It is known that the neuropeptide oxytocin influences the formation of friendly relations and parental feelings in man. German psychologists recently discovered yet another effect of this very simple peptide structure. It turned out that if you buried him in the nose of men who are in constant monogamous relationship with a woman, then the comfortable distance to an unfamiliar attractive woman for them is significantly increased, which can not be said about men who do not have a permanent partner. Thus, the increase in the endogenous production of oxytocin in married men can serve as a pledge of their adulthood.
In the animal world, not so many species forming monogamous connections are known, and man is one of them. Monogamy is quite an expensive pleasure from the point of view of evolution, as it leads to a significant decrease in the number and genetic diversity of male offspring. On the other hand, for females the benefit is obvious, since in monogamous pairs care for the offspring is borne by both parents. Therefore, it is logical to assume that in the process of evolution mechanisms have been developed that support monogamy.
One of such mechanisms was surprisingly conservative - the regulation of social relations involving neuropeptides oxytocin and vasopressin. The homologues of these neuropeptides are involved in the regulation of relationships already in worms, insects and molluscs. In the prairie voles - rodents known for their matrimonial fidelity - the introduction of oxytocin to females promotes the creation of vapors, whereas the introduction of vasopressin to males turns them into loving husbands. In humans, the most famous function of oxytocin is the regulation of female reproductive function (stimulation of uterine contraction and lactation). Studies with intranasal administration (dripping into the nose) of oxytocin showed that the administration of oxytocin to men increases the level of credulity and the ability to understand the mood of other people, and also to look more at the interlocutor in the eye (see, for example, Genes control behavior and behavior with genes, "Elements ", 12.11.2008). In the past two years, it has been found that oxytocin also affects the establishment of a romantic relationship between a man and a woman. But until recently it was not known whether oxytocin was involved in maintaining monogamous bonds in humans.
A group of German psychologists recently conducted a study on 6 young heterosexual men, half of whom had stable monogamous relationships, and the other half were not in constant communication. In the first experiment, the subjects dripped either oxytocin or placebo into the nose. After that, the subjects were shown an attractive woman and suggested choosing a comfortable distance for them and slightly uncomfortable (Figure Ai). In one case, the woman approached the subject, and he had to stop her, otherwise the subject approached the woman and stopped himself. In addition, it was suggested to assess the degree of attractiveness of the object on a nine-point scale, and also to find out the sensations of the subject (valence, excitement, confusion, rejection, etc.).
In the second experiment, men were also dribbled either oxytocin or placebo, and then presented different pictures on the monitor. As pictures were presented as "positive" images (an attractive woman or a beautiful landscape), and "negative" (distorted picture of a woman or mud). All the images were taken from the photo database used for the study of emotions (IAPS). The pictures were presented in four steps, in each - five images of each type. To select a particular picture, the subjects had to move the joystick either forward or backward. At the same time, the image either increased (imitation of the approach of the object) or decreased (imitation of object removal). The reaction time (the time of the joystick shift) and the number of errors were measured when the joystick shifted in the wrong direction. Subjects also had to evaluate the attractiveness of the object and tell about their feelings.
A series of control experiments was also conducted. In order to ensure that oxytocin influences matrimonial fidelity, rather than, for example, sociability, a separate group of heterosexual men with a permanent partner was offered a man, not a woman, as the object presented in the first experiment.
In order to finally make sure that the woman presented is really attractive for the subjects, they were asked to evaluate her appearance from the photo on a 100-point scale.
The results of the first experiment showed that the optimal distance between a man who is in constant contact with a woman and an object (an attractive woman) is significantly increased after digestion of oxytocin, and this occurs in all situations (that is, regardless of whether the subject or object is moving, whether they are either removed, whether they look into each other s eyes or do not look (Fig. 1Aii, Aiii). In contrast, instillation of oxytocin alone in almost all situations (in seven of eight) did not change the optimal distance. Only when the object approached the subject and looked into his eyes, oxytocin influenced the change in the comfortable distance to the object and in solitary. It is interesting that in all groups of subjects the comfort distance was greater if the subject was leaving the object than if he were approaching it. The authors interpret this result in such a way that the close initial distance is more uncomfortable than the distant initial distance. It also turned out that the differences between men in communication and singles after digestion of oxytocin are stronger if the subject moves, than if the object moves.
As for the slightly uncomfortable distance, it turned out to be greater in men who have a permanent connection, after instilling oxytocin, but only in those cases when the woman moved. At singles slightly uncomfortable distance remained unchanged in all situations. Another authors looked at the connection between the slightly uncomfortable distance and other characteristics of the subjects and found a positive correlation between the uncomfortable distance and the degree of social anxiety (see: Augustine Osman et al., 1998. The Social Phobia and Social Interaction Anxiety Scales: Evaluation of Psychometric Properties). This correlation indicates that the evaluation of slightly uncomfortable distances is a good criterion for reflecting the motivation of the subject to come into contact with a stranger.
In the control experiment with a male, no correlation was found between the different parameters as an object-in other words, the instillation of oxytocin influenced precisely inter-sex relations, and not sociability as such. In another control experiment, the subjects highly appreciated the attractiveness of the woman who participated as an object in the first experiment: she was awarded an average of 64 out of 100 points.
The results of the second experiment showed a reliable relationship between instillation of oxytocin and conjugal bonds only for positive female images (Fig. 1B). After instilling oxytocin, men who have a couple, looking at an attractive woman, thought much more before responding correctly, and made far more mistakes than single people.
So, this study shows that the behavioral effects of oxytocin depend on the context and the presence of a permanent partner. This work is the first direct evidence that oxytocin can change the behavior of married men in such a way as to maintain a monogamous relationship. It is interesting that the questioning of the subjects did not reveal any significant changes in sensations or arousal caused by the appearance of an attractive woman. This means that the effect of oxytocin can not be associated with a conscious attitude toward the object. This statement is also confirmed by the absence of a link between the effect of oxytocin administration and the direction of the glance. One would expect that the optimal distance should increase if the subject and the object are looking into each other’s eyes; but it was not so.
Oxytocin in humans is produced in the hypothalamus and secreted into the blood. Measurement of the concentration of oxytocin in the blood of people of both sexes showed that this concentration rises in the early stage of romantic love and remains elevated during the first 6 months of life together (Schneiderman et al., 2012. Oxytocin during the initial stages of the romantic attachment: relations to couples’ interactive reciprocity). After that, the production of endogenous oxytocin in men as a whole is reduced; it rises only for a short time after the physical proximity of partners and even after a short stay next to each other.
The authors do not urge suspicious wives to drip oxytocin to their husbands who are striving to look to the side (although, perhaps, some readers may perceive this study as a direct guide to action). However, scientists emphasize the need for further studies of the neurochemical mechanism of the effect of oxytocin on behavior, as well as an analysis of other aspects of human relationships that may affect the production of oxytocin. This will undoubtedly bring us closer to a better understanding of the extremely complex and enigmatic neurobiology of the formation of matrimonial relations in man.
Source: Dirk Scheele, Nadine Striepens, Onur Güntürkün, Sandra Deutschländer, Wolfgang Maier, Keith M. Kendrick, René Hurlemann. Oxytocin modulates social distance between males and females. The Journal of Neuroscience. V.32. P. 16074- 16079.