inhibiting pathways, and secure considerable periods of relief (Young et al., 1984). Relief has 
also been achieved for a different, much more frequently encountered group of pain patients, 
in whom the physical cause of the pain cannot be determined. This includes many patients 
with longstanding back pain. Treatments using principles of reinforcement and extinction, 
originally derived from experiments on animals, have eliminated these patients' dependence 
on narcotics and have restored many to normal activities (Fordyce et al., 1973; Roberts and 
Reinhardt, 1980). 
Recent developments in the area of pain research use animal models of persistent pain that 
mimic inflammatory and neuropathic pain conditions in humans. In these conditions, stimuli 
that normally are not painful are perceived as painful. The severe pain that an arthritic 
patient experiences when fingers are moved is just one example. The animal models of these 
conditions have contributed greatly to our understanding of chronic pain and the development 
of new methods for controlling chronic pain (Casey and Dubner, 1989; Walker et al., 1999). 
Of great interest is a new appreciation that persistent pain conditions are not just a 
prolongation of acute pain processing, but rather result from changes in properties of the 
nervous system. These changes, which include the induction of new genes and the synthesis 
of new molecules, enhance pain processing, such that signals that normally are not painful 
become painful and persist (Basbaum and Woolf, 1999). Current development of 
pharmacological agents directed at the molecules that underlie these chronic pain-induced 
changes should significantly improve the treatment of pain in the near future. 
PSYCHOTHERAPY 
Previous to work by Dollard and Miller (1950), the psychosocial treatment of choice for non- 
psychotic disturbances consisted primarily of psychoanalysis practiced almost exclusively by 
medical professionals (McHugh, 2000). Dollard and Miller (1950) used the principles of 
learning derived from animal experiments as well as animal work on fear and displacement 
behavior to demonstrate that neuroses are learned and that psychotherapy could be 
considered a process in which the individual learns more adaptive social and emotional- 
habits. The perception of psychotherapy as a learning process, following scientifically 
established principles of conditioning, positive and negative reinforcement, extinction, and so 
on, made its practice more accessible, both to practitioner and to prospective patient. More 
psychologists, as well as medical doctors thereafter, undertook the practice of psychotherapy. 
Today, practice is extended to various other help professionals, thus extending the supply of 
practitioners to meet the growing demand for services by an ever-broadening patient 
population. 
Wolpe (1958) introduced a new therapeutic technique, systematic desensitization, based on 
the principles of learning theory. This technique used principles of reinforcement, counter 
conditioning, experimental extinction, and stimulus generalization derived from experiments 
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