Subliminally Perceived Odours Modulate Female Intrasexual Competition: An Eye Movement Study

Background: Evidence suggests that subliminal odorants influence human perception and behavior. It has been hypothesized that the human sex-steroid derived compound 4,16-androstadien-3-one (androstadienone) functions as a human chemosignal. The most intensively studied steroid compound, androstadienone is known to be biologically relevant since it seems to convey information about male mate quality to women. It is unclear if the effects of androstadienone are menstrual cycle related. Methodology/Principal Findings: In the first experiment, heterosexual women were exposed to androstadienone or a control compound and asked to view stimuli such as female faces, male faces and familiar objects while their eye movements were recorded. In the second experiment the same women were asked to rate the level of stimuli attractiveness following exposure to the study or control compound. The results indicated that women at high conception risk spent more time viewing the female than the male faces regardless of the compound administered. Women at a low conception risk exhibited a preference for female faces only following exposure to androstadienone. Conclusions/Significance: We contend that a woman’s level of fertility influences her evaluation of potential competitors (e.g., faces of other women) during times critical for reproduction. Subliminally perceived odorants, such as androstadienone, might similarly enhance intrasexual competition strategies in women during fertility phases not critica

Chemosensory Cues to Conspecific Emotional Stress Activate Amygdala in Humans

Alarm substances are airborne chemical signals, released by an individual into the environment, which communicate emotional stress between conspecifics. Here we tested whether humans, like other mammals, are able to detect emotional stress in others by chemosensory cues. Sweat samples collected from individuals undergoing an acute emotional stressor, with exercise as a control, were pooled and presented to a separate group of participants (blind to condition) during four experiments. In an fMRI experiment and its replication, we showed that scanned participants showed amygdala activation in response to samples obtained from donors undergoing an emotional, but not physical, stressor. An odor-discrimination experiment suggested the effect was primarily due to emotional, and not odor, differences between the two stimuli. A fourth experiment investigated behavioral effects, demonstrating that stress samples sharpened emotion-perception of ambiguous facial stimuli. Together, our findings suggest human chemosensory signaling of emotional stress, with neurobiological and behavioral effects

The roles of the main and accessory olfactory systems in the detection of social odors in mice

Our understanding of olfaction has been built on the study of monomolecular (pure) odors, which are easily obtained and well characterized chemically. For most species social odors have far greater biological relevance than typical monomolecular odors, but much less is known about the neural circuits that process them. Three studies were conducted to further explore the neural pathways that process social odors in mice. In Study 1, a Go-No-Go olfactory discrimination task was used to ask whether social odors are more salient stimuli than non-social odors in males and females under different hormonal conditions. Performance (percent correct) was greater in males than females, and poorer in subjects without circulating gonadal hormones when mice were required to discriminate between two social odors (male versus female urine), but not when non-social odors (banana versus peppermint) were used. This suggests that social odors are more salient stimuli than non-social odors but only when gonadal hormones are present. The piriform cortex (PC) is the primary cortical target for volatile odors processed by the main olfactory system (MOS); whether the PC responds to social odor volatiles is not known. In Study 2 I recorded extracellularly from PC pyramidal neurons before and during exposure to urinary volatiles or amyl acetate (banana) in anesthetized males. Neuronal spiking was strongly dependent on testosterone levels. Notably, social odor exposure only weakly induced spiking, which contrasts with the strong behavioral effects these odors are known to induce, so it is likely that other, unknown pathways are more important for their detection. Non-volatile components of social odors are processed by the accessory olfactory system (AOS); however, the role of the AOS during ongoing social interactions is not clear. In Study 3 I used optogenetic activation of the AOB during mating to enhance signaling in the AOS of males; I found that this stimulation significantly increased copulatory behavior efficiency, suggesting that AOB activity during mating facilitates males’ sexual arousal and reproductive performance. Overall these results reveal new properties of social odor processing in mice: sex differences, dependence on gonadal hormones, and a role during ongoing behavioral interactions

Auswirkungen von Androstadienon auf das menschliche Verhalten

Androstadienon (AND) ist ein Chemosignal, das z.B. im menschlichen Körperschweiß vorkommt. Im Rahmen dieser Arbeit soll systematisch gesammelt werden, ob in der Literatur konsistente Einflüsse von AND auf bestimmte Verhaltensreaktionen bei Menschen aufgezeigt wurden bzw. ob und wie AND unter besonderen Voraussetzungen wirkt. Dies wurde mittels systematischem Review erzielt. Mittels PRISMA Leitlinie wurde die Literatur strukturiert und analysiert. Die Ergebnisse von 24 Originalstudien, welche Verhaltensdaten unter Einfluss von AND veröffentlicht hatten, wurden in vier verschiedenen Kategorien miteinander verglichen: Auswirkungen auf das soziale Verhalten, auf die emotionale Reizverarbeitung bzw. Emotionsbewertung, auf die Attraktivitätsbewertung und Partnerwahl sowie Wachsamkeit und Gedächtnisleistung. Aufgrund unterschiedlicher Studiendesigns, unterschiedlicher Stichproben, Studienaufgaben, Konzentrationen und Präsentationen von AND sowie Inhomogenität der berichteten Ergebnisse konnte kein konsistenter Effekt von AND auf das Verhalten von Menschen aufgezeigt werden. Zum anderen wurde die Frage gestellt, ob AND unterschiedliche Einflüsse auf Menschen hat, welche den Geruch von AND als angenehm oder unangenehm empfinden – hierfür wurden die Teilnehmenden einer Verhaltensstudie anhand Mediansplits hinsichtlich der Bewertung, wie angenehm sie die AND-Lösung empfunden haben, in zwei Gruppen geteilt und Unterschiede in Bezug auf zwei Aufmerksamkeitsprozesse untersucht. Vergleichbar zum systematischen Review konnte auch in der Verhaltensstudie kein konsistenter Effekt der subjektiv wahrgenommenen Annehmlichkeit von AND auf unterschiedliche Aufmerksamkeitsprozesse festgestellt werden. Zusammenfassend zeigt sich eine Inkonsistenz der publizierten Auswirkung von AND im systematischen Review. In der eigenen Studie konnten wir keinen Effekt der Annehmlichkeit von AND auf Aufmerksamkeitseffekte zeigen. Es bleibt daher offen, welchen Effekt AND tatsächlich auf menschliches Verhalten ausübt und zukünftige Forschung wird zeigen, welchen (konsistenten) Einfluss Chemosignale auf die menschliche Kommunikation haben