Bipolar Disorder. As with everything else though, there is probably no one cause. Instead there are many causes that interact with each other in complicated ways. And I even think that the term cause is problematic in this situation, because it kind of implies that everyone who is exposed to X, Y and Z causes will definitely wind up with this disorder, but that isn't the case either. Think about seasonal allergies. Multiple people might be exposed to pollen, but not everyone has them. It depends on certain factors like your individual immune system. And also behavioral things, like where you live. So while in certain situations pollen might be required for certain seasonal allergies to exist there are many things that can increase or decrease the likelihood that you'll feel sick. And so in this case, it might be more appropriate to talk about risk factors than to talk about causes. And that's true of bipolar disorder as well. So we are going to be talking about things that increase the likelihood that someone will develop bipolar disorder, but aren't guaranteed causes. We'll specifically be looking at biological risk factors, psychological risk factors, and environmental risk factors. And in terms of these biological risk factors I'm going to further divide them into genetic risk factors, neurochemical imbalances, and differences in brain structure and function. In terms of genetics, family studies, twin studies, and adoption studies have all shown that there is a very strong genetic component to bipolar disorder. Even more so than for depression. In fact, someone who has a family member with bipolar disorder is actually 10 times as likely to have the disorder themselves as compared to the general population. We know that adopted children are more similar to their biological parents than their adoptive parents in terms of bipolar rates, and this indicates a genetic cause rather than an environmental one. We also know that identical twins have more similar rates of the disorder than fraternal twins or other siblings. But once again, this isn't a guarantee. Rates are higher for identical twins, but they are not identical. One identical twin having bipolar disorder does not 100% guarantee that the other twin will have it as well. It just increases the likelihood of it. So while genes certainly do play a role, the situation is pretty complicated. There isn't just one bipolar gene that guarantees that someone will wind up with bipolar disorder. In terms of neurochemical imbalances, we know that individuals with a related disorder, major depressive disorder, we know that they show decreased levels of certain monoamine neurotransmitters. And this includes serotonin, norepinephrine, and dopamine. And so it's been hypothesized that increased levels of these neurotransmitters might be related to mania. However, other researchers disagree and think that this model is too simplistic. So this is an area of active research, and knowledge about the neurochemical underpinnings of bipolar disorder will continue to evolve over time. We may not be totally sure what's going on at the neurochemical level, but we can use structural and functional imaging to look at neurological differences between individuals with bipolar disorder and individuals without it. For example, some studies have found differences in functioning in the prefrontal cortex, which is the area of the brain that deals with higher order cognition. Other studies also look at changes in the lymbic system, or the area of our brain that process emotion. There is also some evidence that individuals with bipolar disorder show an increase in volume in the ventricles in their brain. These are the cavities toward the center of the brain where cerebral spinal fluid is produced and stored. Another biological factor might be disturbances in circadian rhythms. During a manic episode an individual has a ton of energy and they feel a decreased need for sleep. And while we tend to think of these things as symptoms of bipolar disorder, it is possible that these circadian rhythm disturbances might somehow be a cause of the disorder rather than a symptom. Now lets move on to talk about psychological risk factors. One thing that scientists have noticed is that individuals with bipolar disorder tend to have other psychological disorders as well. So it's comorbid with other conditions. This includes things like anxiety disorders, like generalized anxiety disorder and social anxiety disorder. These individuals are also more likely to have substance use disorders, to abuse drugs and alcohol, but it's unclear if that's something that naturally co-occurs with bipolar disorder or something that is caused by it. Because it's possible that individuals with bipolar disorder might use substances more because they're trying to self-medicate. So that, rather than any kind of biological predisposition, could be driving the effect. This is kind of true for all of these disorders. We might see them at the same time, but we don't really know if one triggers the other. And we don't know if there's any kind of common biological cause. In general though, researchers believe that these psychological factors aren't the most important triggers for bipolar disorder, and that environmental risk factors might play a much larger role. Going through a major life stressor is one of the greatest predictors for a manic episode, and this seems to be especially true for stressors related to social interactions. But please note that this does not mean that going through something stressful like a divorce will suddenly cause someone to develop bipolar disorder. Instead we're saying that they can trigger manic episodes for individuals who are already at risk. Another thing I want to note is that these stressful life events aren't just the things that you might normally think of when you think about stressors. So it might be helpful when you see this word to mentally replace it with major life changes. So these stressors could include losing a job, but they could also include starting a new one, or going to college, or getting married. There also seem to be a number of other environmental factors that can lead to manic episodes in people who are already at risk. For example, taking certain antidepressants can actually trigger a manic episode. This is one of the many reasons why people who go on antidepressants, specifically SSRIs, are carefully monitored by their physicians. So I've separated these risk factors into biological, psychological, and environmental factors, but in order to really have a comprehensive picture of this you need to think of all of them as being related to each other, or building on each other. So if I had to give you one kind of take-away line for this video, if I had to give you some kind of hard and fast cause, I would say that bipolar disorder is caused by a biological predisposition in combination with specific psychological and environmental factors.