Gernot S Doetsch GDOETSCH at mail.mcg.edu
Mon Jun 15 13:02:39 EST 1998

Gernot S Doetsch wrote:

>  <  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. >

The function of a sensory neuron depends on his input! When the main
input comes from the arm after hand amputation then it is an 'arm
neuron' now. But of cause this has nothing to do with perception.
Imaging, a higher neuron gets input form this neuron (that has now input
from the arm) and this higher neuron also gets some visual input, it
would be able to associate the visual input with the tactile input and
could learn, that the former 'hand neuron' now fires after tactile
stimulation of the arm.  The primary sensory neuron does not 'know'
where the input comes from. Neurons from higher - associative - areas
give a function to this. The point is, the higher areas are responsable
for the perception, the primary sensory neurons do the input selection.

<    I don't think there is any evidence that hand neurons switch their perceptual function to represent the arm -- which is the main issue.  Many years after amputation of the hand, stimulation of the arm or direct electrical stimulation of "deafferented hand neurons" still leads to sensation localized on the phantom hand.  The same is true following peripheral nerve lesions, neurovascular island transplants, spinal cord transection, etc.                        GSD                                                                 >

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