YOU may think you know the back of your hand like, well, the back of your hand. But scientists have found our brains contain distorted representations of the size and shape of our hands, with a tendency to think of them as shorter and fatter than they are.The work could have implications for how the brain unconsciously perceives other parts of the body and may help explain certain eating disorders in which body image becomes distorted.Neuroscientists at University College London asked more than 100 volunteers to place their left hand palm-down on a table. The researchers then covered the hands with a board and asked the volunteers to indicate where landmarks such as fingertips lay. This data was used to reconstruct the ”brain’s image” of the hand.The results, published in the Proceedings of the National Academy of Sciences, showed a consistent overestimation of the width of the hand, with many thinking their hand was about 80 per cent broader than it was. ”It’s a dramatic and highly consistent bias,” said Matthew Longo, from UCL’s Institute of Cognitive Neuroscience.The brain uses several ways to work out the location of different parts of the body, including feedback from muscles and joints and some sort of internal model of the size and shape of each part. ”Previously it has been assumed that the brain uses an accurate model of the body,” said Dr Longo. Instead,Dr Longo’s work shows that the brain’s models can be incorrect.Regions of high sensitivity in the skin, such as the fingertips and the lips, get a larger proportion of the brain’s territory. Dr Longo said this sensitivity was mirrored in the size of the fingers in the maps of perceived positions. ”You find the least underestimation for the thumb and more underestimation as you go across to the little finger.”He said the research showed how the brain’s ability to distort the body might underlie conditions such as anorexia nervosa.Guardian News & Media