Sex-steroid derived compounds induce sex-specific effects on autonomic nervous system function in humans

Little evidence that androstadienone affects social distance-dependent prosocial behaviour: a pre-registered study

In navigating the complexities of social life, humans have evolved to interpret invisible odorous chemical cues, with profound behavioural impacts often unbeknown to the conscious mind. The manifestation of this in humans is evident in the scent of androstadienone (androsta-4,16-dien-3-one), an odorous compound which is considered a putative human pheromone. The current study investigated the effect of androstadienone on social distance-dependent prosocial behaviour measured by a social discounting task, in which participants chose between selfish and generous options. Based on our pre-registration, we predicted a sex-specific effect, with males exposed to androstadienone exhibiting increased generosity, while females would choose more selfishly. Employing a double-blind, placebo-controlled, between-subject design, we recruited 170 participants who were randomly assigned to either the androstadienone or control condition. Olfactory stimuli were administered while participants completed the social discounting task. Inconsistent with our hypothesis, inhaling androstadienone did not impact social distance-dependent prosocial behaviour. This finding was supported by multiple estimates of prosociality, including model-free, model-based and maximum likelihood estimation. Further analyses indicated that androstadienone administration did not influence perceived social distance or bias participants towards being generous or selfish. Thus, our empirical findings provide no support for the hypothesis that androstadienone modulates generosity.

Sex-specific effects of human chemosignal on perception of angry but not fearful faces

Androsta-4,16,-dien-3-one (androstadienone), a steroids implicated as a human social chemosignal, has been reported to impact one's emotional perception along the valence axis. The current study takes a step further to examine whether it modulates the perception of angry and fearful faces, two negative emotions that are similar with respect to valence and arousal, but signal different social values. Systematic comparisons of psychophysical data collected from 40 heterosexual men and 45 heterosexual women revealed that androstadienone subconsciously biased heterosexual men toward perceiving the male faces as less angry, while it biased the heterosexual women toward perceiving the female faces as angrier. Meanwhile, androstadienone did not affect the perception of fearful faces in either men or women. These findings indicate that the modulation of androstadienone on negative emotional perceptions is not uniform, suggesting that it alters the perception of specific rather than general negative emotions. In particular, it impacts one's perception of anger, which signals impending aggression, and hence could further impact an individual's social interaction in a sex-specific manner.

Improving speech characteristics of young adults with congenital dysarthria: An exploratory study comparing articulation training and the Beatalk method

INTRODUCTION

This exploratory study compared the effects of two speech therapy approaches on speech characteristics of young adults with congenital dysarthria resulting from various etiologies: a) articulation training focusing on consonant articulation exercises at various levels (isolation, syllables, and words), and b) the Beatalk method, based on human beatboxing, i.e., producing various instrumental sounds in an a-cappella musical context. Both interventions were designed to increase participants' speech intelligibility.

METHODS

Twelve adults with congenital dysarthria and reduced speech intelligibility participated in treatment groups for eight weeks. Six participants were assigned to the articulation training group, and six to the Beatalk group. Intelligibility of single words and continuous speech, voice measures, and oral-diadochokinesis rates were measured before and after the treatment.

RESULTS

The results showed that the Beatalk intervention yielded a significant overall pre- to post-treatment effect. Specifically, it resulted in gains in articulatory accuracy and intelligibility for single words. Improvements were not noted following articulation training.

CONCLUSIONS

The results present initial evidence of the positive effect of the Beatalk method as an intervention tool for adults with congenital dysarthria. This relatively easy-to-learn technique shows promise, as it involves intense and repetitive production of speech sounds while controlling rhythm and breathing in an enjoyable context.

The scent of attraction and the smell of success: crossmodal influences on person perception

In recent decades, there has been an explosion of research into the crossmodal influence of olfactory cues on multisensory person perception. Numerous peer-reviewed studies have documented that a variety of olfactory stimuli, from ambient malodours through to fine fragrances, and even a range of chemosensory body odours can influence everything from a perceiver's judgments of another person's attractiveness, age, affect, health/disease status, and even elements of their personality. The crossmodal and multisensory contributions to such effects are reviewed and the limitations/peculiarities of the research that have been published to date are highlighted. At the same time, however, it is important to note that the presence of scent (and/or the absence of malodour) can also influence people's (i.e., a perceiver's) self-confidence which may, in turn, affect how attractive they appear to others. Several potential cognitive mechanisms have been put forward to try and explain such crossmodal/multisensory influences, and some of the neural substrates underpinning these effects have now been characterized. At the end of this narrative review, a number of the potential (and actual) applications for, and implications of, such crossmodal/multisensory phenomena involving olfaction are outlined briefly.

Pheromone effects on the human hypothalamus in relation to sexual orientation and gender

Pheromones are chemicals that serve communicational purposes within a species. In most terrestrial mammals, pheromones are detected by either the olfactory epithelium or the vomeronasal organ and processed by various downstream structures including the medial amygdala and the hypothalamus to regulate motivated behaviors and endocrine responses. The search for human pheromones began in the 1970s. Whereas bioactive ligands are yet to be identified, there has been accumulating evidence that human body odors exert a range of pheromone-like effects on the recipients, including triggering innate behavioral responses, modulating endocrine levels, signaling social information, and affecting mood and cognition. In parallel, results from recent brain imaging studies suggest that body odors evoke distinct neural responses from those observed with common nonsocial odors. Two endogenous steroids androsta-4,16,- dien-3-one and estra-1,3,5(10),16-tetraen-3-ol are considered by some as candidates for human sex pheromones. The two substances produce sexually dimorphic effects on human perception, mood, and physiological arousal. Moreover, they reportedly elicit different hypothalamic response patterns in manners contingent on the recipients' sex and sexual orientation. Neuroendocrine mechanisms underlying the effects of human chemosignals are not yet clear and await future detailed analyses.

