How touching the face can elicit response in a 'phantom' limb'.

The patient does not have a left hand it has been amputated after an accident. Yet the patient still feels he has a hand: this is referred to as a 'phantom limb'.


The doctor approaches the patient's bed and commences his examination. He touches the patient’s body in different parts with a cotton swab, eliciting normal responses.


Then the doctor touches the patient’s face with the cotton swab and  this immediatly elicits sensations in the patient’s phantom hand.  

Throuhg this procedure medical reseach show that  an entire map of the absent hand is on the patient’s face.

But how is this? 

It is because the strip of cortex called the 'postcentral gyrus' the areas that deal with nerve inputs from the hand and face happen to be adjacent, so that in the case of amputation some sort of neighborly cross-activation occurs—the facial inputs spill over to the area that maps the phantom hand. So the idea of your hand is in your face.

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The fact that the representation of the face lies adjacent to the representation of the hand and arm in the cortical homunculus is crucial to explaining the origin of phantom limbs.