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Try out PMC Labs and tell us what you think. Learn More. Pheromones are substances which are secreted to the outside by an individual and received by a second individual of the same species. Many examples exist in animals but their role in humans remains uncertain since adults have no functioning vomeronasal organ, which processes pheromone als in animals. Yet pheromones can be detected by the olfactory system although humans under develop and underrate their smelling sense. Pheromones may be present in all bodily secretions but most attention has been geared toward axillary sweat which contains the odorous androstenes.
One of these steroidal compounds, androstadienone, is present at much higher concentrations in male sweat and can be detected by women, albeit with wide variation in sensitivity. Upper-lip application of a pharmacological dose of androstadienonein women in improved mood and heightened focus - particularly to capture emotional information. Indeed, some studies showed a beneficial effect of androstadienone on sexual desire and arousal. However, these effects were dependent on the context of the experiment, for example, on the presence of a male attendant.
Preliminary evidence suggests that exposure to androstadienone in women promotes attractiveness ratings of potential mates. The senses play a pivotal role in the sexual response of women. Bancroft et al. In their model, tactile stimuli give excitatory or inhibitory input to the spinal cord, thereby mediating the genital arousal response. Yet the other senses are also important. While tactile interaction outside a one-to-one relationship is frowned upon, no one in our image-obsessed world doubts the role of visual stimuli in the sexual response.
Auditory stimuli, if less evident eg, lounge music? But what about olfactory stimuli? While most people would agree that unpleasant smells can be strong inhibitory als in the Bancroft sense , it is unclear whether olfactory cues can act as excitatory sexual input. Over time, four types of pheromones have been postulated Table 1. Releaser pheromones often prompt an immediate behavioral reaction, and have received the greatest attention in animals. They are also important for mate selection. Modulator pheromones influence neuropsychological parameters. While these effects are difficult to gauge in animals, they are the focus of most human studies.
Finally, primer pheromones affect neuro -endocrine parameters, including the menstrual cycle. Since endocrine changes generally modulate neuropsychological parameters, modulator and primer pheromones likely overlap.
Pheromones in humans may be present in bodily secretions such as urine, semen or vaginal secretions, breast milk and potentially also saliva and breath, yet most attention thus far has been directed toward axillary sweat. The axillary secretions originate from the highly dense eccrine and apocrine which secrete into hair follicles sweat glands and sebaceous glands. The secretions are odorless but apocrine sweat acquires odor after interaction with the cutaneous bacterial microflora. The main components of sweat are simple organic acids eg, Emethylhexenoic acid and 3-methylhydroxylhexanoic acid Hays, Of these steroids, androstadienone appears to have the most robust effects upon both sexes but particularly upon women Jacob et al.
The concentration of androstenes is much higher in male compared to female axillary sweat. The sex gradient may be the result of the threefold difference in plasma levels as well as different skin flora.
Although these steroids are present at concentrations times below those of some organic acids mentioned ly, their effect ultimately depends on the volatility and the perceptive threshold for these compounds as well as the duration of exposure. A putative pheromone secreted particularly by women is estratetraenol estra-1,3,5 10 ,tetraenol, Fig. This chemoal is likely present in other secretions such as axillary sweat. In general, as we will see, the effects of estratetraenol are smaller than those of androstadienone but go in the same direction.
In small mammals, the presence of a lactating dam within the same cage induces maternal behavior and lengthens the cycle of the non-pregnant females reviewed in Spencer et al. Oxytocin is, of course, the first compound that comes to mind. Oxytocin is readily detected in plasma but is also present, albeit at low concentrations, in urine and saliva Feldman et al. Whether oxytocin is released by olfactory interaction is unknown. Non-human mammals and non-mammal animal species like reptiles and amphibians exhibit a specific tissue that detects most pheromones: the vomeronasal organ VNO , situated in the rostral anterior nasal cavity.
The VNO contains bipolar receptor cells, and its axonal nerve projections traverse the nasal septum and cross the cribriform plate to terminate in the accessory olfactory bulb, adjacent to - yet unconnected with- the main olfactory bulb Fig. While the human fetus shows a VNO with the typical bipolar cells and axonal projections, most evidence shows that it is functionally inactive after birth. Genes coding for receptor proteins are pseudogenes with no protein expression; bipolar receptor cells are no longer detectable, and the accessory olfactory bulb is absent. Interestingly, GnRH-neurons — pivotal for pubertal development and reproduction — replace the degenerated VNO-nerves as they migrate from the fetal VNO-area to the basal forebrain Wysocki and Preti, For example, the sow response to boar androstenone, alluded to above, was still present after the VNO was blocked with surgical cement Dorries et al.