Chemical Fingerprints of Emotional Body Odor

Chemical communication is common among animals. In humans, the chemical basis of social communication has remained a black box, despite psychological and neural research showing distinctive physiological, behavioral, and neural consequences of body odors emitted during emotional states like fear and happiness. We used a multidisciplinary approach to examine whether molecular cues could be associated with an emotional state in the emitter. Our research revealed that the volatile molecules transmitting different emotions to perceivers also have objectively different chemical properties. Chemical analysis of underarm sweat collected from the same donors in fearful, happy, and emotionally neutral states was conducted using untargeted two-dimensional (GC×GC) coupled with time of flight (ToF) MS-based profiling. Based on the multivariate statistical analyses, we find that the pattern of chemical volatiles (N = 1655 peaks) associated with fearful state is clearly different from that associated with (pleasant) neutral state. Happy sweat is also significantly different from the other states, chemically, but shows a bipolar pattern of overlap with fearful as well as neutral state. Candidate chemical classes associated with emotional and neutral sweat have been identified, specifically, linear aldehydes, ketones, esters, and cyclic molecules (5 rings). This research constitutes a first step toward identifying the chemical fingerprints of emotion.

[Modern studies of the role of the vomeronasal system in the perception of pheromones and their impact on social and sexual behavior]

The vomeronasal system (VNS) provides regulation of a wide range of autonomic and affective functions, behavioral reactions in response to the specific chemical stimuli pheromones secreted by mammals, including humans. The results of experimental studies confirming the existence of VNS and explaining the basic mechanisms of its functioning are presented. The results of studies of healthy volunteers, explaining the effect of pheromones on a number of functions of the human body, are considered.

Inter- and Intra-Species Communication of Emotion: Chemosignals as the Neglected Medium

Human body odors contain chemosignals that make species-specific communication possible. Such communication is without communicative intent and is generally below the threshold of consciousness. Human recipients of these chemosignals produced during emotional conditions display a simulacrum of the emotional state under which the chemosignal was produced. The investigation of an inter-species transfer of emotions via chemosignals was initiated by considerations of the historically anchored interdependence between humans and domesticated species, such as dogs and horses. Indeed, experiments with dogs have demonstrated that human body odors produced under emotional conditions of happiness and fear led dogs to manifest corresponding emotions to those experienced by humans. Preliminary data from horses also show that human body odors collected under fear and happiness conditions activate the autonomic nervous system of horses differentially. These studies indicate the possibility of a road to open our understanding of inter-species emotional communication via chemosignals.

The effect of complete caloric intake restriction on human body odour quality

Previous studies on various vertebrates have shown that quantity and quality of food intake affect odour attractiveness as perceived by potential mates. In humans, the quality of body odour is similarly affected by ingested foods, such as by variation in meat and garlic intake. Nevertheless, it is not known whether quantity of food has an impact on human body odour attractiveness. Thus, here we tested how 48 h of complete caloric intake restriction affects the hedonic quality of human axillary odour. Odour samples (cotton pads fixed in both armpits and worn for 12 h) were obtained from healthy female donors across three conditions: i) during their habitual food regime; ii) after 48 h of complete caloric intake restriction (drinking water was provided), and iii) 72 h after restoration of caloric intake. Axillary samples were assessed by male raters regarding their pleasantness, attractiveness, femininity, and intensity. We also collected blood samples to assess physiological changes due to dietary restriction (e.g., glucose, sodium, albumin, and triacylglyceride assays) and anthropometric measurements at the same intervals as body odour samples. We found no differences in pleasantness, attractiveness and intensity between the odour samples collected at baseline and during complete caloric intake restriction. Interestingly, we found that body odours were rated more pleasant, more attractive and less intense after restoration of food intake as compared to the baseline and during caloric restriction. Our results suggest that restoration of food intake positively influences hedonic quality of human body odour which might thus provide cues to current fitness status and metabolic efficiency.

Human chemosignals modulate emotional perception of biological motion in a sex-specific manner

Androsta-4,16,-dien-3-one and estra-1,3,5(10),16-tetraen-3-ol have previously been shown to communicate opposite sex information that is differently effective to the two sex groups. The current study critically examines if the two human steroids could facilitate interactions with potential mates rather than competitors by acting on the recipients' emotional perception in a sex-appropriate manner. Using dynamic point-light displays that portray the gaits of walkers whose emotional states are digitally morphed along the valence and the arousal axes, we show that smelling androstadienone subconsciously biases heterosexual women, but not men, towards perceiving the male, but not female, walkers as happier and more relaxed. By contrast, smelling estratetraenol subconsciously biases heterosexual men, but not women, towards perceiving the female, but not male, walkers as happier and more relaxed. These findings indicate that androstadienone and estratetraenol prime the identification of emotionally receptive states for the potential mates with whom they are associated, in manners contingent upon not only the recipients' own sex but also their sex perception of other individuals that ensure sex-appropriate behavior.

Altered responses to social chemosignals in autism spectrum disorder

Autism spectrum disorder (ASD) is characterized by impaired social communication, often attributed to misreading of emotional cues. Why individuals with ASD misread emotions remains unclear. Given that terrestrial mammals rely on their sense of smell to read conspecific emotions, we hypothesized that misreading of emotional cues in ASD partially reflects altered social chemosignaling. We found no difference between typically developed (TD) and cognitively able adults with ASD at explicit detection and perception of social chemosignals. Nevertheless, TD and ASD participants dissociated in their responses to subliminal presentation of these same compounds: the undetected 'smell of fear' (skydiver sweat) increased physiological arousal and reduced explicit and implicit measures of trust in TD but acted opposite in ASD participants. Moreover, two different undetected synthetic putative social chemosignals increased or decreased arousal in TD but acted opposite in ASD participants. These results implicate social chemosignaling as a sensory substrate of social impairment in ASD.

A missense polymorphism in the putative pheromone receptor gene VN1R1 is associated with sociosexual behavior

Pheromones regulate social and reproductive behavior in most mammalian species. These effects are mediated by the vomeronasal and main olfactory systems. Effects of putative pheromones on human neuroendocrine activity, brain activity and attractiveness ratings suggest that humans may communicate via similar chemosignaling. Here we studied two samples of younger and older individuals, respectively, with respect to one nonsynonymous polymorphism in the gene encoding the human vomeronasal type-1 receptor 1, VN1R1, and one nonsynonymous polymorphism in the gene encoding the olfactory receptor OR7D4. Participants in both samples had self-reported their sociosexual behavior using the sociosexual orientation inventory, including questions regarding lifetime number of one-night stands, number of partners last year and expected number of partners the coming 5 years. In women, there was a significant association between the VN1R1 polymorphism and sociosexual behavior in both samples, driven specifically by the question regarding one-night stands. Our results support the hypothesis that human social interaction is modulated by communication via chemosignaling.

