The Brain Can Forget an Invisible Hand

To be an expert is to know something like the back of your hand, or so the saying goes. But science suggests we don't know our own limbs quite as well as we think. For years scientists have used "rubber hand illusions" to show how the mind can be fooled: They cover a test subject's real hand with a towel, and then put a real-looking rubber hand in the place where it should be. After a while, the subjects' minds get the best of them and they "feel" sensations from the fake hand. In a new study [pdf, subscription required], Oxford University researchers went one step further and showed that the brain can begin to abandon a limb if it thinks it's got a replacement. Lorimer Moseley and colleagues put 11 volunteers through "rubber hand illusions" and measured the subjects' skin temperature. After 7 minutes the hidden hands had dropped about half a degree Fahrenheit, while the volunteer's body—and other real hand—remained at the same temperature. The more impact the person said the illusion had on them, the colder their hidden hand was. The scientists say that because the brain starts to feel like it owns the rubber hand, it starts to forget about the hidden hand. It's been a strange week for minds and hands: On Monday we wrote about Body Integrity Identity Disorder, the sufferers of which have an almost-irresistible urge to cut off one of their limbs. This new study is further evidence that you shouldn't take your relationship with your appendages for granted. Image: flickr/littledan77