Distorted Symptom Perception in Patients With Medically Unexplained Symptoms Katleen Bogaerts, Lien Van Eylen, Wan Li, Johan Bresseleers, Ilse Van Diest, and Steven De Peuter University of Leuven Linda Stans and Marc Decramer University Hospital Gasthuisberg Omer Van den Bergh University of Leuven The present study investigated differences in symptom perception between a clinical sample with medically unexplained symptoms (MUS) and a matched healthy control group. Participants (N = 58, 29 patients) were told that they would inhale different gas mixtures that might induce symptoms. Next, they went through 2 subsequent rebreathing trials consisting of a baseline (60 s room air breathing), a rebreathing phase (150 s, which gradually increased ventilation, PCO 2 in the blood, and perceived dyspnea), and a recovery phase (150 s, returning to room air breathing). Breathing behavior was continuously monitored, and dyspnea was rated every 10 s. The within-subject correlations between dyspnea on the one hand and end-tidal CO 2 and minute ventilation on the other were used to index the degree to which perceived dyspnea was related to specific relevant respiratory changes. The results showed that perceived symptoms were less strongly related to relevant physiological parameters in MUS patients than in healthy persons, specifically when afferent physiological input was relatively weak. This suggests a stronger role for top-down psychological processes in the symptom perception of patients with MUS. Keywords: medically unexplained symptoms, symptom perception, schema, dyspnea, rebreathing test Medically unexplained symptoms (MUS), or bodily symptoms in the absence of an organic disease or physiological dysfunction, are a widespread problem in modern society. Twenty-five to 50% of primary care patients present with MUS (Burton, 2003; Katon, Ries, & Kleinman, 1984; Kroenke, 2003), making it the most common category of complaints in general medical practice (Kir- mayer & Taillefer, 1997). In secondary care, prevalence rates are even higher (Nimnuan, Hotopf, & Wessely, 2001). The high prevalence of MUS constitutes a major theoretical, clinical, and socioeconomical challenge (Nimnuan, Hotopf, & Wessely, 2000). Interestingly, reporters of MUS are commonly marked by high negative affectivity (NA). Trait NA is a mood-related disposition to experience negative emotions. A robust association of trait NA with enhanced symptom reports has been widely accepted in the literature (for an overview, see Van Diest et al., 2005). Several theoretical accounts of the underlying mechanisms of MUS have been advanced (Rief & Barsky, 2005). The present study takes a symptom perception perspective. The central as- sumption of all accounts using this perspective is that there is no simple one-on-one correspondence between peripheral physiolog- ical changes and the perception of physical symptoms (see Rief & Broadbent, 2007, for a review). Symptoms are not the direct result of the passive registration of bodily changes but are modulated by “top-down” cognitive processes. A selection mechanism is hypoth- esized to play a role in the processing of somatic information so that only a small proportion of it reaches the level of conscious- ness. It serves a survival value that only motivationally important somatic information warns the conscious brain to take action in order to restore homeostatic balance (Craig, 2002) and that low- intensity and/or irrelevant somatic information is filtered out and kept below the perception threshold. This allows an optimal bal- ance between caring for the internal homeostasis and keeping resources available to respond appropriately to changing external demands in the environment. The selection process is guided by information in memory: Schematic information, conceived of as the record of a personal learning history with somatic experiences— including related beliefs, expectations, and negative affective connotations—may influence the perception and appraisal of the bodily condition (Brown, 2004; Van den Bergh, Stegen & Van de Woestijne, 1997, 1998). It is therefore important to distinguish between (interoceptive) sensations and symptoms, terms that are often used interchangeably in the literature. An interoceptive sen- sation refers to a sensory process related to perceiving information from within the body, whereas a symptom refers to the experience of such information in a negative manner. While the term sensa- Katleen Bogaerts, Lien Van Eylen, Wan Li, Johan Bresseleers, Ilse Van Diest, Steven De Peuter, and Omer Van den Bergh, Department of Psy- chology, University of Leuven; Linda Stans and Marc Decramer, Univer- sity Hospital Gasthuisberg, Leuven, Belgium. Katleen Bogaerts is a postdoctoral fellow of the Research Foundation– Flanders (FWO). Correspondence concerning this article should be addressed to Katleen Bogaerts, Research Group on Health Psychology, Department of Psychol- ogy, University of Leuven, Tiensestraat 102, B-3000, Leuven, Belgium. E-mail: katleen.bogaerts@psy.kuleuven.be Journal of Abnormal Psychology © 2010 American Psychological Association 2010, Vol. 119, No. 1, 226 –234 0021-843X/10/$12.00 DOI: 10.1037/a0017780 226