A human chemosignal modulates frontolimbic activity and connectivity in response to emotional stimuli

Evidence suggests the putative human pheromone Δ4,16-androstadien-3-one (androstadienone), a natural component of human sweat, increases attention to emotional information when passively inhaled, even in minute amounts. However, the neural mechanisms underlying androstadienone's impact on the perception of emotional stimuli have not been clarified. To characterize how the compound modifies neural circuitry while attending to emotional information, 22 subjects (11 women) underwent two fMRI scanning sessions, one with an androstadienone solution and one with a carrier control solution alone on their upper lip. During each session, participants viewed blocks of emotionally positive, negative, or neutral images. The BOLD response to emotional images (relative to neutral images) was greater during exposure to androstadienone in right orbitofrontal and lateral prefrontal cortex, particularly during positive image blocks. Androstadienone did not impact the response to social images, compared to nonsocial images, and results were not related to participant sex or olfactory sensitivity. To examine how androstadienone influences effective connectivity of this network, a dynamic causal model was employed with primary visual cortex (V1), amygdala, prefrontal cortex, and orbitofrontal cortex on each side. These models indicated that emotional images increased the drive from V1 to the amygdala during the control session. With androstadienone present, this drive to amygdala was decreased specifically for positive images, which drove downstream increases in orbitofrontal and prefrontal activity. This evidence suggests that androstadienone may act as a chemical signal to increase attention to positively valenced information via modifications to amygdala connectivity.

Interpreting ambiguous social cues in unpredictable contexts

Unpredictable environments can be anxiety-provoking and elicit exaggerated emotional responses to aversive stimuli. Even neutral stimuli, when presented in an unpredictable fashion, prime anxiety-like behavior and elicit heightened amygdala activity. The amygdala plays a key role in initiating responses to biologically relevant information, such as facial expressions of emotion. While some expressions clearly signal negative (anger) or positive (happy) events, other expressions (e.g. surprise) are more ambiguous in that they can predict either valence, depending on the context. Here, we sought to determine whether unpredictable presentations of ambiguous facial expressions would bias participants to interpret them more negatively. We used functional magnetic resonance imaging and facial electromyography (EMG) to characterize responses to predictable vs unpredictable presentations of surprised faces. We observed moderate but sustained increases in amygdala reactivity to predictable presentations of surprised faces, and relatively increased amygdala responses to unpredictable faces that then habituated, similar to previously observed responses to clearly negative (e.g. fearful) faces. We also observed decreased corrugator EMG responses to predictable surprised face presentations, similar to happy faces, and increased responses to unpredictable surprised face presentations, similar to angry faces. Taken together, these data suggest that unpredictability biases people to interpret ambiguous social cues negatively.

The search for human pheromones: the lost decades and the necessity of returning to first principles

As humans are mammals, it is possible, perhaps even probable, that we have pheromones. However, there is no robust bioassay-led evidence for the widely published claims that four steroid molecules are human pheromones: androstenone, androstenol, androstadienone and estratetraenol. In the absence of sound reasons to test the molecules, positive results in studies need to be treated with scepticism as these are highly likely to be false positives. Common problems include small sample sizes, an overestimate of effect size (as no effect can be expected), positive publication bias and lack of replication. Instead, if we are to find human pheromones, we need to treat ourselves as if we were a newly discovered mammal, and use the rigorous methods already proven successful in pheromone research on other species. Establishing a pheromone relies on demonstration of an odour-mediated behavioural or physiological response, identification and synthesis of the bioactive molecule(s), followed by bioassay confirmation of activity. Likely sources include our sebaceous glands. Comparison of secretions from adult and pre-pubertal humans may highlight potential molecules involved in sexual behaviour. One of the most promising human pheromone leads is a nipple secretion from the areola glands produced by all lactating mothers, which stimulates suckling by any baby not just their own.

A social chemosignaling function for human handshaking

Social chemosignaling is a part of human behavior, but how chemosignals transfer from one individual to another is unknown. In turn, humans greet each other with handshakes, but the functional antecedents of this behavior remain unclear. To ask whether handshakes are used to sample conspecific social chemosignals, we covertly filmed 271 subjects within a structured greeting event either with or without a handshake. We found that humans often sniff their own hands, and selectively increase this behavior after handshake. After handshakes within gender, subjects increased sniffing of their own right shaking hand by more than 100%. In contrast, after handshakes across gender, subjects increased sniffing of their own left non-shaking hand by more than 100%. Tainting participants with unnoticed odors significantly altered the effects, thus verifying their olfactory nature. Thus, handshaking may functionally serve active yet subliminal social chemosignaling, which likely plays a large role in ongoing human behavior.

DOI:http://dx.doi.org/10.7554/eLife.05154.001

Animals often sniff each other as a form of greeting to communicate with each other through chemical signals in their body odors. However, in humans this form of behavior is considered taboo, especially between strangers.

Scientists argue that, in spite of our efforts to avoid being ‘smelly’, we may actually smell each other without being aware that we do so. Here, Frumin et al. first put on latex gloves and then shook hands with volunteers to collect samples of their odor. Chemical analysis of the gloves found that a handshake alone was sufficient to transfer the volunteers' odor. These odors were made of chemicals that are similar to ones that animals smell when sniffing each other.

Therefore, when we shake hands with a stranger, it is possible that we may inadvertently smell the stranger's chemical signals. To address this possibility, Frumin et al. investigated how humans behave after shaking hands with a stranger. Volunteers were asked to wait in a room alone before they were greeted by one of the researchers. Some of these volunteers were greeted with a handshake and others were greeted without a handshake. Afterwards, all the volunteers spent some time in a room by themselves where their behavior was covertly monitored.

Frumin et al. found that volunteers who shook hands were more likely to sniff their hand, for example, by touching their nose when they were in the room on their own, than those who did not shake hands. After the volunteers shook hands with someone of their own gender, they spent more time sniffing their right hand (the one they had used for the handshake). However, after the volunteers shook hands with someone of the opposite gender, they spent more time sniffing their left hand instead.

