Individuals with Williams syndrome are hypersocial and lack normal social anxiety, but they frequently have exaggerated non-social fears. Andreas Meyer-Lindenberg of the National Institute of Mental Health in Bethesda, Maryland, and colleagues write in the August issue of Nature Neuroscience that the region of the brain that senses danger is functional in Williams syndrome but is not properly regulated.
The team asked individuals with Williams and healthy control subjects to perform matching tasks. They were asked to match images either of faces, which could trigger social fears because of the presence of angry faces, or scenes, which included pictures of nonsocial objects such as sharks. During the task, brain activity was measured using functional magnetic resonance imaging.
The amygdala was activated in both groups, but in response to different stimuli. The controls had more amygdala activity during the face-matching task, while individuals with Williams syndrome had more amygdala activity during the nonsocial matching task.
Because the amygdala was activated in both groups, but by different stimuli, the researchers reasoned that the neural regulation of the response and, thus, the perceived importance of the stimuli might be different in the two groups. Looking at the rest of the brain, they found that while the orbitofrontal cortex is activated during the face-matching task in normal controls, it was not stimulated in people with Williams syndrome.
The orbitofrontal cortex is responsible for assessing social relevance and regulating the amygdala, so a lack of activity in that region correlates well with Williams syndrome traits.
Previous theories about what goes wrong in Williams syndrome suggested that the amygdala was unable to function. These data refute that theory and suggest that higher brain processes required to regulate the amygdala are broken, says Meyer-Lindenberg. He also notes that while biological control of social behavior is well-known, this is the first time a neural mechanism for a genetically controlled circuit for social behavior has been mapped.