In the first part we described the symptoms of bipolar disorder, its variant forms, the role of heredity, and the most common drug treatments. Here we go on to discuss brain function in bipolar disorder, the uses of psychotherapy, and the future of research. Most of what we know about the biology of mood swings is derived from brain scans, autopsies, and research on the effects and mechanisms of antidepressant and mood stabilizing drugs. Depression is associated with low activity in the brain as a whole and especially in the frontal cortex, the seat of planning and decision-making. At the same time, it activates the amygdala, a region where memories of emotionally significant events are maintained and learned stress responses are generated.
Mania is associated with increased blood flow and energy consumption in the cerebral cortex.
But the results of brain scans and autopsies are often inconsistent or ambiguous, and subtle abnormalities are uncovered only when scientists compare many brains and compute averages. Because they have not found anything that clearly distinguishes bipolar disorder from other brain diseases and malfunctions, brain imaging cannot be used to make the diagnosis. More is known about how mood is influenced by the chemical transmission of brain signals. In some of the most important brain systems that regulate mood, arousal, and energy, the monoamine transmitters norepinephrine, dopamine, and serotonin are used to pass signals between neurons. Any of these systems can be overactive or sluggish or function erratically.