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Sick of smells : Empirical findings and a theoretical framework for chemical intolerance
2012 (English)Doktorsavhandling, sammanläggning (Other academic)
Abstract [en]

Chemical intolerance (CI) is a term that refers to the surprisingly common phenomenon of persons getting ill from everyday chemicals. Although seemingly similar to asthma and allergies, CI sufferers do not react to exposures with increased histamine release. CI neither conforms to toxicological dose-response relationships as sufferers react to very low concentrations of chemicals assumed to be harmless. In addition, no particular chemical can be tied to any particular set of symptoms as in the case of other kinds of toxic injuries. The two overreaching goals of this thesis were to empirically investigate important hypotheses regarding CI, and to develop a theoretical framework that integrates previous theories of CI into a coherent whole.There are four empirical studies in this thesis. Utilizing event-related potentials (ERPs), magnitude estimations of perceived intensity, detection tests and functional magnetic resonance imaging (fMRI), the studies provided support for the following hypotheses: (1) persons with self-reported CI sensitize to olfactory and chemosomatosensory stimuli, whereas non-intolerant individuals habituate; (2) sensitization in CI is similar in terms of brain activation patterns to both non-clinical sensitization and other unexplained illnesses such as fibromyalgia; (3) persons with CI have an attention bias to chemical exposures, reflected by problems with withdrawing attention from such stimuli; (4) measures of peripheral hyperreactivity are correlated with chemosensory ERP measures; but failed to corroborate (5) the reactions of women resemble those found in persons with CI to a greater degree than the case in men.Three major theories of CI are also discussed. The neural sensitization theory describes CI as pathological and non-immunological increases in neural responsiveness. The conditioning theory describes CI as the result of basic associative learning mechanisms. The neurogenic inflammation theory describes CI as proliferation of sensory c-fibers and inflammatory responses carried to several parts of the body through axon reflexes and release of inflammatory mediators. The main point of the theoretical synthesis is that the theories offer different and complementary perspectives on CI, rather than presenting conflicting ontologies. With an integrated perspective, infected debates whether CI is a psychological or organic illness can hopefully be avoided.Finally, the unexplained characteristics of CI, the empirical findings and the theoretical accounts are described within the theoretical framework of signal detection theory. Several features of CI, e.g. sensitization and peripheral hyperreactivity, are described in terms of applying a low criterion (ß).

Abstract [sv]

Kemisk intolerans, det vill säga att få symtom av vardagliga lukter, är ett förvånansvärt vanligt problem. Trots att åkomman i många avseenden liknar astma och allergi, reagerar de drabbade inte med exempelvis ökad histaminfrisättning. Kemisk intolerans överensstämmer inte heller med toxikologiska dos-responsförhållanden, eftersom de drabbade blir sjuka av väldigt låga koncentrationer av luktämnen. Enskilda kemikalier kan inte kopplas till en karaktäristisk symtombild, vilket är vanligt vid andra typer av toxikologiska skador. I denna avhandling har jag två mål. För det första undersöker jag viktiga hypoteser om kemisk intolerans. För det andra erbjuder jag ett teoretiskt ramverk där jag integrerar tidigare teorier om kemisk intolerans till en sammanhängande helhet.Den empiriska delen av avhandlingen består av fyra forskningsstudier. Baserat på händelserelaterade hjärnpotentialer (ERPs), magnitudestimationer av upplevd styrka, detektionstest samt funktionell magnetresonansavbildning (fMRI) stöder studierna följande hypoteser: (1) personer med självrapporterad kemisk intolerans sensitiserar till olfaktoriska och kemosomatosensoriska stimuli, medan icke-intoleranta individer habituerar; (2) med avseende på hjärnaktiveringsmönster liknar sensitisering hos kemiskt intoleranta det mönster man finner både i icke-klinisk sensitisering och i exempelvis fibromyalgi; (3) personer med kemisk intolerans har en benägenhet att uppmärksamma kemisk exponering, vilket reflekteras i en oförmåga att ignorera sådana stimuli; (4) mått på perifer hyperreaktivitet korrelerar med kemosensoriska ERP-mått. Hypotesen att (5) kvinnors reaktioner på kemosensoriska stimuli liknar de man kan finna hos de kemiskt intoleranta i större utsträckning än vad fallet är för män, stöds däremot inte.Tre teorier om kemisk intolerans diskuteras. Den neurala sensitiseringsteorin beskriver intoleransen som en patologisk ökning av neural aktivitet. Betingningsteorin beskriver kemisk intolerans som ett resultat av grundläggande associativa inlägningsmekanismer. Slutligen beskriver teorin om neurogen inflammation intoleransen som en förhöjd aktivering av c-fiberaktivitet och ökade inflammatoriska processer. Huvudargumentet i den teoretiska sammanfattningen är att dessa teorier erbjuder komplementära perspektiv på kemisk intolerans. Med ett integrerat perspektiv kan förhoppningsvis infekterade debatter om huruvida kemisk intolerans är en psykologisk eller organisk åkomma undvikas.De oförklarade egenskaperna av kemisk intolerans, de empiriska fynden, samt de teoretiska förklaringarna beskrivs slutligen inom ett teoretiskt ramverk som utgår från signaldetektionsteorin. Flera egenskaper hos kemisk intolerans beskrivs i termer av ett förändrat eller lågt satt kriterium (ß).

