Quiet: The Power of Introverts in a World That Can't Stop Talking

by Susan Cain

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. In humans with unwarranted fears, like batophobia, or fear of heights, the same thing happens. Repeated trips to the top of the Empire State Building seem to extinguish the fear, but it may come roaring back during times of stress—when the cortex has other things to do than soothe an excitable amygdala.