In 1939, heinrich kluver and paul bucy surgically lesioned this part of the brain, which eliminated defensive responses in various mammal species.

The correct answer is the amygdala.  

The fear response begins in the brain and scatters all through the body to make amendments for the flight reaction or best defense. The response of fear initiates in the part of the brain known as the amygdala. It is the almond-shaped arrangement of nuclei in the temporal lobe of the brain and is involved in determining the emotional silence of the stimuli.  

For example, the amygdala gets stimulated whenever one witnesses a human face with an emotion. This response is more noticeable with fear and anger. A threat sign, like the sight of a predator, initiates a fear reaction in the amygdala that stimulates the regions taking part in preparation for motor activities taking part in flight or fight.  

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