“But the frontal cortex isn’t all-powerful; it doesn’t switch the amygdala off altogether. In one study, scientists conditioned a rat to associate a certain sound with an electrical shock. Then they played that sound over and over again without administering the shock, until the rats lost their fear. But it turned out that this “unlearning” was not as complete as the scientists first thought. When they severed the neural connections between the rats’ cortex and amygdala, the rats became afraid of the sound again. This was because the fear conditioning had been suppressed by the activity of the cortex, but was still present in the amygdala.”