Scientists have identified the region of the brain that is responsible for the way people view their bodies. The parietal cortex generates the body image, and disruption of the region's normal functioning could play a role in conditions such as anorexia and body dysmorphic disorder, in which people grossly over- or underestimate their body size, researchers believe.

The researchers, led by Henrik Ehrsson, a neuroscientist at University College London, scanned volunteers' brains while carrying out an illusion that made them think their waists were shrinking.

Each of the 17 volunteers had a vibrating device attached to their wrist to stimulate a tendon, which created the false sensation that the wrist joint was flexing. When they placed their hand on any part of the body, the imaginary wrist movement made them think that part of the body was shrinking or growing.

"This technique is known as the Pinocchio illusion because you feel as if your nose is getting longer when you grab the tip of your nose. It is a way to trick the brain and manipulate the body image," said Dr Ehrsson.

He asked the volunteers to close their eyes and put a hand on their waist. Immediately they felt as if the waist was shrinking by more than a quarter of its original size. At the same time the scientists used a brain scanning technique known as functional magnetic resonance imaging to measure changes in the blood flow in the brain.

"We found that a specific part of the parietal cortex was very active during the experiment," said Dr Ehrsson, whose study appears in the online journal Public Library of Science Biology. Volunteers who felt the strongest shrinking sensation showed the highest activity in this area of the brain. "It supports the idea that our brains compute our body size by integrating signals from the skin, muscles and joints, as well as visual cues," he said.

Other studies have shown that damage to the parietal cortex can make people feel their shape has 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," said Dr Ehrsson.

The scientists believe that an over- or underactive parietal cortex may be partly responsible for conditions such as anorexia and body dysmorphic disorder.

They now hope to repeat their experiment on people with those conditions to see if activity in the brain region differs from those without the condition. They also hope to experiment by stimulating this area of the brain in healthy subjects to manipulate how fat or thin people feel, potentially leading to a way of treating disorders such as anorexia.