Next, the body odor of some of the experimenters was tainted by perfumes or gender-specific odors. Volunteers who shook hands with these tainted individuals behaved differently; when the experimenter was tainted with perfume the volunteers spent more time sniffing their own hands, but when the experimenter was tainted with a gender-specific odor they spent less time sniffing of their own hands. This shows that different smells influenced the hand sniffing behavior of the volunteers.

Frumin et al.'s findings suggest that a simple handshake may help us to detect chemical signals from other people. Depending on the person's gender, we may respond by sniffing our right hand to check out the person's odor, or our left hand to smell ourselves in comparison. Future studies will involve finding out how this sniffing behavior could work as an unconcious form of human communication.

DOI:http://dx.doi.org/10.7554/eLife.05154.002

Always follow your nose: the functional significance of social chemosignals in human reproduction and survival

This article is part of a Special Issue "Chemosignals and Reproduction" Across phyla, chemosensory communication is crucial for mediating a variety of social behaviors, which form the basis for ontogenetic and phylogenetic survival. In the present paper, evidence on chemosensory communication in humans, with special reference to reproduction and survival, will be presented. First, the impact of chemosignals on human reproduction will be reviewed. Work will be presented, showing how chemosensory signals are involved in mate choice and partnership formation by communicating attractiveness and facilitating a partner selection, which is of evolutionary advantage, and furthermore providing information about the level of sexual hormones. In addition to direct effects on phylogenetic survival, chemosignals indirectly aid reproductive success by fostering harm protection. Results will be presented, showing that chemosensory communication aids the emotional bond between mother and child, which in turn motivates parental caretaking and protection, leading to infant survival. Moreover, the likelihood of group survival can be increased through the use of stress-related chemosignals. Stress-related chemosignals induce a stress-related physiology in the perceiver, thereby priming a fight-flight-response, which is necessary for an optimum adaption to environmental harm. Finally, effects of sexual orientation on chemosensory communication will be discussed in terms of their putative role in stabilizing social groups, which might indirectly provide harm protection and foster survival. An integrative model of the presented data will be introduced. In conclusion, an outlook, focusing on the involvement of chemosensory communication in human social behavior and illustrating a novel approach to the significance of chemosensory signals in human survival, will be given.

Sex steroids as pheromones in mammals: the exceptional role of estradiol

This article is part of a Special Issue (Chemosignals and Reproduction). Whether from endogenous or exogenous sources, 17β-estradiol (E2) has very powerful influences over mammalian female reproductive physiology and behavior. Given its highly lipophilic nature and low molecular mass, E2 readily enters excretions and can be absorbed from exogenous sources via nasal, cutaneous, and other modes of exposure. Indeed, systemic injection of tritiated estradiol ((3)H-E2) into a male mouse or bat has been shown to produce significant levels of radioactivity in the reproductive tissues and brain of cohabiting female conspecifics. Bioactive E2 and other steroids are naturally found in male mouse urine and other excretions, and males actively direct their urine at proximate females. Very low doses of E2 can mimic the Bruce effect (disruption of peri-implantation pregnancy by novel males), the Vandenbergh effect (early reproductive maturation induced by novel males), and male-induced estrus and ovulation. Males' capacities to induce the Bruce and Vandenbergh effects can both be diminished by manipulations that reduce their urinary E2. Uterine dynamics during the Bruce and Vandenbergh effects are consistent with the actions of E2. Collectively, these data demonstrate a critical role of male-sourced E2 in these major mammalian pheromonal effects.

Swelling of Erectile Nasal Tissue Induced by Human Sexual Pheromone

Most chemically mediated sexual communication in humans remains uncharacterized. Yet the study of sexual communication is decisive for understanding sexual behavior and evolutive mechanisms in our species. Here we provide the evidence to consider 4,16-androstadien-3-one (AND) as a man's sexual pheromone. Our experiment provides support for the physiological effect of AND on nasal airway resistance (Rna) in women, as assessed by anterior rhinomanometry. We found that AND administration increased the area of turbinate during the ovulatory phase, resulting in an increase of Rna. Thus, we discovered that minute amounts of AND, acting through neuroendocrine brain control, regulate Rna and consequently affect the sexual physiology and behavior. Fascinatingly, this finding provides the evidence of the preservation of chemosexual communication in humans, which it has been largely neglected due to its unconscious perception and concealed nature. Therefore, chemical communication is a plesiomorphic evolutive phenomenon in humans.

Localization of sex hormone binding globulin in the rat vomeronasal organ

Volatile and non-volatile derivates of gonadal steroids are known to act as pheromones in many mammalian species. Pheromones have multiple effects on the brain via the olfactory system. Their primary port of entry seems to be the vomeronasal organ (VNO) but the underlying cellular and molecular mechanisms are unclear so far. Recently we localized sex hormone binding globulin (SHBG) in both the main and the accessory olfactory system of rat with immunocytochemistry and RT-PCR. The accessory olfactory system consisting of VNO and accessory olfactory bulb showed high expression of SHBG. In the present paper we studied SHBG expression in the VNO in greater detail. In semithin sections we found SHBG immunostaining in the perinuclear cytoplasm of some of the sensory neurons, in sensory cilia and in their axons. A portion of the basal cells and some of the goblet cells in the non-sensory epithelium showed intense SHBG staining. SHBG was abundant in exocrine cells of the vomeronasal glands, perhaps compartimentalized in secretory vesicles. In situ hybridization revealed specific signals in sensory and non-sensory cells of the VNO. Our findings indicate that SHBG expressed in the VNO may be liberated into nasal secretions to bind aerosolic steroids. SHBG in sensory cells may be involved in signaling actions of pheromones.

Gender effects and sexual-orientation impact on androstadienone-evoked behavior and neural processing

In humans, the most established and investigated substance acting as a chemosignal, i.e., a substance that is excreted from the body, is 4,16-androstadien-3-one (AND). AND, which is found in sweat and saliva, is known to be responsible for influencing several variables, such as psychophysiological status, behavior, as well as cortical processing. The aim of the present review is to give insight into the variety of AND effects, with special regard to specific cross-sexual characteristics of this putative human chemosignal, emphasizing the neural activation patterns and factors such as contextual conditions. This review highlights the importance of including those contributing factors into the analysis of behavioral as well as brain-related studies.

