Brain Advance Access published online on March 2, 2009
Brain, doi:10.1093/brain/awn362
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Retinotopically defined primary visual cortex in Williams syndrome
1 Section on Integrative Neuroimaging, Clinical Brain Disorders Branch, National Institute of Mental Health, NIH, DHHS, Bethesda, MD, USA 2 Department of Psychological and Brain Sciences, University of Louisville, Louisville, KY, USA 3 Scientific and Statistical Computing Core, National Institute of Mental Health, Bethesda, MD, USA 4 Department of Paediatrics, University of Nevada School of Medicine, Las Vegas, NV, USA
Correspondence to:
Karen F. Berman, 10 Centre Drive, Rm 4C101, Bethesda, MD 20892-1365, USA E-mail: karen.berman{at}nih.gov
Williams syndrome, caused by a hemizygous microdeletion on chromosome 7q11.23, is characterized by severe impairment in visuospatial construction. To examine potential contributions of early visual processing to this cognitive problem, we functionally mapped the size and neuroanatomical variability of primary visual cortex (V1) in high-functioning adults with Williams syndrome and age- and IQ-matched control participants from the general population by using fMRI-based retinotopic mapping and cortical surface models generated from high-resolution structural MRI. Visual stimulation, consisting of rotating hemicircles and expanding rings, was used to retinotopically define early visual processing areas. V1 boundaries based on computed phase and field sign maps were used to calculate the functional area of V1. Neuroanatomical variability was assessed by computing overlap maps of V1 location for each group on standardized cortical surfaces, and non-parametric permutation test methods were used for statistical inference. V1 did not differ in size between groups, although its anatomical boundaries were more variable in the group with Williams syndrome. V1 overlap maps showed that the average centres of gravity for the two groups were similarly located near the fundus of the calcarine fissure, 
25 mm away from the most posterior aspect of the occipital lobe. In summary, our functional definition of V1 size and location indicates that recruitment of primary visual cortex is grossly normal in Williams syndrome, consistent with the notion that neural abnormalities underlying visuospatial construction arise at later stages in the visual processing hierarchy.
Key Words: Williams syndrome; retinotopy; V1; primary visual cortex; visuospatial construction
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Received May 16, 2008. Revised December 2, 2008. Accepted December 4, 2008.
*Present address: Central Institute of Mental Health, Mannheim, Germany.