title: Acquisition and extinction of somatic symptoms in response to odours: a Pavlovian paradigm relevant to multiple chemical sensitivity.
abstract: OBJECTIVE
  Multiple chemical sensitivity is a poorly understood syndrome in which various symptoms are triggered by chemically unrelated, but often odorous substances, at doses below those known to be harmful. This study focuses on the process of pavlovian acquisition and extinction of somatic symptoms triggered by odours.
  
  
  METHODS
  Diluted ammonia and butyric acid were odorous conditioned stimuli (CS). The unconditioned stimulus (US) was 7.4% CO2 enriched air. One odour (CS+) was presented together with the US for 2 minutes (CS+ trial), and the other odour (CS-) was presented with air (CS-trial). Three CS+ and three CS-exposures were run in a semi-randomised order; this as the acquisition (conditioning) phase. To test the effect of the conditioning, each subject then had one CS+ only--that is, CS+ without CO2--and one CS- test exposure. Next, half the subjects (n = 32) received five additional CS+ only exposures (extinction group), while the other half received five exposures to breathing air (wait group). Finally, all subjects got one CS+ only test exposure to test the effect of the extinction. Ventilatory responses were measured during and somatic symptoms after each exposure.
  
  
  RESULTS
  More symptoms were reported upon exposure to CS+ only than to CS-odours, regardless of the odour type. Altered respiratory rate was only found when ammonia was CS+. Five extinction trials were sufficient to reduce the level of acquired symptoms.
  
  
  CONCLUSIONS
  Subjects can acquire somatic symptoms and altered respiratory behaviour in response to harmless, but odorous chemical substances, if these odours have been associated with a physiological challenge that originally had caused these symptoms. The conditioned symptoms can subsequently be reduced in an extinction procedure. The study further supports the plausibility of a pavlovian conditioning hypothesis to explain the pathogenesis of MCS.
authors.affiliation: Department of Psychology, University of Leuven, Belgium.
authors.forename: O
authors.initials: O
authors.lastname: Van den Bergh
authors.forename: K
authors.initials: K
authors.lastname: Stegen
authors.forename: I
authors.initials: I
authors.lastname: Van Diest
authors.forename: C
authors.initials: C
authors.lastname: Raes
authors.forename: P
authors.initials: P
authors.lastname: Stulens
authors.forename: P
authors.initials: P
authors.lastname: Eelen
authors.forename: H
authors.initials: H
authors.lastname: Veulemans
authors.forename: K P
authors.initials: KP
authors.lastname: Van de Woestijne
authors.forename: B
authors.initials: B
authors.lastname: Nemery
mesh_terms: D000328:Adult; D000641:Ammonia; D000704:Analysis of Variance; D020148:Butyric Acid; D003214:Conditioning, Classical; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008297:Male; D018777:Multiple Chemical Sensitivity / Q000503:physiopathology / Q000523:psychology* / Q000628:therapy; D009812:Odorants; D011602:Psychophysiologic Disorders / Q000209:etiology* / Q000503:physiopathology / Q000628:therapy
chemical_list: D020148:Butyric Acid; D000641:Ammonia