The brain is bombarded by information about the physical proportions of our bodies. The most familiar sensations, such as a puff of wind or the brush of our own shirt sleeve, serve to constantly remind the brain of the body's outer bounds, creating a sense of what is known as proprioception. In a new study, researchers report this week that the brain's ability to interpret external signals and update its sense of bodily self is more dynamic than had been previously thought and that such updates can happen very quickly, altering within a matter of seconds how body parts and individual touch sensations are perceived.

The work is reported by researchers Frederique de Vignemont, Henrik Ehrsson, and Patrick Haggard at University College London.

The information that is integrated in the course of proprioception comes from several different senses, including touch, pain, vision, information from muscles, and so on. The brain must combine all these information inputs to accurately perceive the external world through our body's interaction with it and also to produce a coherent sense of self. Because all these signals carry such different kinds of information, the brain must perform a constant juggling act in order to make sense of the body and the world.

In the new study, the research team used a method called tendon vibration to induce a distortion of healthy volunteers' sense of their own bodies. When the biceps tendon of the right arm was vibrated, the subjects in the experiments felt within seconds that their right elbow was rotating away from the body, even though the arm was actually quite still. If subjects held their left index finger with their right hand while this happened, they felt their left index finger getting longer as they felt their arm move.

The team then tested how these bodily illusions rearranged the sense of touch. They touched subjects with two metal rods on the left index finger, and asked them to judge whether the d
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Contact: Heidi Hardman
hhardman@cell.com
1-617-397-2879
Cell Press
25-Jul-2005

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