In a recent accident, your favorite uncle lost one of his arms just below the el

Your uncle still has the surviving parts of the sensory pathway that once served the entire arm. This may include the primary sensory neurons, since the severed axons could have regenerated (but even if these cells degenerated, the remainder of the pathway did not). Anything that stimulates the sensory nerve in the stump may cause signals to go to the area of the cerebral cortex that once received inputs only from the hand. Your uncle is not crazy, rather he is experiencing phantom limb pain, which is very real. This phenomenon illustrates labeled line coding and coding of stimulus location.

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