July 12, 2007

Williams Syndrome

In the July 8 New York Times Sunday Magazine, David Dobbs reviews aspects of Williams Syndrome in "The Gregarious Brain". As others have done, he uses Williams syndrome as a springboard to discuss the genetics of personality, neuroscience, and even the evolution of language.

Williams Syndrome brains are on average 15% smaller than normal. A disproportionate amount of this discrepancy is accounted for by smaller dorsal regions. Ventral regions are denser in synaptic connections. Their affability has in part been linked to their lack of connection between the orbitofrontal cortices and amygdylae when interpreting menacing faces. Therefore they know no social fear.

The link between language and sociability, which Williams seems to demonstrate, provides support for the social-brain theory. It states that human neocortex increased to deal with larger social groups. Across primate species the size of the neocortex correlates with the size of the social group. In this theory language was a neocortical adaptation that allowed the maintenance of a large social network without physical grooming; instead relationships could be cultivated with verbal grooming.

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