Research: Sizing things up

25 January 2006

Our brains perceive body size by combining signals from different body areas.

Unlike touch and pain, there are no specialised areas for body size in the brain. Instead it is thought that body size is calculated relative to other objects in the environment, through sensory input from different parts of the body.

Dr Henrik Ehrsson and colleagues from the Wellcome Department of Imaging Neuroscience at UCL and other centres set out to unravel how the brain perceives changes in the size and shape of our bodies.

Since bodies do not normally change in size very quickly, the researchers took advantage of a perceptual illusion known as the 'Pinocchio illusion', which made subjects feel that their waists were shrinking. The team then used functional magnetic resonance imaging to see what was happening in their brains.

The illusion triggered activity in a part of the brain called the parietal cortex, which may be processing signals from different body parts to produce a sense of body size.

External links

• Ehrsson HH et al. Neural substrate of body size: illusory feeling of shrinking of the waist. PLoS Biol 2005;3(12):e412.