Hence, the absence of a functional VNO in human adults does not preclude pheromone perceptive abilities. Human olfaction is as good as that of other mammals but it is consciously underdeveloped and overwhelmingly rated as the least important sense Sela and Sobel, — people shamelessly gawp and overlisten but most balk at sniffing. Pheromone detection can improve with practice, as was shown for androstenone Wysocki et al. Pheromone solutions are often applied to the skin of study participants. Given that they affect physical parameters including the autonomic nervous system, Bensafi et al.
The study subjects were usually volunteers recruited by posters etc. In the majority of studies, the pheromone and control solutions were applied to the skin between the upper lip and nose on a cotton swab, taped gauze or Q-tip, or they were sniffed from jars. Clearly, the concentration of the pheromone in the test solution was pharmacological in all studies, typically 0. However, adding masking odors to the solution may have affected the study . The pharmacological concentration of the pheromone is not in itself an issue — provided the experiments yield clear and consistent with a convincing P level.
One study examined pheromones released by breastfeeding women using within-brassiere p likely containing spilled milk, apocrine sweat, baby saliva, etc. Recipient women needed to wipe one specimen of both type of p under their noses, each day for 3 months Spencer et al. Such experiments might be considered ethically borderline these days. Several studies with slightly different methodology demonstrated that female participants showed increased positive-stimulated mood affect and reduced negative mood after exposure to either male axillary extracts Preti et al.
The androstadienone-induced mood uplift was dependent on its dose Bensafi et al. A robust reduction in feelings of negative affect and negative character was also found when androstadienone was administered by a vapor pulse directly to the putative VNO Grosser et al. Indeed, studies in a laboratory setting showed that adoption of a positive mood ter Kuile et al. In addition, cognitive distraction during sexual activity is an established predictor of low sexual satisfaction Dove and Wiederman, Perhaps through these psychomechanistic pathways, androstadienone as well as estratetraenol were found to enhance sexual arousal induced by an erotic video Bensafi et al.
Androstadienone also affected biological parameters compatible with increased physical arousal. Activation of the autonomic nervous system produced sympathetic effects in women, cooling their hand palms and increasing their digit skin conductance Jacob et al.
Moreover, salivary cortisol levels were higher after androstadienone exposure compared with vehicle Wyart et al. The brain areas activated by androstadienone are still unclear, with inconsistent across studies Jacob et al. Preliminary data suggest that the brain processing of androstadienone and estratetraenol is different in heterosexual and lesbian women Berglund et al. Importantly, the positive effects of androstadienone on mood and skin conductance Jacob et al.
In contemporary language, the pheromone was interpreted within a given ecological context. Nonetheless, androstadienone also enhanced attention to emotional information in a more recent study which was performed largely without an attendant Hummer and McClintock, In conclusion, the upper-lip application of androstadienone and to a lesser extent estratetraenol was associated with a positive mood and greater focus — in particular to capture emotional information — in women.
However, these effects were dependent on the socioexperimental context. Preliminary studies have suggested some degree of menstrual synchrony after pheromone exposure. For example, in a double-blind experiment, recipient women who daily applied onto their upper lip a donor axillary pad extract, reduced their cycle-day difference with donor women from a mean of 8. In contrast, recipients who applied a blank solution had on average 6.
Yet Strassmann has criticized some studies that purportedly show a role for pheromones in menstrual synchrony Stern and McClintock, She notes that no anthropological evidence for synchrony could be obtained in African communities living close to one another. Menstrual synchrony is no priority when menses are few Kung women in the Kalahari only had a mean of 48 menstrual periods during their lifetime. In conclusion, any potential effects of pheromones on the menstrual cycle need further validation. At the present time, no firm conclusions can be drawn.
Adult humans can identify their own worn T-shirts out of identical shirts worn by others Lord and Kaszprak, Family members can also identify T-shirts belonging to their partners, children and siblings Porter and Moore, ; Wysocki and Preti, Even breastfed infants can identify the axillary pad belonging to their mother — assessed by the duration of orientation of their he toward the pad Cernoch and Porter, Such aler effects may be crucial for partner selection. MHC-heterozygosity is more frequent than expected by chance.The science of pheromones
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What are pheromones and do humans have them?