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Science Frontiers ONLINE No. 123: May-Jun 1999 |
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Phantoms Of The Brain
In his review of a book with the above title (by V.S. Ramachandran and S. Blakeslee), D. Papineau repeats three irresistible anecdotes from the book. The people involved had either lost limbs or were partially paralyzed, so these three tales are at once sad, bizarre, and amusing.
The first two anecdotes involve amputees experiencing the phantom-limb phenomenon. The accepted explanation of this phenomenon is that the irritated stump of an amputee sends nerve messages that deceive the brain into signaling that the limb is there after all. Ramachandran, a neurologist, has shown that this theory is incorrect. Instead, he asserts, when the area of the brain assigned to the lost limb no longer receives sensory input from the area, it begins to react to sensory input arriving at adjoining areas in the brain. In other words, the idle area "overhears" nearby signals that are being processed and acts upon them in error.
This view explains why by simply stroking a man who had lost an arm, Ramachandran discovered two virtual hands in the man's face and shoulder. A touch on the man's cheek brought the response, "You're touching my thumb."
The second anecdote is explained by the fact that the area in the sensory cortex assigned to the genitals is located next to that for the feet. Genital stimulation of people who have lost a foot triggers sensations in the phantom leg. One man had orgasms in his phantom leg as well as his genitals!
Lastly, there are those people who cannot recognize that they are paralyzed, say, on their left sides. Even when they obviously fail to pick up things with their left arms and cannot tie their shoes, they are emphatic that they are not paralyzed. Strangely and inexplicably, squirting water in the left ear brings them back to reality, but only temporarily.
(Papineau, David; "Banishing the Ghosts," New Scientist, p. 43, September 26, 1998.)