In Brain Sense, I tell the story of thirteen-year-old Charlie Betz (not his real name). Charlie has Williams syndrome. He is missing about twenty genes from chromosome #7. Twenty might not seem like many out of the 25,000 or so that it takes to make a human being, but they made a big difference in who Charlie is, what he loves, and what he can do.
Charlie can neither read nor write--probably never will learn the doctors say--although his vocabulary is large and he speaks with clarity and expression. His IQ has been measured at 60, but his social graces show no impairment. He's charming with people--bubbly, sociable, trusting--perhaps indiscriminately trusting--with everyone he meets, and he remembers everyone's face.
"The discrepancy between ... language ability and IQ [in individuals with Williams syndrome] is startling," says Ursula Bellugi, professor and director of the Laboratory of Cognitive Neuroscience at the Salk Institute, who has been studying the behavioral aspects of Williams syndrome for more than twenty years. "Children with Williams syndrome have elaborate and rich vocabularies and use very descriptive, affect-rich expressive language, which makes their speech very engaging," she says.
In terms of social behavior and language abilities, Williams syndrome is the opposite of autism. Individuals with autism are socially withdrawn and isolated. Many struggle to learn and use language effectively. Neuroscientists are studying the brains of individuals with both disorders in hopes of understanding not only the syndromes, but also the structure and development of the normal brain.
In a new study, researchers at the Salk Institute have measured and compared brainwave activity in people with both disorders (as compared to healthy controls). Not surprisingly, the scientists have found big differences. "[W]e found that the way the brain processes language mirrors the contrasting social phenotypes of Williams syndrome and autism spectrum disorders," says Salk neuropsychologist Inna Fishman.
Fishman and her team reached that conclusion after studying the distinct pattern of electrical activity in the brain called N400. N400 is part of the normal brain's response to words and other meaningful stimuli; it peaks about 400 milliseconds after the stimulus.
When presented with a typical sentence that finishes with an odd ending (for example, "I take my coffee with sugar and shoes"), individuals with Williams syndrome exhibit an abnormally large N400 response, indicating that they are particularly sensitive and attuned to semantic aspects of language. In contrast, individuals with autism spectrum disorders show a much smaller that normal N400 effect. These results indicate that people with autism may be less adept at getting the meaning of a word from its context.
"Our results suggest that language skills, or their brain correlates, go hand-in-hand with the level of sociability," Fishman says. In fact, Fishman and her colleagues have preliminary data that suggest an association between sociability and the magnitude of the N400 response among individuals with Williams syndrome. The Salk team is also working to correlate brainwave patterns with the genetic map of Williams syndrome. They want to find out how specific genes may produce the social behavioral and language characteristics of the syndrome.
For More Information:
There's a short and simple explanation of N400 peaks and processing here.
The research study will be published in a future issue of Social Cognitive and Affective Neuroscience.
Photo courtesy of the Salk Institute.