Oliver Sacks' Musicophelia: Phantom Fingers and the Case of the One-Armed Pianist

Reference
Oliver Sacks Musicophelia: Tales of Music and the Brain (2007)
Chapter 21: Phantom Fingers: The Case of the One-Armed Pianist

Summary
 This chapter of Oliver Sacks' Musicophelia deals with the issues of phantom limb syndrome.  In particular it looks at the experience of pianist Paul Wittgenstein, who lost his right arm during the first World War.  A former student of Wittgenstein's, Erna Otten, sent a letter to Sacks describing her lessons with Wittgenstein.  According to Otten, Wittgenstein described feeling every finger in his missing arm and would suggest fingerings to her while imagining his missing limb play. 
 Previously phantom-limbs were thought to be 'in the mind,' a purely psychic hallucinations.  The physician Silas Weir Mitchell first studied this during the Civil War.  Mitchell found that nearly all soldiers that he encountered with a missing limb experienced a phantom limb in the sense that they had sensations of that limb still being attached, in addition to a 'persistent neural representation of the limb in the brain' (p. 285).  They could describe willing a movement with their amputated arm with such precision and would often result in twitching in the remaining stump.  Mitchell showed that there were real neurological constructs dependent on the 'integrity of the brain, the spinal cord, and the remaining, proximal portions of the sensory and motor nerves in the limb' (p. 286). 
 More recent studies have found similar results.  A German study (Farsin Hamzei et al., 2001) found that the entire 'sensory-ideational-motor unit is activated in phantom motions' (p. 286).  Additionally, they found that there is a functional reorganization in the cortex following an amputation - the movements of the amputated limb are still represented in the cortex but also that the missing limb's representation is concentrated in the newly enlarged stump-area in the cortex. 
 In fact, this kind of willing of the nonexistent limb is essential to the successful use of a prosthesis.  It is the amplification of these nerve impulses that turns phantom movements into real ones.  Sacks muses on the philosophy of Paul Wittgenstein's brother, Ludwig Wittgenstein - perhaps, he suggests that the influence of his brother's experience can be seen in the the corporeality of his assertion 'If you do know that here is one hand, we'll grant you all the rest' (p. 289). 

Reflection
After reading this chapter, I am left wanting a fuller description of the experiential aspect of phantom-limb syndrome.  The first study posited that each soldier that had lost a limb experienced sensation in their missing limb - painful or otherwise  - but I am left wanting a fuller description.
As it relates to music, Sacks describes the process of choosing a fingering without a limb; one can certainly choose an appropriate fingering without feeling a limb, purely through imagining. However, I wonder if the imagining process differs for a person with a missing limb versus for a person with one that is in tact. The research that Sacks references seems to suggest that there is often a strong image of a missing limb, but that there is reorganization in the cortex - I would be interesting to see how such a reorganization affects one's perception of such activities as playing a musical instrument.   It would suggest that while one can still will the missing limb to move and imagine it, the 'functional reorganization of the cortex' would result in a different experience of one's body. 
Lastly, this question makes a strong case for 'mental practicing' to students - if Wittgenstein can effectively make musical and technical decisions without an arm, what excuse do we have?