Fear: real and imagined

Like other animals, humans learn to fear harmful events, such as being attacked by a dog. But the ability to learn fear in the absence of direct experience — for example, by being told a story about a neighbour who has been attacked by a dog — is distinctively human. Fear causes more blood to flow to the amygdala, a small almond-shaped structure located deep in the cortex of the brain. In the April Nature Neuroscience, Elizabeth Phelps and colleagues at New York University report that real and imagined fear activate different halves of the amygdala (Nat Neurosci 2001, 4:437-441).

Phelps et al examined activity in the human amygdala using functional magnetic resonance imaging in combination with a task called instructed fear. Subjects were presented different coloured boxes and told that they may receive an electric shock when a particular colour was presented. They were told to...