What is the main idea of the passage?

The passage discusses the role of the amygdala in fear and aggression, highlighting the findings that electrode stimulation of the amygdala can elicit extreme aggressive acts while patients with damage to this structure exhibit a complete absence of aggression. It emphasizes the increased knowledge and understanding of specific brain structures, particularly the amygdala, over the past two decades. Therefore, the main focus is on the understanding of the amygdala's impact on human emotions.