Generalization of acquired somatic symptoms in response to odors: A pavlovian perspective on multiple chemical sensitivity

Objective: Somatic symptoms that occur in response to odors can be acquired in a pavlovian conditioning paradigm. The present study investigated 1) wh ether learned symptoms can generalize to new odors, 2) whether the generali zation gradient is linked to the affective or irritant quality of the new o dors, and 3) whether the delay between acquisition and testing modulates ge neralization. Methods: Conditional odor stimuli (CS) were (diluted) ammonia and niaouli. One odor was mixed with 7.4% CO2-enriched air (unconditional stimulus) during 2-minute breathing trials (CS+ trial), and the other odor was presented with air (CS-trial). Three CS+ and three CS+ trials were cond ucted in a semirandomized order (acquisition phase). The test phase involve d one CS+-only (CS+ without CO2) and one CS-test trial, followed by three t rials using new odors (butyric acid, acetic acid, and citric aroma). Half o f the subjects (N = 28) were tested immediately, and the other half were te sted after 1 week. Ventilatory responses were measured during and somatic s ymptoms were measured after each trial. Results: Participants had more symp toms in response to CS+-only exposures, but only when ammonia was used as t he CS+. Also, generalization occurred: More symptoms were reported in respo nse to butyric and acetic acid than to citric aroma and only in participant s who had been conditioned. Both the selective conditioning and the general ization effect were mediated by negative affectivity of the participants. T he delay between the acquisition and test phases had no effect. Conclusions : Symptoms that occur in response to odorous substances can be learned and generalize to new substances, especially in persons with high negative affe ctivity. The findings further support the plausibility of a pavlovian persp ective of multiple chemical sensitivity.