UCL News


Honey, I've shrunk - but it's all in the mind

1 December 2005

Feeling fat or thin really is all in the mind, scientists have confirmed.

Researchers scanned the brains of volunteers who were given the sensation that their waists were shrinking. Each had a vibrating device placed on the wrist which created the illusion that the joint was flexing, even though it was not.

When the volunteer touched his or her waist it felt as if the wrist was bending into the body, giving an impression of getting thinner.

During the exercise, all 17 participants felt that their waist shrunk by up to 28%.

At the same time, their brains showed high levels of activity in a region called the posterior parietal cortex - an area that integrates sensory information from different parts of the body.

Volunteers who reported the strongest shrinking sensation also showed the strongest activity in this brain region.

Dr Henrik Ehrsson, who led the research at the University College London Institute of Neurology, said: "Other studies have shown that people with injuries in the parietal cortex area of the brain experience the feeling that the size and shape of their body parts have changed.

"People who suffer from migraine with aura can sometimes experience a phenomenon called the "Alice in Wonderland syndrome" where they feel that various body parts are shrinking. This could also be linked to the same region of the brain.

"In addition people with anorexia or body dysmorphic disorder who have problems judging the size of their body might similarly have a distorted representation of their body image in the parietal cortex." To process information about body size, the brain appeared to create a "map" bringing together signals from relevant body parts such as skin, joints and muscles, as well as visual cues.

John von Radowitz, PA Science, 29 November 2005