In addition to Frank LeFever's suggestions, you might also look into:
F. Frank LeFever wrote:
>> We all share your dismay and resentment; this newsgroup has become an
> outlet for some bizarre and embarassing, undisciplined and
> self-indulgent or perhaps pathological thinking.
>> Some lines of research to look into:
>> "Phantom limb" studies.
>> "Chronic pain" or "central pain" studies.
>> I have paid someowhat more attention to the second line. There are
> some complex sequences of events, involving substance P, IL-1, NO,
> glutamate, and NMDA, by which peripheral stimuli can induce central
> changes (peripheral, i.e. nerves outside spinal cord; central, in the
> spinal cord or higher) which are long-lasting or perhaps permanent.
>> The glutamate/NMDA aspect is very similar to what in the brain is a
> route to LTP, a popular "model" of memory formation.
>> In one paradigm, a local irritation by formalin can produce changes
> such that there is a general (i.e. not local or regional) allodynia or
> abnormal sensitivity to painful stimuli.
>> F. Frank LeFever, Ph.D.
> New York Neuropsychology Group