Question

Months after the accident, your amputee uncle's phantom limb pain subsides. One afternoon he is sleeping and you see a fly walk across his upper lip. He wakes up and tells you he just had the funniest feeling. It was as if someone was touching his missing index finger. You decide to experiment with your uncle and you blindfold him. As you touch his cheek he tells you that you are touching his cheek and his missing thumb! As you move around his face you map out his fingers and forearm on his face. Hypothesize how this could be possible.

Answer 1

A phantom limb is the sensation that an amputated or missing limb is still attached. Approximately 80 to 100% of individuals with an amputation experience phantom sensations in their amputated limb.

This phantom limb phenomenon has been found to be caused by the changes occurring in the cortex of the brain following amputation of a limb. It has been found that the brain continues to receive signals from the nerve endings that originally supplied signals to and from the missing limb. It is also thought to be caused by the brain rewiring itself and rearranging sensory information to adjust to the changes in the body.

Later the patient devoloped a sensation of touch in the missing fingers during touch on the face this phenominon is due to Hand to face remapping.

A few weeks after amputation of an arm, sensory stimuli applied to the ipsilateral face are experienced by the patient as arising from the missing (phantom) arm. There is often a highly specific topographically organized map of the hand on the face with clearly delineated digits.

This referral of sensations is possibly caused by reorganization of somatosensory maps in the brain . The entire right side of the body is mapped onto the postcentral gyrus of the left hemisphere, known since Penfield, and the map is systematic except for the face being directly below the hand rather than near the neck. After arm amputation the sensory input from the face, which normally projects only to the face area, now “invades” the vacated territory corresponding to the denervated hand territory. As a result, stimuli applied to the face now activate the hand region of the brain and are therefore interpreted by higher brain centers as arising from the missing phantom hand (the remapping hypothesis).