Gernot S Doetsch wrote:
> < 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 >
and Ed Ergenzinger wrote:
Yes, but do the higher order association areas learn that the input has
changed? If so, then why are there long-lasting phantom sensations? Why
don't all amputees go through a period of phantom sensation which
goes away after the higher order areas learn that the input is coming
a different portion of the body surface?
This is the open question.
The first hypothesis is, that there is no plasticity in higher areas
(but I can't believe it).
The other hypothesis could be, that the higher order neurons don't show
plasticity in these cases, because the change of their input (feedback
and feedforward and the coupling of both) is too weak. The input from
the primary neurons probably remains the same. The problem with amputees
is, that they don't use their arm instead of the amputated hand, they
use the other hand. So it is not the case, that the input from the arm
gets stronger - I would suppose it gets weaker because of disuse. So
there is not enough action to induce learning in higher areas.
What's about people who have amputated only one finger? If they
extensively use the other fingers of that hand, what's about phantom
perception and phantom pain in these persons? I don't know and it would
be very interesting to get some information about this point.
What one has to do is >active< training of the cortex to relearn a new
interpretation of the sensory inputs. Some people try to treat phantom
pain with tactile coactivation paradigms to make new associations. The
first results are very scattering but I believe it's the right way.
DR. BEN GODDE (Benjamin.Godde at neuroinformatik.ruhr-uni-bochum.de)
Institut f. Neuroinformatik, Ruhr-Universitaet, D-44780 Bochum
phone: + (0)234 7007975 fax: + (0)234 7094209