Hypothalamic response to the chemo-signal androstadienone in gender dysphoric children and adolescents

The odorous steroid androstadienone, a putative male chemo-signal, was previously reported to evoke sex differences in hypothalamic activation in adult heterosexual men and women. In order to investigate whether puberty modulated this sex difference in response to androstadienone, we measured the hypothalamic responsiveness to this chemo-signal in 39 pre-pubertal and 41 adolescent boys and girls by means of functional magnetic resonance imaging. We then investigated whether 36 pre-pubertal children and 38 adolescents diagnosed with gender dysphoria (GD; DSM-5) exhibited sex-atypical (in accordance with their experienced gender), rather than sex-typical (in accordance with their natal sex) hypothalamic activations during olfactory stimulation with androstadienone. We found that the sex difference in responsiveness to androstadienone was already present in pre-pubertal control children and thus likely developed during early perinatal development instead of during sexual maturation. Adolescent girls and boys with GD both responded remarkably like their experienced gender, thus sex-atypical. In contrast, pre-pubertal girls with GD showed neither a typically male nor female hypothalamic activation pattern and pre-pubertal boys with GD had hypothalamic activations in response to androstadienone that were similar to control boys, thus sex-typical. We present here a unique data set of boys and girls diagnosed with GD at two different developmental stages, showing that these children possess certain sex-atypical functional brain characteristics and may have undergone atypical sexual differentiation of the brain.

A pleasant familiar odor influences perceived stress and peripheral nervous system activity during normal aging

Effects of smells on stress have been demonstrated in animals and humans, suggesting that inhaling certain odorants may counteract the negative effects of stress. Because stress plays a key role in cerebral aging, the present study set out to examine whether positive odor effects on perceived stress can be achieved in elderly individuals. To this end, two groups of aged individuals (n = 36 women, aged from 55 to 65 years), were tested. The first group was exposed for 5 days to a pleasant and, by end of exposure, familiar odor (“exposure odor”), whereas the other was exposed to a non-scented control stimulus. Stress and mood states were assessed before and after the 5-day odor exposure period. Psychophysiological markers were also assessed at the end of exposure, in response to the “exposure odor” and to a “new odor.” Results revealed that stress on this second exposure was decreased and zygomatic electromyogram activity was increased specifically in the group previously exposed to the odor (p < 0.05). Taken as a whole, these findings offer a new look at the relationship between perceived stress, olfaction and normal aging, opening up new research perspectives on the effect of olfaction on quality of life and well-being in aged individuals.

Adding odor: Less distress and enhanced attention for 6-month-olds

The effect of odor on cognitive and emotional processes has been studied in adults and children, but less so in infants. In this study twenty-seven six-month-olds were presented with a video while in either an odor (pine or baby-powder) or a no odor control condition. The video was a 92-s audiovisual presentation of a woman expressing happiness and sadness, with the order of emotion counterbalanced. Infant attention (looking time) and emotional expression (smiling, crying, mouthing) were coded. Infants looked longer in the presence of odor and expressed less crying and mouthing but more smiling behavior. Presence of odor markedly reduced infant emotional distress and increased attention, suggesting that the olfactory sensory system provides cues to infants that support mood regulation and maintain attention. These results have implications for optimizing infant environments for emotional health and cognitive development.

Expression of corticosteroid binding globulin in the rat olfactory system

Glucocorticoids are known to act on the olfactory system although their mode of action is still unclear since nuclear glucocorticoid receptors are mostly absent in the olfactory mucosa. In this study we used immunocytochemistry, in situ hybridization, and RT-PCR to study the expression and distribution of corticosteroid binding globulin (CBG) in the rat olfactory system. Mucosal goblet cells could be immunostained for CBG. Nasal secretion contained measurable amounts of CBG suggesting that CBG is liberated. CBG immunoreactivity was localized in many of the basal cells of the olfactory mucosa, while mature sensory cells contained CBG only in processes as determined by double immunostaining with the olfactory marker protein OMP. This staining was most pronounced in the vomeronasal organ (VNO). The appearance of CBG in the non-sensory and sensory parts of the VNO and in nerve terminals in the accessory bulb indicated axonal transport. Portions of the periglomerular cells, the mitral cells and the tufted cells were also CBG positive. CBG encoding transcripts were confirmed by RT-PCR in homogenates of the olfactory mucosa and VNO. Olfactory CBG may be significant for uptake, accumulation and transport of glucocorticoids, including aerosolic cortisol.

Chemosignals, hormones and mammalian reproduction

Many mammalian species use chemosignals to coordinate reproduction by altering the physiology and behavior of both sexes. Chemosignals prime reproductive physiology so that individuals become sexually mature and active at times when mating is most probable and suppress it when it is not. Once in reproductive condition, odors produced and deposited by both males and females are used to find and select individuals for mating. The production, dissemination and appropriate responses to these cues are modulated heavily by organizational and activational effects of gonadal sex steroids and thereby intrinsically link chemical communication to the broader reproductive context. Many compounds have been identified as "pheromones" but very few have met the expectations of that term: a unitary, species-typical substance that is both necessary and sufficient for an experience-independent behavioral or physiological response. In contrast, most responses to chemosignals are dependent or heavily modulated by experience, either in adulthood or during development. Mechanistically, chemosignals are perceived by both main and accessory (vomeronasal) olfactory systems with the importance of each system tied strongly to the nature of the stimulus rather than to the response. In the central nervous system, the vast majority of responses to chemosignals are mediated by cortical and medial amygdala connections with hypothalamic and other forebrain structures. Despite the importance of chemosignals in mammals, many details of chemical communication differ even among closely related species and defy clear categorization. Although generating much research and public interest, strong evidence for the existence of a robust chemical communication among humans is lacking.

Sex discriminations made on the basis of ambiguous visual cues can be affected by the presence of an olfactory cue

BACKGROUND

Almost every interpersonal interaction is mediated by the sex of the individuals involved. Visual, auditory, and olfactory cues provide individuals with the opportunity to discriminate the sex of others from a distance and so prepare sex-appropriate behaviours for any impending interaction. The usefulness of that important social skill is mediated by the reliability of the sensory information. Sometimes cues in one domain will be ambiguous, and the perceptual processes mediating sex perceptions will need to integrate information from across the senses for better reliability. With that in mind, the experiment reported here was designed to explore the effect of olfactory-visual interactions on sex perceptions.

