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Abstract: Olfactory perception in humans is characterized by salient emotional reactions that reflect our preferences. These preferences are modified by external and internal factors and when designing their studies, sensory scientists should take into account these modulators of olfactory perception. The present review is aimed at describing these factors that affect our affective responses to odors. A number of these modulators are related to the odorant characteristics. Other factors that influence the perceivers refer to the inter-individual variations according to sex, reproductive status and intraindividual changes occurring throughout the human life-span. Finally, relevant factors also stem from the experimental context where the smell is perceived. [Copyright &y& Elsevier]

• As experiences of pleasure and displeasure, hedonics are omnipresent in daily life. • As core processes, hedonics accompany emotions, motivation, bodily states, etc. • Orbitofrontal cortex and nucleus accumbens appear to be hedonic brain hubs. • Several mental illnesses are characterized by altered hedonic experiences. • Optimal hedonic functioning seems the basis of well-being and aesthetic experiences. Experiencing pleasure and displeasure is a fundamental part of life. Hedonics guide behavior, affect decision-making, induce learning, and much more. As the positive and negative valence of feelings, hedonics are core processes that accompany emotion, motivation, and bodily states. Here, the affective neuroscience of pleasure and displeasure that has largely focused on the investigation of reward and pain processing, is reviewed. We describe the neurobiological systems of hedonics and factors that modulate hedonic experiences (e.g., cognition, learning, sensory input). Further, we review maladaptive and adaptive pleasure and displeasure functions in mental disorders and well-being, as well as the experience of aesthetics. As a centerpiece of the Human Affectome Project, language used to express pleasure and displeasure was also analyzed, and showed that most of these analyzed words overlap with expressions of emotions, actions, and bodily states. Our review shows that hedonics are typically investigated as processes that accompany other functions, but the mechanisms of hedonics (as core processes) have not been fully elucidated. [ABSTRACT FROM AUTHOR]

• Humans communicate their emotions to others through body odors. • Previous studies show that positive emotions can be chemically communicated this way. • We increased efficacy of positive emotion induction using virtual reality (VR). • But evidence of chemical communication of emotion using VR were limited. • Chemical communication of emotion is subtle and difficult to detect in the laboratory. Humans can communicate their emotions to others via volatile emissions from their bodies. Although there is now solid evidence for human chemical communication of fear, stress and anxiety, investigations of positive emotions remain scarce. In a recent study, we found that women's heart rate and performance in creativity tasks were modulated by body odors of men sampled while they were in a positive vs. neutral mood. However, inducing positive emotions in laboratory settings remains challenging. Therefore, an important step to further investigate the human chemical communication of positive emotions is to develop new methods to induce positive moods. Here, we present a new mood induction procedure (MIP) based on virtual reality (VR), that we assumed to be more powerful than videos (used in our previous study) to induce positive emotions. We hypothesized that, consequently, given the more intense emotions created, this VR-based MIP would induce larger differences between the receivers' responses to the positive body odor versus a neutral control body odor, than the Video-based MIP. The results confirmed the higher efficacy of VR to induce positive emotions compared with videos. More specifically, VR had more repeatable effects between individuals. Although positive body odors had similar effects to those found in the previous video study, especially faster problem solving, these effects did not reach statistical significance. These outcomes are discussed as a function of the specificities of VR and of other methodological parameters, that may have prevented the observation of such subtle effects and that should be understood more in-depth for future studies on human chemical communication. [ABSTRACT FROM AUTHOR]

There is increasing evidence that human body odor is involved in interpersonal communication. However, among the wide variety of substances excreted by the human body that might act as chemosignals, much attention has been granted to androstenes to the detriment of other categories. Here, we focused on the acidic fraction of human body odor. We investigated men and women's perceptual descriptions and detection thresholds of the sexually dimorphic (male) compound 3-hydroxy-3-methylhexanoic acid (HMHA) in two contrasted cultures, France and Madagascar. Perceptual responses to HMHA in both countries were very similar. HMHA proved to be more typical of body odor than another chemically-related major compound of human body odor 3MHA (3-methylhex-2-enoic acid also known as 3M2H). A significant portion of the samples studied (between 8 and 19%) was likely to be anosmic to HMHA (and to 3MHA: 25%). Although differences would be expected between men and women's perceptual responses to HMHA, based on the assumption that this compound would have a function in human partner choice, no sex differences were found for any of the perceptual variables. However, in Malagasy women, perceived intensity of HMHA was higher in participants who were in the fertile phase of the menstrual cycle. Whether HMHA is relevant in the perception of a potential partner thus requires further explorations, with more implicit approaches for example and/or by investigating the repercussions of HMHA specific anosmia on interpersonal relationships. • The role of chemical communication in human attractiveness remains poorly understood. • Besides the classically studied androstenes, other compounds need to be considered. • This study investigates how a carboxylic acid of human body odor (HMHA) is perceived. • No sex differences emerged, but fertile women perceived HMHA as more intense. • Large interindividual (but little cultural) variability was found. [ABSTRACT FROM AUTHOR]