Touch the face and feel the amputated hand...

This case study begins with a 43 year old woman who had her right arm amputated slightly above her elbow. She had phantom limb sensations and could move her both her phantom limb and phantom fingers. The limb was felt to move spatially in relation to her other non-amputated limb, and would move correctly when she walked. The only difference in feeling in the phantom limb from her other arm was that it felt colder. As a year progressed the phantom limb sensations started to fade. The fingers and hand were felt to move closer to the stump.

This is where it gets interesting. Cortical remapping occurs in response to an amputation. In phantom limb cases, this can cause cortical regions that represent the hand before amputation become responsive to stimuli from the facial region after the amputation. This seems to occur because the facial region is adjacent to the hand region in the motor cortex homunculus. This woman could feel her fingers and hand mapped out on the right side of her face. She has the sensation of someone touching her phantom hand at certain points when her face is touched.
A year after the first interview, the woman was interviewed again in a follow-up. The coritcal remapping that had first taken place the previous year had seemingly continued. The sensation of touching her hand when the right side of her face was touched had now also moved to the left side of her face! Now bilateral stimulation of her face could produce sensations in her phantom arm. The topographical map was different if the left side was touched than when the right side was touched. The thumb of the phantom hand was felt to be touched when any number of places on the face were stimulated. This was also true for the other fingers.

This was an interesting case due to the extent of the facial mapping of the the phantom limb. The outline below gives some further information.

The subject's phantom hand was represented on a topographic map of the facial region.
There was a time lag of about 5.6 seconds between touching the left side of the face and the subsequent feeling in the hand.
The time lag was only 1.8 seconds when the right side of the face was stimulated.
The feeling of the phantom limb being touched was more vivid when the left side of the face was stimulated than with the right side.
When the subject's pinkie was moved passively, there was subsequent synchrony of movement in the phantom pinkie.
There was no sensation in the non-amputated hand when the face was stimulated. (Halligan et. al)

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