Voxel-based morphometry

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Voxel based morphometry (VBM) is a neuroimaging analysis technique that allows investigation of focal differences in brain volume. It can be regarded as a form of so-called statistical parametric mapping. Traditionally, brain volume is measured by drawing regions of interest (ROIs) and calculating the volume enclosed. However, this is time consuming and can only provide measures of large areas. Smaller differences in volume may be overlooked. VBM registers every brain to a template, which gets rid of most of the large differences in brain anatomy among people. Then the brain images are smoothed so that each voxel represents the average of itself and its neighbors. Finally, volume is compared across brains at every voxel.

One of the first VBM studies and one that came to attention in main stream media was a study on the hippocampus brain structure of London taxi drivers^[1]. The VBM analysis showed the back part of the hippocampus was on average larger in the taxi drivers compared to control subjects while the frontal part was smaller. London taxi drivers need good spatial navigational skills and scientists have usually associated hippocampus with this particular skill.