The psychophysics of pain has an important role in the understanding of the neurophysiology of pain and for providing a scientific basis for modern methods of pain measurement and assessment. Psychophysical methods of sensory testing also have a pivotal role in understanding the mechanisms of pathophysiological pain wherein pain is an integral component of the disease itself and not merely a symptom. The main objective of this chapter is to explain how the combination of simple methods of direct scaling and sensory testing can be used to identify some of the mechanisms of pathophysiological pain. Indeed, this approach has long been anticipated in classical work on this subject (1). Psychophysical methods of direct scaling in combination with sensory tests of abnormal or enhanced pain mechanisms are useful in characterizing different types of persistent and intermittent pain conditions, including different types of neuropathic pain such as complex regional pain syndrome (CRPS), fibromyalgia pain, and irritable bowel syndrome (IBS) pain. In this chapter, we discuss human tests of pain responsiveness in patients with these conditions, with the aims of showing how such tests may be useful in characterizing hyperalgesia, allodynia, severity of pain states, and the mechanisms that serve them. This approach is likely to be useful in aiding diagnoses and ultimately matching treatments to pain syndromes.
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