International Dairy Journal 18 (2008) 874–878 Olfactory event-related potentials in response to ortho- and retronasal stimulation with odors related or unrelated to foods Thomas Hummel à , Stefan Heilmann Smell and Taste Clinic, Department of Otorhinolaryngology, University of Dresden Medical School, Fetscherstrasse 74, 01307 Dresden, Germany Received 31 August 2007; accepted 31 October 2007 Abstract The aim of this study was to investigate the perception of odor intensity following ortho- and retronasal odor presentation and to simultaneously study differences between ortho- and retronasal olfaction using an electrophysiological measure event-related potentials (ERP). Using air-dilution olfactometry, 24 young healthy subjects were investigated. For retro- and orthonasal stimulation, a technique was used that allowed precise control of stimulus characteristics. To investigate potential distinctions between the processing of food and non-food related odors, lavender and chocolate odors were used. Results indicated that, when an odor unrelated to food was presented in an unusual site, i.e., retronasally, the response was larger compared with presentation of the same odor at an orthonasal site. This was the other way around for a food-related odor. These changes indicate differences of information processing depending on the context and the route of odor presentation which has direct implications for the enjoyment of foods and drinks. r 2007 Elsevier Ltd. All rights reserved. Keywords: Retronasal olfaction; Psychophysics; Electrophysiology 1. Introduction Due to its significant role in the perception of aromas, retronasal olfaction has been the subject of numerous studies (e.g., Burdach & Doty, 1987; Burdach, Kroeze, & Koster, 1984; Cerf-Ducastel & Murphy, 2001; Heilmann, Strehle, Rosenheim, Damm, & Hummel, 2002; Pierce & Halpern, 1996) although considerably less information is available compared with research on orthonasal olfactory function which is probably largely due to technical limitations. Previous reports in literature give different opinions about the performance of the retronasal olfactory system. Pierce and Halpern (1996) report a diminished identifica- tion ability through the retronasal pathway using the oral presentation of the vapor phase of solid odorous sub- stances. However, the experiments of Voirol and Daget (1986) have shown an increased sensitivity for the retro- nasal presentation of vaporous odorants in liquids. In this study, subjects sniffed the headspace of a liquid containing an odorant and sampled the liquid orally. However, these studies used the oral application of substances, which might influence odor perception by oral stimulation. As shown by Dalton, Doolittle, Nagata, and Breslin (2000) even across modalities, sub-threshold stimulation of taste and smell might result in a complex oral sensation. Therefore, studies using oral stimulation might face undetected interactions, even if the used liquid alone does not have supra-threshold taste properties. With regard to the difference between ortho- and retronasal olfactory function, most recent work indicated that these are indeed two separate entities, as hypothesized earlier by Rozin (1982). It has been shown that habituated salivation rates recovered when the route of odor presentation was changed ortho- to retronasal or vice versa. Importantly, this dishabituation was seen without the subjects knowing that the route of odor presentation had been changed (Bender, Small, Negoias, & Hummel, 2007). In addition, studies based on functional magnetic resonance imaging revealed that orthonasal presentation of an odor produced very different patterns of activation ARTICLE IN PRESS www.elsevier.com/locate/idairyj 0958-6946/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.idairyj.2007.10.010 à Corresponding author. Tel.: +49 351 458 4189; fax: +49 351 458 4326. E-mail address: thummel@mail.zih.tu-dresden.de (T. Hummel).