METHODS

Observers were presented visually with point-light walkers that were sexually ambiguous (not unequivocally female or male). They were asked to judge, using a two-alternative forced choice paradigm, the sex of each walker. Tested on two occasions, observers unknowingly made sex judgements in the presence or absence of pads soaked in male sweat.

RESULTS

The presence of male sweat was associated with higher proportions of 'male' judgements of both ambiguous female and ambiguous male walkers (F1,19 = 24.11, p < 0.01).

CONCLUSION

These findings suggest that olfactory cues can modulate visual sex discriminations made on the basis of biological motion cues. Importantly, they seem to do so even when the olfactory cue is not consciously perceived, suggesting these effects are mediated by perceptual rather than cognitive processes. These findings suggest that there exist cortical processes mediating sex perceptions that are capable of integrating visual and olfactory information. What is important is that this sensory integration takes place without conscious knowledge and that appropriate behaviour modifications may occur automatically.

Heterosexual men and women both show a hypothalamic response to the chemo-signal androstadienone

The odorous steroid compound 4,16-androstadien-3-one (androstadienone), found in axillary sweat, was previously reported to evoke hypothalamic activation in heterosexual women, but not in heterosexual men. However, subjects were exposed to the pure crystalline form of androstadienone, which raised the question whether the observed hypothalamic response is physiologically relevant. Therefore, in the present study, we asked whether sexually dimorphic hypothalamic responses could be measured when subjects were exposed to lower, more physiologically relevant concentrations of androstadienone. A total of 21 women and 16 men, all heterosexual, participated in our functional magnetic resonance imaging study (fMRI). Three different concentrations of androstadienone diluted in propylene glycol (10 mM “high,” 0.1 mM “medium” and 0.001 mM “low”) were delivered to the subjects’ nostrils using a computer-controlled stimulator. When exposed to the “high” androstadienone concentration, women showed stronger hypothalamic activation than men. By contrast, men showed more hypothalamic activation when exposed to the “medium” androstadienone concentrations in comparison to women. Thus, we replicated that smelling the chemo-signal androstadienone elicits a hypothalamic activation. However, this effect does not seem to be gender-specific, because androstadienone activated the hypothalamus in both men and women, suggesting that androstadienone exerts specific effects in heterosexual individuals of both sexes.

Androstadienone in Motor Reactions of Men and Women toward Angry Faces

The endogenous compound androstadienone modulating the evaluation of others and activating the human fear system was hypothesized in terms of processing socially relevant cues by regulating responses to angry faces. Androstadienone was investigated in association with arm movements of 62 participants (30 women) in response to happy and angry facial expressions. Volunteers pushed away or pulled toward them a joystick as fast as possible on seeing either an angry or a happy cartoon face on a computer screen. This task was repeated twice: once during exposure to androstadienone masked with clove oil and once to clove oil only. In the former condition participants' reaction speed was accelerated, especially when reacting to angry faces. This observation may indicate an androstadienone-related activation of the fear system leading to faster responses to threat signals, assuming an enhanced allocation of attentional resources toward threat-related social cues.

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 critical for conception. These findings offer a substantial contribution to the current debate about the effects that subliminally perceived body odors might have on behavior.

Heteronormative pheromones? A feminist approach to human chemical communication

I analyse scientific articles on human pheromones from a critical feminist perspective, using new materialist feminist theories, in particular, the work of Judith Butler, Karen Barad and Annemarie Mol. Pheromones were defined by Karlson and Lüscher in 1959 as ‘substances which are secreted to the outside by an individual and received by a second individual of the same species, in which they release a specific reaction – for example, a definite behavior or a developmental process’. In humans, it remains unclear whether substances act as pheromones. With reference to Butler, I show how heteronormativity as a discourse influences research on two potential human pheromones, androstadienone and estratetraenol. I argue that experiments on these two substances have been set up to combine sex-specificity, heterosexuality and reproduction. In these experiments, only the inconsistent effects of androstadienone and estratetraenol were demonstrated. With reference to Barad, I interpret this inconsistency as an indicator of ‘resistant matter’. I argue that in order to experimentally show ‘heteronormative pheromones’ materialities (pheromones) have to merge with discourse (heteronormativity). Androstadienone and estratetraenol partly refuse this collaboration. Finally, I refer to Mol's concept of multiple realities and discuss whether alternative, non-heteronormative effects of pheromones occur instead.

The vomeronasal organ is not involved in the perception of endogenous odors

Chemosensory-based communication is a vital signaling tool in most species, and evidence has recently emerged in support of the notion that humans also use social chemosignals (so-called pheromones) to communicate. An ongoing controversy does exist, however, concerning the receptor organ through which these chemicals are processed. There is a widespread belief that the vomeronasal organ (VNO) is responsible for processing social chemosignals in humans. Here we demonstrate that functional occlusion of the VNO does not change the percept of, sensitivity toward, or functional neuronal processing of a putative human pheromone. Perithreshold and suprathreshold perception of the endogenous chemical androstadienone (AND) were compared, as were positron emission tomography brain activations evoked by AND when the VNO was either occluded or left open. In addition, we compared sensitivity to AND in subjects with an identifiable VNO to those in whom no VNO could be detected. Thus we could examine the effects of the VNO at several different levels of processing. Occlusion or absence of the VNO did not affect either the perceptual measurements or the functional processing of the putative human pheromone, AND. These results provide strong evidence that the human VNO has no obvious function. Pheromonal communication in humans may be conveyed via the main olfactory system.

Sexual dimorphism in olfactory signaling

What makes males and females behave differently? Although genetic master-regulators commonly underlie physical differences, sexually dimorphic behavior is additionally influenced by sensory input such as olfactory cues. Olfaction requires both ligands for signaling and sensory neural circuits for detection. Specialized subsets of each interact to generate gender-dimorphic behavior. It has long been accepted that males and females emit sex-specific odor compounds that function as pheromones to promote stereotypic behavior. Significant advances have now been made in purifying and isolating several of these sex-specific olfactory ligands. In contrast, the neural mechanisms that enable a gender-dimorphic response to these odors remain largely unknown. However, first progress has been made in identifying components of sexually dimorphic olfactory circuits in both Drosophila and the mouse.

