FuturePundit: Gene Version Prevents Cingulate From Suppressing Amygdala Fear Response
In most people the cingulate downregulates the amygdala. In persons with short copies of the serotonin transporter gene this downregulation fails. The active amygdala produces the sensation of anxiety.
SSRIs act by altering the production of the serotonin transporter protein, thus their delayed therapeutic benefit.
This appears to be a significant breakthrough.