Stanford psychologist Laura Carstensen, to name one such example, used an fMRI scanner to study the brain behavior of subjects presented with both positive and negative imagery. She found that for young people, their amygdala (a center of emotion) fired with activity at both types of imagery. When she instead scanned the elderly, the amygdala fired only for the positive images. Carstensen hypothesizes that the elderly subjects had trained the prefrontal cortex to inhibit the amygdala in the presence of negative stimuli. These elderly subjects were not happier because their life circumstances
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