title: Brain responses to olfactory and trigeminal exposure in idiopathic environmental illness (IEI) attributed to smells -- an fMRI study.
abstract: OBJECTIVE
  Idiopathic environmental intolerance (IEI) to smells is a prevalent medically unexplained illness. Sufferers attribute severe symptoms to low doses of non-toxic chemicals. Despite the label, IEI is not characterized by acute chemical senses. Theoretical models suggest that sensitized responses in the limbic system of the brain constitute an important mechanism behind the symptoms. The aim was to investigate whether and how brain reactions to low-levels of olfactory and trigeminal stimuli differ in individuals with and without IEI.
  
  
  METHODS
  Brain responses to intranasally delivered isoamyl acetate and carbon dioxide were assessed in 25 women with IEI and 26 non-ill controls using functional magnetic resonance imaging.
  
  
  RESULTS
  The IEI group had higher blood-oxygenated-level-dependent (BOLD) signal than controls in the thalamus and a number of, mainly, parietal areas, and lower BOLD signal in the superior frontal gyrus. The IEI group did not rate the exposures as more intense than the control group did, and there were no BOLD signal differences between groups in the piriform cortex or olfactory regions of the orbitofrontal cortex.
  
  
  CONCLUSIONS
  The IEI reactions were not characterized by hyper-responsiveness in sensory areas. The results can be interpreted as a limbic hyperreactivity and speculatively as an inability to inhibit salient external stimuli.
authors.affiliation: Department of Psychology, Umeå University, Sweden. Electronic address: linus.andersson@psy.umu.se.
authors.forename: Linus
authors.initials: L
authors.lastname: Andersson
authors.affiliation: Department of Psychology, Umeå University, Sweden.
authors.forename: Anna-Sara
authors.initials: AS
authors.lastname: Claeson
authors.affiliation: Department of Integrative Medical Biology and Physiology, Umeå University, Sweden; Department of Radiation sciences, Umeå University, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Nyberg
authors.affiliation: Department of Public Health and Clinical Medicine, Umeå University, Sweden.
authors.forename: Berndt
authors.initials: B
authors.lastname: Stenberg
authors.affiliation: Department of Psychology, Umeå University, Sweden.
authors.forename: Steven
authors.initials: S
authors.lastname: Nordin
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D002245:Carbon Dioxide; D018876:Environmental Illness / Q000175:diagnosis / Q000503:physiopathology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D018777:Multiple Chemical Sensitivity / Q000175:diagnosis* / Q000503:physiopathology*; D009812:Odorants; D009832:Olfactory Nerve / Q000503:physiopathology*; D010296:Parietal Lobe / Q000503:physiopathology; D000439:Pentanols; D017397:Prefrontal Cortex / Q000503:physiopathology; D013788:Thalamus / Q000503:physiopathology; D014276:Trigeminal Nerve / Q000503:physiopathology*
chemical_list: D000439:Pentanols; D002245:Carbon Dioxide; C020377:isoamyl acetate
keywords: Chemical intolerance; Idiopathic environmental intolerance; Multiple chemical sensitivity; Olfactory; Trigeminal; fMRI