Objective and subjective measurement of pain: Current approaches for forensic applications

Pain, as with all conditions described in this volume, is a multidimensional experience (Melzack and Wall, 1965). The experience is described along two main axes: the sensory'discriminative dimension, comprising spatial, temporal, and intensity properties, and the affective'motivational dimension, related to the unpleasantness, behavioral, emotional, and social properties of the experience (Fernandez and Turk, 1992). Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or it is described in terms of such damage. Each individual learns the meaning of the word through experiences related to injury in early life (Merskey and Bogduk, 1994). This definition, now adopted by the International Association for the Study of Pain (IASP), recognizes that the experience of pain is measured as much by subjective thoughts, emotions, and behaviors as by objective measurement of anatomical, biological, or physiological pathology. As such, the experience of pain can never fully be confirmed or disconfirmed with absolute certainty by an external observer. However, the sequelae of pain, the resulting disability associated with pain, and the moderating perceptual, experiential, cognitive, and social factors can be assessed comprehensively, reliably, and validly to provide the professional with considerable information about the individual's experience of pain. This chapter will present a pragmatic framework for a comprehensive understanding of chronic pain. Three central questions should guide assessment of people with chronic pain: (1) What is the extent of the individual's disease or injury? (2) What is the magnitude of the illness?-that is, to what extent is the individual suffering, disabled, or unable to engage in activities? (3) Does the individual's behavior seem appropriate to the injury, evident pathology, or laboratory findings?-that is, are symptoms amplified or minimized for psychological or social reasons? We believe that in order to answer these questions, all of the perceptual and experiential dimensions of pain must be considered. The biopsychosocial model of chronic pain provides a multifactorial, heuristic model that depicts the various dimensions of pain experience. After presenting and describing the model, we review some of the most widely used and studied measures of pain that capture each dimension. Specific tools for measuring aspects of pain will be described with regard to the reliability and validity of each measure. We also focus on measures with predictive validity for chronicity and disability, believing that this aspect of validity is important to the readers of this volume. Finally, we consider future directions of research into functional brain mapping, as it might relate to objective measurement of brain areas underlying the experience of pain.