12.14 : Bipolar Disorder

Bipolar disorder is a chronic mental health condition marked by significant mood fluctuations, including episodes of mania and depression. Elevated energy levels, heightened mood or irritability, impulsive behavior, reduced sleep needs, rapid speech, racing thoughts, inflated self-esteem, and distractibility characterize mania. Individuals with bipolar disorder often alternate between depressive and manic states, with periods of emotional stability lasting an average of six months to a year. There are two types of bipolar disorder: Bipolar I involves at least one full manic episode, while Bipolar II includes hypomania (a milder form of mania) and at least one major depressive episode.

Genetic and Neurobiological Findings

Bipolar disorder exhibits a strong genetic basis, with heritability estimates ranging between 60% and 85%. Studies of identical twins demonstrate a 70% likelihood of shared diagnosis, compared to a greater than 10% probability among fraternal twins. This stark contrast underscores the role of shared genetic factors in its development. On a neurochemical level, imbalances in neurotransmitters such as dopamine, serotonin, and norepinephrine are implicated in the disorder. These neurotransmitters are critical for regulating mood and emotional responses, suggesting a biochemical foundation for the extreme mood variations seen in bipolar disorder. Studies link high levels of the neurotransmitter glutamate to bipolar disorder.

Neural Activity and Structural Findings

Advances in neuroimaging have identified distinct brain activity patterns in bipolar disorder. Heightened activity in the amygdala, a region associated with processing emotions, correlates with the intense emotional experiences characteristic of the disorder. Conversely, the prefrontal cortex, responsible for executive functions such as decision-making and impulse control, exhibits reduced activity and gray matter volume. These findings highlight the interplay between emotional dysregulation and impaired planning or inhibition in bipolar disorder.

Environmental Influences and Triggers

Environmental factors significantly influence the course of bipolar disorder. Stressful events are known to precipitate manic episodes, increase the likelihood of relapse, and hinder recovery. Surprisingly, positive events, such as personal achievements or promotions, can also act as triggers for mania. This dual sensitivity underscores the complexity of the disorder's triggers. Notably, bipolar disorder affects men and women at comparable rates, reflecting its broad impact across populations.