Place, publisher, year, pages
Umeå: Department of Psychology, Umeå University, 2012.
Keyword [en]
Chemical Intolerance, Unexplained Medical Symptoms, Environmental Intolerance, Event-related potentials, functional magnetic resonance imaging, psychophysics, sensitization, habituation
National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:umu:diva-50569 (URN)978-91-7459-345-7 (ISBN)oai:DiVA.org:umu-50569 (OAI)
Public defence
2012-01-20, Norra beteendevetarhuset, HS1031, Umeå Universitet, Umeå, 13:15 (English)
Opponent
Supervisors
Available from2011-12-21 Created:2011-12-14 Last updated:2011-12-15Bibliographically approved
List of papers
1. Attention bias and sensitization in chemical sensitivity
Open this publication in new window or tab >>Attention bias and sensitization in chemical sensitivity
2009 (English)In: Journal of Psychosomatic Research, ISSN 0022-3999, E-ISSN 1879-1360, Vol. 66, no 5, 407-416Artikel i tidskrift (Refereed) Published
Abstract [en]

ObjectiveWe investigated whether persons with self-reported chemical sensitivity (CS) have an attention bias and enhanced sensitization to chemical exposure.MethodsChemosomatosensory, olfactory, and auditory event-related potentials (ERPs) were recorded from 21 CS subjects and 17 controls in attend and ignore conditions. Reaction times (RTs) and magnitude estimations of perceived intensity were collected in the attend condition. ERPs were averaged over attention conditions and during the first/second part of the testing.ResultsERP patterns indicated that CS subjects did not habituate to the same extent as the controls and had difficulties ignoring the chemical exposure. CS subjects had faster overall RT, and the perceived intensities for the chemosomatosensory stimuli did not decrease with time in the CS group, which was the case for the controls.ConclusionsThese results indicating attention bias and enhanced sensitization in CS suggest alterations in central, cognitive responses to chemical exposure.

Elsevier, 2009
Keyword
Attention bias, Chemical sensitivity, Event-related potentials, Psychophysics, Sensitization
National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:umu:diva-21749 (URN)10.1016/j.jpsychores.2008.11.005 (DOI)
Available from2009-04-20 Created:2009-04-20 Last updated:2011-12-15Bibliographically approved
2. On the relation between capsaicin sensitivity and responsiveness to CO2
Open this publication in new window or tab >>On the relation between capsaicin sensitivity and responsiveness to CO2 : detection sensitivity and event-related brain potentials
2009 (English)In: International Archives of Occupational and Environmental Health, ISSN 0340-0131, E-ISSN 1432-1246, Vol. 82, no 3, 285-290Artikel i tidskrift (Refereed) Published
Abstract [en]

Sensory hyperreactivity (SHR) with predominantly airway symptoms is a subgroup of chemical intolerance to various environmental substances with pungent/odorous properties. The hallmark of SHR is sensitivity to capsaicin inhalation, resulting in extensive coughing likely to be mediated by a C-fiber hyperreactivity of the airway sensory neurons. However, it is not clear whether capsaicin sensitivity implies a greater sensitivity to chemosomatosensory substances in general. Therefore, the present study tested the hypothesis of an association between capsaicin cough sensitivity and sensitivity to CO2 with respect to detection sensitivity and electrophysiological brain response.

Methods A correlational study was employed to investigate the relation between capsaicin cough sensitivity and detection thresholds and chemosomatosensory event-related potentials (ERPs) for CO2 presented in the nasal cavity in 35 persons varying in capsaicin cough sensitivity.

Results Number of coughs were found to correlate negatively with CO2 threshold and tended to correlate negatively also with N1 and P2 latencies of the chemosomatosensory ERP for CO2. No tendencies of correlations were found between number of coughs and latencies for olfactory and auditory ERPs, recorded for comparison, but, unexpectedly, were found between number of coughs and auditory N1 amplitude.

Conclusions The results imply that capsaicin cough sensitivity, such as in SHR, is related to higher detection sensitivity, and tends to be related to faster cortical processing of other chemosomatosensory substances, at least of CO2.

Keyword
Chemosomatosensory, ERPs, Multiple chemical sensitivity, Sensory hyperreactivity, Threshold
National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:umu:diva-19691 (URN)10.1007/s00420-008-0333-1 (DOI)
Available from2009-03-09 Created:2009-03-09 Last updated:2011-12-15Bibliographically approved
3. Chemosensory attention, habituation and detection in women and men
Open this publication in new window or tab >>Chemosensory attention, habituation and detection in women and men
2011 (English)In: International Journal of Psychophysiology, ISSN 0167-8760, E-ISSN 1872-7697, Vol. 79, 316-322Artikel i tidskrift (Refereed) Published
Abstract [en]

 The aim of this study was to investigate whether there are differences between women and men in how chemosensory stimuli are processed. Event-related potentials from 36 participants (18 men) showed that women had larger P3 amplitudes when attending, but not when ignoring CO 2 but not for n-butanol, compared with men. The main finding was that women and men differ in cognitive measures of chemosensory processing. 

Elsevier, 2011
Keyword
Olfaction, Chemosomatosensation, Attention, Habituation, Event-related potentials, Gender
National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:umu:diva-40416 (URN)10.1016/j.ijpsycho.2010.11.008 (DOI)
Available from2011-02-23 Created:2011-02-23 Last updated:2011-12-15Bibliographically approved

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