Human olfactory detection of homologous n-alcohols measured via concentration-response functions

We explored in humans concentration-detection functions for the odor of the homologous n-alcohols ethanol, 1-butanol, 1-hexanol, and 1-octanol. These functions serve to establish structure-activity relationships, and reflect the pharmacology of the olfactory sense at the behavioral level. We tested groups of 14 to 17 subjects (half of them females), averaging 31 to 35 years old. An 8-station vapor delivery device (VDD8) presented the stimulus under a three-alternative forced-choice procedure against carbon-filtered air. The VDD8 was built to meet the demands of typical human sniffs in a short-term (<5 s) olfactory detection task, and to accurately control odorant generation, delivery, and stability. Actual stimulus concentration was quantified by gas chromatography before and during testing. The functions obtained were log normally distributed and were accurately modeled by a sigmoid (logistic) function, both at the group and at the individual level. Sensitivity to ethanol was the lowest and to 1-octanol the highest. Functions became steeper with increasing carbon chain length. For all alcohols the concentration detected halfway between chance and perfect detection (threshold) was at the ppb (or nM) level. Females were slightly more sensitive than males. Intersubject variability across participants was between one and two orders of magnitude. The present odor thresholds were lower than many reported in the past but their relative pattern across alcohols paralleled that in our earlier data and in compilation studies. A previously described quantitative structure-activity relationship for odor potency holds promise to model thresholds that, like those obtained here, best reflect the intrinsic sensitivity of human olfaction.