Synergy and masking in odor mixtures: an electrophysiological study of orthonasal vs. retronasal perception.

Perceptual interactions in a model of wine woody-fruity binary mixtures were previously reported in a psychophysical study performed through orthonasal stimulation only. However, recent studies suggested that the perception of food-like and nonfood-like odors may depend on the route of stimulation. The aim of the present study was two-fold: first to examine the neural correlates of perceptual interactions using electroencephalogram (EEG)-derived event-related potentials (ERPs) and second to test the influence of the stimulation route on quality perception. Therefore, we designed an experiment with 30 subjects to study perceptual interactions in woody-fruity mixtures and compared ortho- vs. retronasal stimulation sites on perceived odor quality and ERPs. The results revealed synergy or masking of the fruity component, depending on the woody component level. Synergy was supported by larger N1 amplitude of the ERP. Furthermore, mixtures including a medium level of the woody odor elicited a strong increase of P2 amplitude only retronasally. This study evidenced for the first time electrophysiological correlates of both perceptual synergy and masking on the early component of the ERPs and confirmed that retro- vs. orthonasal stimulation route induces different neural processes that are reflected in the late component of the ERP.

Intranasal trigeminal function in children.

The aim of the study was to investigate trigeminal function in children compared with that of adults. Trigeminal sensitivity was assessed using a lateralization task where participants were requested to identify the side of the nose to which an odorous stimulus was presented. The ability to localize the sensation is largely based on trigeminal function. A total of 344 people participated (191 females, 153 males; mean age 12 y [SD 7 y 9 mo], range 5-54 y). Eucalyptol (EUC) was administered as a mixed olfactory-trigeminal stimulant; phenylethyl alcohol (PEA) was used as a control stimulant with minimal trigeminal impact. In addition, sensitivity to vibration was assessed as a somatosensory control. With regard to all age groups, PEA could not be localized whereas this was easily possible for EUC. However, the ability to localize EUC increased with age, which was not the case for PEA. No sex-related difference was found for odour localization. These results provide data for normal intranasal trigeminal function in children. They also indicate that trigeminal sensitivity is already well-developed in children.