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.
It started after Karen had surgery at 27 to control her epilepsy, which had dominated her life since she was 10. Surgery to cure epilepsy usually involves identifying and then cutting out a small section of the brain, where the abnormal electrical signals originate.
When this does not work, or when the damaged area cannot be identified, patients may be offered something more radical. In Karen’s case her surgeon cut her corpus callosum, a band of nervous fibres which keeps the two halves of the brain in constant contact.
Cutting the corpus callosum cured Karen’s epilepsy, but left her with a completely different problem. Karen told me that initially everything seemed to be fine. Then her doctors noticed some extremely odd behaviour.
“Dr O’Connor said ‘Karen what are you doing? Your hand’s undressing you’. Until he said that I had no idea that my left hand was opening up the buttons of my shirt.
“So I start rebuttoning with the right hand and, as soon as I stopped, the left hand started unbuttoning them. So he put an emergency call through to one of the other doctors and said, ‘Mike you’ve got to get here right away, we’ve got a problem’.”…
[continues at BBC News]