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Imagine being attacked by one of your own hands, which repeatedly tries to slap and punch you. Or you go into a shop and when you try to turn right, one of your legs decides it wants to go left, leaving you walking round in circles.
Last summer I met 55-year-old Karen Byrne in New Jersey, who suffers from Alien Hand Syndrome.
Her left hand, and occasionally her left leg, behaves as if it were under the control of an alien intelligence.
Karen’s condition is fascinating, not just because it is so strange but because it tells us something surprising about how our own brains work.
Karen’s problem was caused by a power struggle going on inside her head. A normal brain consists of two hemispheres which communicate with each other via the corpus callosum.
The left hemisphere, which controls the right arm and leg, tends to be where language skills reside. The right hemisphere, which controls the left arm and leg, is largely responsible for spatial awareness and recognising patterns.
Usually the more analytical left hemisphere dominates, having the final say in the actions we perform.
The discovery of hemispherical dominance has its roots in the 1940s, when surgeons first decided to treat epilepsy by cutting the corpus callosum. After they had recovered, the patients appeared normal. But in psychology circles they became legends.
That is because these patients would, in time, reveal something that to me is truly astonishing - the two halves of our brains each contain a kind of separate consciousness. Each hemisphere is capable of its own independent will.
photo { Chris McPherson }
