FoundationalConceptsNeuroscience

An analogous process can happen in humans. Sometimes as a
result of accident or disease a person may lose an arm or leg. Often in
these circumstances the person will continue to feel the presence of
the amputated limb, as if it were still there, a so-called phantom limb.
What is happening? In a person with an amputated arm, the region of
parietal lobe that normally receives signals from the arm is no longer
getting that input. As in the mouse with the amputated whisker, these
neurons do not sit idle but form connections with the neurons in
the adjacent regions of the body map. For the arm, this would be the
shoulder area and the face area. Thus, any somatosensory input that
activates neurons in these adjacent areas would also spill over and
activate neurons in the arm area. This is likely to explain the feeling
of a phantom arm. Any vague stimulation of the face and shoulder
of the amputee (air currents, temperature changes, and the like) also
activates neurons that would have once received signals from the now
missing arm. This neural activation might then be experienced as
coming from the missing arm. As a result of neuroplastic reorganiza-
tion of the body map, a phantom arm is born. If we could ask a mouse
with an amputated whisker to tell us about its experience, it would
perhaps report the feeling of a phantom whisker.