"The anterior cingulate fires up as the end result of a series of events. First, estrogen levels fall. Meanwhile, serotonin, the feel-good neurotransmitter, also decreases. The deficiency in serotonin causes the anterior cingulate gyrus to fire up. To make things worse, just about this time the PFC tends to quiet down, which is why women may have a hard time focusing and controlling impulses. So we see emotional difficulties, intensified feelings of sadness, and disturbed sleep."