INTRODUCTION. From results of our previous studies on motion and form coherence thresholds, and on a modification of the Goodale post box task, we have put forward a general hypothesis of ‘dorsal stream vulnerability’, where certain brain circuits, within the parietal and frontal lobes together with the cerebellum, develop differently to normal in Williams Syndrome (WS) children. Using comparative measures of motion and form coherence, we have extended this hypothesis to children with autism and focal lesions leading to hemiplegia and elucidated the brain networks using fMRI in normal adults. METHODS. We have tested both high functioning adults and young children with WS. We report results on two tasks: (a) an adaptation of the ‘altered views’ task of spatial reorientation — a virtual reality game to assess hippocampal function (adapted from O′ Keefe, Burgess and King); (b) Form and motion coherence thresholds in WS adults. RESULTS. In the altered views task, two inter-related difficulties have been identified for WS individuals: i) understanding the visual transformation from 2D to 3D; ii) the ability to switch between spatial representations at different positions in space (although spatial memory from a constant viewpoint may be normal). On coherence tasks we find that form coherence thresholds did not differ significantly between our groups of WS adults and normal controls, but motion coherence thresholds were significantly higher for the WS group. DISCUSSION. The results suggest that poor dorsal stream functioning in WS continues into adulthood, and that it is coupled to a difficulty in transforming environmental spatial information which may require hippocampal processing of visuospatial information. We discuss the broader ‘dorsal stream hypothesis’ in relation to other neurodevelopmental disorders such as perinatal brain injury.

Previous studies of children with Williams syndrome (WS) have found a specific deficit in dorsal cortical stream function, indicated by poor performance in coherence thresholds for motion compared to form. Here we investigated whether this is a transient developmental feature or a persisting aspect of cerebral organization in WS. Motion and form coherence thresholds were tested in a group of 45 WS individuals aged 16-42 years, and 19 normal adult controls.Although there was considerable variation in the coherence thresholds across individuals with WS, the WS group showed overall worse performance than controls. A significant group x threshold condition interaction showed a substantially greater performance deficit for motion than for form coherence in the WS group relative to controls. This result suggests that the motion deficit is an enduring feature in WS and is a marker for one aspect of dorsal-stream vulnerability. (c) 2005 Elsevier Ltd. All rights reserved.

Williams syndrome (WS) is a neurogenetic-neurodevelopmental disorder characterized by a highly variable and enigmatic profile of cognitive and behavioral features. Relative to overall intellect, affected individuals demonstrate disproportionately severe visual-spatial deficits and enhanced emotionality and face processing. In this study, high-resolution magnetic resonance imaging data were collected from 43 individuals with WS and 40 age- and gender-matched healthy controls. Given the distinct cognitive-behavioral dissociations associated with this disorder, we hypothesized that neuroanatomical integrity in WS would be diminished most in regions comprising the visual-spatial system and most "preserved" or even augmented in regions involved in emotion and face processing. Both volumetric analysis and voxel-based morphometry were used to provide convergent approaches for detecting the hypothesized WS neuroanatomical profile. After adjusting for overall brain volume, participants with WS showed reduced thalamic and occipital lobe gray matter volumes and reduced gray matter density in subcortical and cortical regions comprising the human visual-spatial system compared with controls. The WS group also showed disproportionate increases in volume and gray matter density in several areas known to participate in emotion and face processing, including the amygdala, orbital and medial prefrontal cortices, anterior cingulate, insular cortex, and superior temporal gyrus. These findings point to specific neuroanatomical correlates for the unique topography of cognitive and behavioral features associated with this disorder.

Objective: To investigate the discrete neural systems that underlie relatively preserved face processing skills in Williams syndrome (WS). Methods: The authors compared face and eye-gaze direction processing abilities in 11 clinically and genetically diagnosed WS subjects with 11 healthy age- and sex-matched controls, using functional MRI ( fMRI). Results: Compared to controls, WS subjects showed a strong trend toward being less accurate in determining the direction of gaze and had significantly longer response latencies. Significant increases in activation were observed in the right fusiform gyrus (FuG) and several frontal and temporal regions for the WS group. By comparison, controls showed activation in the bilateral FuG, occipital, and temporal lobes. Between-group analysis showed WS subjects to have more extensive activation in the right inferior, superior, and medial frontal gyri, anterior cingulate, and several subcortical regions encompassing the anterior thalamus and caudate. Conversely, controls had greater activation in the primary and secondary visual cortices. Conclusion: The observed patterns of activation in WS subjects suggest a preservation of neural functioning within frontal and temporal regions, presumably resulting from task difficulty or compensatory mechanisms. Persons with WS may possess impairments in visual cortical regions, possibly disrupting global-coherence and visuospatial aspects of face and gaze processing.