Psychological and physiological evaluation of emotional effects of a perfume in menopausal women

In the present study, we familiarized menopausal women with a pleasant smell in the skin care products, they used for 1 week and assessed whether their mood and emotions improved using behavioural and physiological tools. Eventually, we studied the effects of inhaling the familiar fragrance on physiological response of the subjects. An anhedonia questionnaire was used to distinguish the effects of the test products according to low vs. high score of anhedonia. Familiarization with the fragrance induced a modification of some physiological parameters, reflecting a relaxing effect, and these unconscious effects paralleled the conscious positive effects on mood recorded during the familiarization phase; it appeared that the effects were more prominent in subjects with higher scores of anhedonia. These results suggest that the pleasant smell of a skin care product contributes to the quality of life in a population of menopausal women with low easiness to experience pleasure.

Male axillary extracts modify the affinity of the platelet serotonin transporter and impulsiveness in women

The presence of functional pheromones in axillary extracts in humans is still matter of debate. Scattered data suggest that unidentified human axillary compounds with pheromonal activity may influence mood and this may occur, perhaps, through the modulation of the serotonin (5-HT) system that has been linked to mood by several findings. Therefore, the aim of this study was to assess the possible changes of a peripheral marker of the 5-HT system, i.e., the platelet 5HT transporter, and of some psychological tests, in a group of women who were exposed to male axillary extracts (group 1). A matched group of women who underwent an exposure to a neutral solution, were used as control subjects (group 2). The 5-HT transporter was evaluated by means of the specific binding of (3)H-paroxetine ((3)H-Par) to platelet membranes, as well as by means of (3)H-5-HT reuptake in whole platelets, at baseline (T0) and 1h after the stimulation (T1). The following tests were used: the "Experiences in Close Relationships" questionnaire (ECR), the latest version of the Barratt Impulsiveness Scale (BIS-11) and the Structured Clinical Interview for Mood Spectrum, self-reported version. The dissociation constant (Kd) of (3)H-Par binding showed a significant decrease at T1 only in the women exposed to male axillary extracts, as compared with baseline values, while the Bmax and (3)H-5-HT reuptake parameters did not show any change in both groups. The correlation analyses showed that at T0, the Kd values correlated significantly and positively with the factor of motor impulsiveness in all subjects. Two factors of the BIS-11, in particular, the attentional and the motor impulsiveness were significantly lower at T1 in the group 1. Further, at T1 and still in the group 1, a significant and positive correlation was measured between the Kd values and two ECR attachment styles, the secure and preoccupied, as well as with the ECR anxiety scale. Taken together, these findings suggest that the application of male axillary extracts to women may modify the affinity of their platelet 5-HT transporter, as well as of some impulsiveness and romantic attachment characteristics. The substances responsible for this effect remain to be identified.

Female perception of male body odor

Olfaction is one of the most crucial forms of communication among nonhuman animals. Historically, olfaction has been perceived as being of limited importance for humans, but recent research has documented that not only do humans have sensitive olfactory abilities, but also odors have the potential to influence our physiology and behavior. This chapter reviews research on olfactory communication among humans, focusing on the effects of male bodily odors on female physiology and behavior. The process of body odor production and the detection of olfactory signals are reviewed, focusing on potential sex differences in these abilities. The effects of male body odors on female physiological and behavioral effects of body odors are considered. Finally, with specific regard to female mate choice, evidence regarding the influence of the major histocompatibility complex and fluctuating asymmetry on male olfactory cues is reviewed.

Current issues in the study of androstenes in human chemosignaling

We review research on the 16-androstenes and their special claim, born originally of the finding that androstenes function as boar pheromones, to be human chemosignals. Microbial fauna in human axillae act upon the 16-androstenes to produce odorous volatiles. Both individual variation and sex differences in perception of these odors suggest that they may play a role in mediating social behavior, and there is now much evidence that they modulate changes in interpersonal perception, and individual mood, behavior, and physiology. Many of these changes are sensitive to the context in which the compounds are experienced. However, many key outstanding questions remain. These include identification of the key active compounds, better quantification of naturally occurring concentrations and understanding how experimentally administered concentrations elicit realistic effects, and elucidation of individual differences (e.g., sex differences) in production rates. Until such issues are addressed, the question of whether the androstenes play a special role in human interactions will remain unresolved.

Corrugator muscle responses are associated with individual differences in positivity-negativity bias

Corrugator supercilii muscle activity is considered an objective measure of valence because it increases in response to negatively valenced facial expressions (angry) and decreases to positive expressions (happy). The authors sought to determine if corrugator activity could be used as an objective measure of positivity-negativity bias. The authors recorded corrugator responses as participants rated angry, happy, and surprised faces as "positive" or "negative." The critical measure of bias was the percentage of positive versus negative ratings assigned to surprised faces by each participant. Reaction times for surprise expressions were longer than for happy and angry expressions, consistent with their ambiguous valence. Participants who tended to rate surprised faces as negative showed increased corrugator activity to surprised faces, whereas those who tended to rate surprise as positive showed decreased activity. Critically, corrugator responses reflected the participants' bias (i.e., their tendency to rate surprise as positive or negative). These data show that surprised faces constitute a useful tool for assessing individual differences in positivity-negativity bias, and that corrugator activity can objectively reflect this bias.

