Based on brain scans, which of the following is true of brain function and mood?

a. The brain is more active during manic episodes and less active during depressive episodes.

b. The brain is less active during manic episodes and more active during depressive episodes.

c. There is no consistent relationship between brain activity and mood.

d. The brain is more active than normal during both manic and depressive episodes.

e. The brain is less active than normal during both manic and depressive episodes.