If I don't misunderstand You, You say that a "hand neuron", representing
the arm after hand amputation remains a "(phantom) hand neuron", because
the higher cortical neurons "looking" on this primary sensory neuron
have learned so. Well, then the question would be, if these higher
cortical areas also have a plastic capability and how to tell these
neurones to re-learn their input. So far as I know, there are no studies
on plasticity in higher cortical areas and it could be the big challenge
for the next decade.
< The point is that the "hand neurons" do not "represent " the arm -- these neurons receive new input from the arm but, when activated, still "represent" the hand. That's why stimulation of the arm is referred to the phantom hand. Higher centers don't have to learn anything in this case. >
Braille readers and string instrument players have enlarged finger
representations. This means, that neurons not responding to finger
stimulation at birth do so after some months or years of training. So I
would say, they have moved their function from not-finger to finger
representation and processing.
< Yes, learning is different from denervation. In this case, extensive training could increase the task-specific, finger responses of a population of neurons AND recruit surrounding, normally subthreshold, neurons into the responding population, hence increasing the size of the cortical finger area. However, there is no clear evidence that the function of the recruited neurons has changed from one thing to another. GSD >