Individuals with Williams syndrome, a genetic developmental condition that causes deficits in visuospatial processing but enhanced emotionality and face processing, have decreases and increases in relative cortical volume that parallel these abnormalities.

In a study published in The Journal of Neuroscience, Reiss and colleagues used a combination of volumetric analysis and voxel-based morphometry to compare the brains of people with Williams syndrome and those of control subjects. Williams syndrome causes various cognitive and behavioural abnormalities, including mild to moderate intellectual deficits, but visuospatial processing is disproportionately affected. The authors hypothesized that the parts of the cortex that make up the 'dorsal stream', which is responsible for visuospatial processing, might be abnormally small in affected individuals. They also looked for changes in parts of the brain that are involved in emotion and face processing, as people with the syndrome show increased emotional behaviour and are relatively good at face processing.

Overall, the study found that patients with Williams syndrome had an 11% reduction in cerebral volume. However, the thalamus, occipital cortex and other areas that are involved in visuospatial processing had greater decreases in grey matter volume, consistent with the pronounced deficits seen in these individuals. When the authors looked at areas involved with emotional processing and behaviour — including the amygdala, orbital and medial prefrontal cortex and anterior cingulate cortex — they found that these areas were relatively larger than normal.

It is not unusual for damage or grey matter loss in a particular brain area to cause deficits in a specific aspect of cognition, perception or behaviour. But it is much rarer to find the opposite situation — a relative increase in volume in a part of the brain causing an enhancement in function. Now, the challenge for researchers is to discover how a deletion on one copy of chromosome 7 can produce such a striking and characteristic pattern of anatomical changes. If we can find the answer to this question, it must surely also shed new light on the normal development of the cortical networks that process visuospatial and emotional information.