Which hypothesis is supported by functional MRI studies for both manic and depressive phases of bipolar disorder?

The dopamine hypothesis is supported by functional MRI studies for both manic and depressive phases of bipolar disorder due to the role of dopamine as a key neurotransmitter involved in mood regulation and reward response. Research utilizing functional MRI has demonstrated altered brain activity patterns in areas associated with dopamine transmission, such as the striatum and prefrontal cortex, during mood episodes in individuals with bipolar disorder.

In the manic phase, there is often heightened dopaminergic activity, which is associated with increased energy, euphoria, and impulsivity. Conversely, in the depressive phase, altered dopamine function may contribute to decreased motivation, anhedonia, and other depressive symptoms. Thus, the functional imaging findings illustrate how fluctuations in dopamine neurotransmission can influence the mood swings characterizing bipolar disorder.

While other theories, such as monoamine dysregulation, genetic predisposition, and stress-vulnerability, address relevant aspects of bipolar disorder, they do not have the same direct backing from functional MRI studies regarding both phases of the illness as the dopamine hypothesis does. This makes the dopamine hypothesis particularly strong in understanding the neurobiological underpinnings of bipolar disorder across different mood states.