[ELI5] What happens in the brain of someone suffering from bipolar disorder that creates such a divide between moods and why does it happen in cycles?

Question

[ELI5] What happens in the brain of someone suffering from bipolar disorder that creates such a divide between moods and why does it happen in cycles?

In: Biology

Answer 1

In our brain we have several different areas, many of them are called cortexes for example the central motor cortex is where the signal to move body parts comes from.
With mood disorders such as bipolar disorder we want to think about where is our “mood” or emotion coming from. Thus, we find ourselves talking about a less well known deep part of the brain called the limbic cortex. The limbic cortex is the part of the brain commonly associated with processing emotion.

A major function the limbic cortex performs is allowing the reward pathway of dopamine to occur. Dopamine is in short the chemical that your brain produces to make you feel happy, if it’s there in excess you might feel elated, be less socially restricted, and very excitable. If dopamine is not as present you might feel less happy, less excitable, etc.

Normally your brain regulates all of the chemicals in your body with relative accuracy due to various fail-safes and sensors throughout the body, this regulation is called homeostasis. Bipolar disorder is basically the answer to what happens if the system for maintaining dopamine’s homeostasis in our body was broken.

Basically in someone with bipolar disorder there brain might not get the signal to stop producing or receiving dopamine, so it becomes present in excess in the body resulting in an extreme emotional high. Then their body might eventually figure out “oh, it’s time to turn down the dopamine” so the system returns to normal and the person returns to baseline. Or it could get to the point where the body exhausts the resources to produce dopamine triggering an absence and therefore an extreme low. Hence the divide between the moods and the cycling.

In sum, the ability for the brain to manage the level of dopamine is likely broken somehow and so the levels fluctuate widely. Why the states maintain for a while or you can cycle back to baseline is basically the brain desperately trying and failing to achieve homeostasis.