On the Trigeminal Percept of Androstenone and Its Implications on the Rate of Specific Anosmia Julie A. Boyle, 1 Johan N. Lundstro ¨ m, 1 Michael Knecht, 2 Marilyn Jones-Gotman, 1 Benoist Schaal, 3 Thomas Hummel 2 1 Montreal Neurological Institute, McGill University, Montreal, Canada 2 Department of Otorhinolaryngology, University of Dresden Medical School (\Technische Universita ¨ t Dresden"), Dresden, Germany 3 Centre des Science du Gout, CNRS, Dijon, France Received 11 February 2006; accepted 28 March 2006 ABSTRACT: Specific anosmia is a term that de- scribes an inability to perceive a particular odorant in the context of an otherwise normal olfactory acuity. The most common example, for the odor of androstenone, has been ascribed a prevalence ranging from 2 to 45%. In two experiments we sought to determine whether this wide range could be explained by the difference in ste- roid concentrations used, and by the degree to which the trigeminal system contributes to perception of androste- none. Experiment 1 demonstrated that high concentra- tions of androstenone stimulated the trigeminal system, as indicated by electrophysiological recordings. Experi- ment 2 demonstrated that conscious detection of andros- tenone is possible based solely on the trigeminal system. Interestingly, detection seems to interact with olfactory acuity in that subjects with a low olfactory sensitivity to androstenone were better able to detect its trigeminal component. The agreement between conscious experi- ence and behavioral discrimination was not well cali- brated, in that subjects demonstrated a clear overconfi- dence in their abilities. Altogether, the current study suggests that androstenone is an odorant that produces a concentration-dependent degree of trigeminal stimula- tion. This trigeminal component explains the diversity of the reported prevalence of specific anosmia for androstenone and might have implications on future use of specific anosmia as a tool to understand odor process- ing. ' 2006 Wiley Periodicals, Inc. J Neurobiol 66: 1501–1510, 2006 Keywords: sensitivity; NMP; lateralization task; tri- geminal system; confidence The existence of specific anosmias has been known for almost two centuries (cf. Cloquet, 1821; Reuter, 1893). However, the term \specific anosmia" was defined only 40 years ago as a condition in which an individual with normal olfactory functions is incapa- ble of perceiving a particular odor (Amoore, 1967). Specific anosmia to the odorous steroid 5-androst- 16-en-3-one (androstenone) has been a classical example, and as such has been extensively investi- gated. This endogenous compound can be found in both human secretion and excretion in a concentra- tion up to 15 pmol/mg in the axillary hair (Nixon et al., 1988) and 40–603 ng/L in the apocrine secre- tion of men (Labows and Preti, 1992). In women, the steroid is present in much lower concentrations, if at all (Zeng et al., 1996). Specific anosmia to androste- none has been found, at least to some degree, to be genetically determined (Wysocki and Beauchamp, Correspondence to: J.N. Lundstro ¨m (johan.lundstrom@mcgill. ca). Contract grant sponsor: Canadian Institutes of Health Research; contract grant number: MOP-57846 (M.J.G.). Contract grant sponsor: Deutsche Forschungsgemeinschaft; con- tract grant number: DFG HU441/2 (T.H.). ' 2006 Wiley Periodicals, Inc. Published online 29 September 2006 in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/neu.20294 1501