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In Brief: Brain pathways to fear

In Brief

Brain pathways to fear

A brain imaging study of people with the disorder known as Williams syndrome contributes to the understanding of human emotional processes by targeting a distinct circuit that governs anxiety associated with social situations.

Williams syndrome is a genetic disorder with symptoms that include unusual friendliness, empathy, and lack of social anxiety. People with the disorder are socially uninhibited and poor at reading social cues; for example, they often approach strangers and start conversations. But they are more susceptible than average to other kinds of anxiety and phobias.

Most people who have the disorder are mentally retarded, but the investigators recruited 10 with normal intelligence and compared them to controls as they performed two tasks: matching an angry or frightened face with another face showing the same expression, and matching a frightening scene without human beings (for example, a burning building or airplane crash) to an identical scene.

Both groups performed the tasks equally fast, but magnetic resonance imaging (MRI) suggested that they were using different parts of the brain. In controls, the amygdala, which recognizes and remembers frightening experiences, was activated most by the faces; in people with Williams syndrome, it was activated more by the scenes that did not include human beings.

The prefrontal cortex, a seat of decision-making and judgment, is thought to regulate the responses of the amygdala. When controls performed the face-matching task, which was more difficult, the prefrontal region became more active than it was in the scene-matching task, and the more active the prefrontal cortex was, the less active the amygdala. Different parts of the prefrontal cortex also responded differently. A more active dorsolateral prefrontal cortex was correlated with a more active orbitofrontal prefrontal cortex but a less active medial prefrontal cortex. The dorsolateral region is believed to be important for assigning emotional tone and value to situations, and the medial region is important for regulating empathy and anger.

In the people with Williams syndrome, the prefrontal cortex was equally active on both tasks, and the orbitofrontal region was relatively inactive. Damage to that region is associated with uninhibited social behavior. The Williams syndrome group showed high activity on both tasks only in the medial prefrontal cortex.

In people with Williams syndrome, the link between the orbitofrontal cortex and the amygdala was apparently interrupted, while the link to the medial prefrontal cortex was stronger. One result may have been their increased friendliness and poor social judgment.

Meyer-Lindenberg A, et al. "The Neural Correlates of Genetically Abnormal Social Cognition in the Williams Syndrome," Nature Neuroscience (August 2005): Vol. 8, No. 8, pp. 991–93.

Bhattacharjee Y. "Friendly Faces and Unusual Minds," Science (November 4, 2005): Vol. 310, pp. 802–04.

Last updated:	September 05, 2008