A comment on the Schmidt/Fordyce discussion

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In a recent discussion on ‘pain behavior’ and ‘pain ratings,’ held by Fordyce et al. and Schmidt (Pain, 33 (1988) 385-389), the latter introduces a pain dimension with on one extreme ‘pain behavior,’ and ‘nociception’ on the other. Furthermore, Schmidt adds a third concept: ‘pain perception’ of which he states that it: ‘ . . . takes a middle position on the pain dimension, relating to both pain behavior and nociception.’ The author also considers pain ratings, for example those obtained by the visual analog scale (VAS), a measure for pain perception. Later, Schmidt refers to this pain dimension as the 3-factor model of pain. He states: ‘I repeat: pain ratings are neither pain behaviors nor nociception but as an operationalization of pain perception have a distinct status on the pain dimension between nociception and pain behavior. This is called the 3-factor model of pain.’ This statement may lead to a conceptual confusion. First of all, a distinction needs to be made between pain constructs and the assessment method or instrument to quantify it. A pain rating is an instrument and cannot be placed on the same line with nociception and pain behaviors, which are constructs. The second, and more important, point is the erroneous introduction of the 3-factor model of pain, better known as the 3-systems model of pain. Schmidt refers to this model as if it presents a unidimensional representation of pain constructs, ranging from nociception to pain behavior, with pain perception in the middle. This is a clear misunderstanding of the model. The 3-systerns model of pain is in fact an application of the 3-systems model of emotion, first introduced by Lang [2] and Rachman [3], and widely applied to the area of anxiety research. According to this model, emotions are thought to be expressed by 3 different response systems: verbal report, overt motor responses, and expressive physiology. Emotions can, therefore, best be studied through these response systems, which should be considered as ‘a set of loosely coupled components.. . ,’ as they do not correlate [3]. The assumption is that emotions can be generated by 3 ‘channels’ which act partially independently from one another. Instead of a unidimensional conceptualization, a 3-dimensional one is suggested, an emotion being represented as a vector in a 3-dimensional space [6]. Although they acknowledged that some problems remain unresolved, Vlaeyen et al. [8] have argued in favor of the use of this model as a heuristic framework in chronic pain research, assessment, and treatment. Basically, their proposition is based on (1) the international recognition that pain is also an emotional experience [l], (2) the assumption that chronic pain might be considered a pathologic emotion [5], and (3) the observation that in the literature on chronic pain conceptualization, assessment and psychological treat-