A dual physiological character for sexual function: libido and sexual pheromones

Human sexual response is a complex function involving many cerebral, spinal and peripheral aspects; the last are relatively known and benefit from good pharmacological control, as in the case of erectile dysfunction. Spinal cord sexual reflexes also have a good theoretical and experimental description. There is minimal understanding of the cerebral sexual processes (libido, sexual arousal, orgasm). The initial perspective was that the cerebral areas implied in sexuality exert descending stimulatory and inhibitory influences on spinal cord sexual centres/reflexes. This was a wrong supposition, which inhibited progress in this subject, with a considerable impact on a subject's individual and social life. A new approach to sexual function arises from the idea that simple neurological structures can support only simple functions, while a more complex function requires correspondingly complex anatomical structures. For this reason the spinal cord would not be able to realise the integration of multiple (spinal and psychosensorial) stimuli into a unique and coherent ejaculation response. Consequently, all mechanisms implied in human sexuality would be cerebral processes, ejaculation reflexes ascending in evolution to the cerebral level. This new evolutionary concept was developed after 2001 in five distinct articles on the cerebral duality of sexual arousal, sexual hormones, ejaculation and serotonergic receptors. During this period other published results suggested a possible cerebral duality for sexual pheromones and libido in humans. All these dual physiological aspects are integrated in this review into one neurophysiological model, thus trying to further develop the new concepts of sexual function and perhaps relational behaviour. In conclusion, ejaculation is a dual cerebral process with arousal sensation (hormonally modulated) and libido perception (pheromonally modulated) as the afferent part. Two neurophysiological axes could exist in both men and women. In this assumption the mechanisms for libido and sexual arousal are not the only ones invoked, their correlations and implications are also suggested, perhaps critical aspects for further developments in the field.

Putative human pheromone androstadienone attunes the mind specifically to emotional information

The putative human pheromone Delta4,16-androstadien-3-one (androstadienone), a non-androgenic steroid found in sweat and saliva, modulates psychological, physiological and hormonal responses without detection as an odor. To determine the specific psychological processes altered by androstadienone, four studies were completed by 50 men and women after solutions of 250 microM androstadienone or clove-odor control carrier, on separate days, were applied to their upper lip: (1) face pairs were subliminally presented, with one face neutral and the other happy or angry. Androstadienone accelerated speed to locate a subsequent dot probe appearing on the same side as emotional faces, without affecting overall reaction times, indicating that androstadienone specifically enhanced automatic attention to emotional information. (2) In two Stroop paradigms, emotional or mismatched color words interfered with ink color identification. Androstadienone slowed ink color identification of emotional words, demonstrating greater allocation of attentional resources towards emotional information, with no effect on the cognitive Stroop. (3) To test effects on social cognition, participants performed two working memory tasks with distinct stimuli, neutral faces or shapes. Androstadienone did not alter attention to either the social or nonsocial images. (4) The ameliorative effects of androstadienone on self-reported attentiveness were replicated, consistent with increased attention to emotional visual stimuli. Moreover, androstadienone did not alter positive or negative mood, as participants were alone during testing, which removed emotional stimuli from social interactions with a tester. Taken together, these findings demonstrate that subliminal androstadienone guides psychological resources to specifically engage stimuli with emotional significance and does not alter attention to social or general cognitive information.

The amelioration of olfactory acuity upon sexual maturation might affect food preferences

Upon sexual maturation, olfactory acuity in women ameliorates and starts oscillating across the cycle. During ovulation, mean olfactory threshold is 30 times lower than during bleeding. Interestingly, menstruated women undergo maleodorant trimethylaminuria. We argued that olfactory amelioration during ovulation might concur to a mating strategy, whereas olfactory impairment during bleeding might protect women against self-refusal. Testosterone and its 17β-estradiol derivative might be responsible for the synchronization of these menstrual events. Furthermore, we posed the question whether olfactory detection amelioration upon sexual maturation might provoke a change in food preferences, for instance a reduction in fish consumption. A preliminary survey in Italy provided encouraging results: 15-44 year-old women have lower fish consumption than 3-14 year-old girls. Surprisingly, men exhibited the same behaviour, so new olfactory tests as well as testosterone measurements are under way.

Repetitive olfactory exposure to the biologically significant steroid androstadienone causes a hedonic shift and gender dimorphic changes in olfactory-evoked potentials

The function of a sensory system is to transduce and relay sensory information in a constant and reproducible manner. However, in the olfactory processing of certain steroids this precept of sensory constancy does not appear to apply. Using threshold testing, psychometrics, and electrophysiological techniques, we investigated the effects of a repetitive exposure protocol on the response to androstadienone. Androstadienone is a steroid found in human secretions that has been widely proposed as a candidate for a human pheromone. The detection threshold, hedonic perception, and evoked potential response all changed following repetitive exposure to androstadienone and not to a control odorant, benzaldehyde. Furthermore, the exposure-dependent changes in evoked potentials exhibited a gender dimorphism in which there were changes in the later components of the evoked potentials specific to women. These components have been associated with cognitive and perceptual operations. This 'learning' to smell a compound found in sweat may be related to biological signaling.

Smelling a single component of male sweat alters levels of cortisol in women

Rodents use chemosignals to alter endocrine balance in conspecifics. Although responses to human sweat suggest a similar mechanism in humans, no particular component of human sweat capable of altering endocrine balance in conspecifics has yet been isolated and identified. Here, we measured salivary levels of the hormone cortisol in women after smelling pure androstadienone (4,16-androstadien-3-one), a molecule present in the sweat of men that has been suggested as a chemosignal in humans. We found that merely smelling androstadienone maintained significantly higher levels of the hormone cortisol in women. These results suggest that, like rodents, humans can influence the hormonal balance of conspecifics through chemosignals. Critically, this study identified a single component of sweat, androstadienone, as capable of exerting such influence. This result points to a potential role for synthetic human chemosignals in clinical applications.

Social odours, sexual arousal and pairbonding in primates

We describe the role of social odours in sexual arousal and maintaining pairbonds in biparental and cooperatively breeding primates. Social odours are complex chemical mixtures produced by an organism that can simultaneously provide information about species, kinship, sex, individuality and reproductive state. They are long lasting and have advantages over other modalities. Both sexes are sensitive to changes in odours over the reproductive cycle and experimental disruption of signals can lead to altered sexual behaviour within a pair. We demonstrate, using functional magnetic resonance imaging (fMRI), that social odours indicating reproductive state directly influence the brain areas responsible for sexual behaviour. Social odours also influence other brain areas typically involved in motivation, memory and decision making, suggesting that these signals have more complex functions in primates than mere sexual arousal. We demonstrate a rapid link between social odours and neuroendocrine responses that are modulated by a male's social status. Recent work on humans shows similar responses to social odours. We conclude with an integration of the importance of social odours on sexual arousal and maintaining pairbonds in socially biparental and cooperatively breeding species, suggesting new research directions to integrate social behaviour, neural activation and neuroendocrine responses.