When you brush your teeth, the toothbrush may actually become part of your arm – at least as far as your brain is concerned. That's the conclusion of a study showing perceptions of arm length change after people handle a mechanical tool.
The brain maintains a physical map of the body, with different areas in charge of different body parts. Researchers have suggested that when we use tools, our brains incorporate them into this map.
To test the idea, Alessandro Farné of the University of Claude Bernard in Lyon, France, and colleagues attached a mechanical grabber to the arms of 14 volunteers. The modified subjects then used the grabber to pick up out-of-reach objects.
Shortly afterwards, the volunteers perceived touches on their elbow and fingertip as further apart than they really were, and took longer to point to or grasp objects with their hand than prior to using the tool.
The explanation, say the team, is that their brains had adjusted the brain areas that normally control the arm to account for the tool and not yet adjusted back to normal.
"This is the first evidence that tool use alters the body [map]," says Farné.
Farné says the same kind of brain "plasticity" might be involved in regaining control of a transplanted hand or a prosthetic limb when the original has been lost. The brain might also readily incorporate cyborg additions – a cyborg arm or other body part – into its body schema, says Farné, "and possibly new body parts differing in shape and/or number, for example four arms."
Small implants such as pacemakers are inserted in the existing body so do not need to be accepted by the body schema, adds Farné, "but a pair of wings would – that would be tough!"
