title: Short-term olfactory sensitization involves brain networks relevant for pain, and indicates chemical intolerance.
abstract: Chemical intolerance is a medically unexplained affliction that implies deleterious reactions to non-toxic everyday chemical exposure. Sensitization (i.e. increased reactivity to repeated, invariant stimulation) to odorous stimulation is an important component in theoretical explanations of chemical intolerance, but empirical evidence is scarce. We hypothesized that (1) individuals who sensitize to repeated olfactory stimulation, compared with those who habituate, would express a lower blood oxygenated level dependent (BOLD) response in key inhibitory areas such as the rACC, and higher signal in pain/saliency detection regions, as well as primary and/or secondary olfactory projection areas; and (2) olfactory sensitization, compared with habituation, would be associated with greater self-reported chemical intolerance. Moreover, we assessed whether olfactory sensitization was paralleled by comparable trigeminal processing - in terms of perceptual ratings and BOLD responses. We grouped women from a previous functional magnetic imaging study based on intensity ratings of repeated amyl acetate exposure over time. Fourteen women sensitized to the exposure, 15 habituated, and 20 were considered "intermediate" (i.e. neither sensitizers nor habituaters). Olfactory sensitizers, compared with habituaters, displayed a BOLD-pattern in line with the hypothesis, and reported greater problems with odours in everyday life. They also expressed greater reactions to CO2in terms of both perceived intensity and BOLD signal. The similarities with pain are discussed.
authors.affiliation: Department of Psychology, Umeå University, Umeå, Sweden; Department of Occupational and Public Health Sciences, University of Gävle, Sweden. Electronic address: linus.andersson@umu.se.
authors.forename: Linus
authors.initials: L
authors.lastname: Andersson
authors.affiliation: Department of Psychology, Umeå University, Umeå, Sweden. Electronic address: anna-sara.claeson@umu.se.
authors.forename: Anna-Sara
authors.initials: AS
authors.lastname: Claeson
authors.affiliation: Department of Integrative Medical Biology and Physiology, Umeå University, Umeå, Sweden; Department of Radiation Sciences, Umeå University, Umeå, Sweden. Electronic address: lars.nyberg@umu.se.
authors.forename: Lars
authors.initials: L
authors.lastname: Nyberg
authors.affiliation: Department of Psychology, Umeå University, Umeå, Sweden. Electronic address: steven.nordin@umu.se.
authors.forename: Steven
authors.initials: S
authors.lastname: Nordin
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000000981:diagnostic imaging / Q000502:physiology*; D002245:Carbon Dioxide / Q000494:pharmacology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009812:Odorants; D010146:Pain / Q000000981:diagnostic imaging / Q000503:physiopathology*; D000439:Pentanols / Q000494:pharmacology; D012903:Smell
chemical_list: D000439:Pentanols; D002245:Carbon Dioxide; C005716:amyl acetate
keywords: Chemical intolerance; Olfactory; Sensitization; Smell; Trigeminal; fMRI