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Neurobiology in Human Social Behavior
Introduction
Different individuals expose different but selective social and Sexual attraction behaviors (Mackey, 2003). Individuals acquire these social manners as they grow and develop, and go a long way in determining the individuals conduct, attitude, and choices in life. Sexually, monogamy and bi parenting are still dominant in many societies. The bond between mates of opposite sex tend to be strong and life lasting. (Young and Zuoxin, 2004).
This bond is thought to be biologically designed and dictated by molecular and neural actions. This essay critically analyses two articles that experimentally explain the role of the neuro hormones in bond pair formation. It involves a target essay and a supplementing article. It also relates the articles findings to class work.
Description of the target article
The given target article explores a model study that explains neurological bond pairing. Two neuropeptides, vasopressin and oxytocin, are used in the study. These hormones are made up of proteins, and found in various animals. Oxytocin is a hormone found in mammals. It is produced at the end of the gestation period and causes the relaxation and contraction of the muscles of the uterine wall, leading to parturition. It also boosts milk production in the mammary glands. The two hormones have been considered the main facilitators in recognizing individuals, and especially sexual partners. The study involves the use of these two neuropeptides and dopamine, a hormone thought to be involved in reinforcing the learning process.
Monogamy is widespread in many societies. It is characterized by long enduring relationships, although there are many rodents that exhibit the monogamous sexual behavior. These provide models in studying the biology of pair bond formation. In a monogamous relationship, one male and one female exclusively mate with each other (Pitkou et al, 2001). At times though, extra pair copulation does occur in a monogamous set up.
This is however rare. In this article, the term monogamy has been used to refer to a sexual relationship whereby, the female and male forming a mating pair have exclusive copulation and affection traits towards each other, sharing the nest, and bringing up the offspring together, also known as bi parenting. The mammals of the Microtus genus display the above-mentioned characteristics, and hence ideal for the study of bond pair formation in human beings. The study aims at understanding the human social behavior as well as the human social brain. The Microtus voles species is used in the article.
A laboratory test employs the method of partner preference test, which takes three hours. The test involves three animals, which are; the subject-which already has a mating partner, the mating partner and a novel stranger to the subject. The stranger and the mate are locked up in chambers while the subject is left free. The subject has often been found to spend more time in proximity of the chamber in which the mate is locked up, implying partner preference. Arginine vasopressin and oxytocin are said to be the cause of this partner preference. Oxytocin is also said to facilitate mother- infant regulation, while the vasopressin is associated with male social behaviors.
According to studies, the receptor density of the two hormones is equal in both men and women. There is no explanation yet, as to why the response to the hormones is varied in both sexes. Several hypotheses have however been put forward in an attempt to explain this thought. This has been elaborated below. It has been argued that, introduction of synthetic oxytocin in the cerebral ventricle of females decrease the duration for pair bonding. Administration of the arginine vasopressin in males also reduces the time taken for bond pair formation. Selective receptor antagonists of the two neuropeptides have been said to prevent bond pair formation in both.
The neuropeptides mentioned above also interact with other elements in the neuro transmission system. (Lim and Young, 2004). Monogamous spp. are said to have a higher density of oxytocin receptors in the brain, which involves bond pair formation. These receptors include the nucleus acumens and the caudate putamen. Higher densities of V1aR are found in the ventral palladium and medial dorsal thalamus. Introduction of the oxytocin receptor antagonist in the pre frontal cortex of females affect bond pair formation induced by mating. When the V1aR is blocked in the male before mating in the ventral palladium, bonding pair formation is also affected.
This therefore implies that, the mentioned parts are important parts of the brain involved in bond pair formation. Incidentally, these parts have also been found to be vital in mesolimbic dopamine reward system. For that reason, bonding pair formation and the dopamine reward system use the same circuit.
The reward system makes use of dopamine and is mediated by the dopamine neurons. These have been found to project from the nucleus frontal and cortex accumbency. The ventral palladium relays stimuli, which reward responses such as mating. Bond pairing is thus conditionally learnt, and dopamine appears to regulate this. Injection of a non-selective r dopamine receptor antagonist blocks partner preference, which is induced by mating.
An agonist of dopamine facilitates preference of partner without mating. Dopamine turnover in the nucleus accumbency is increased through mating. Sexual conditioning is dependent on D1 and D2 dopamine receptor types, and their activation. These are found at the nucleus accumbency. Mating is thus a rewarding response. Pair bonding is hypothesized to be an association between unconditioned and conditioned stimuli. Reinforcing properties of sex form the unconditioned stimulus, while the specific olfactory signature of the partner forms the conditioned stimulus.
Studies in the sexual behaviors of human beings have provided evidence of neuropeptide circuits involvement and the rewarding reinforcement during the formation of a bonding pair. Nipple stimulation induces the release of oxytocin which is involved in social attachment. This serves to reinforce sexual bonding as an aspect of sexual activity. Brain activity patterns of individuals in romantic love reveal similar patterns (Nair and Young, 2006).
An experimental article
An experimental article was found to supplement this target article. This is entitled vasopressin and pair bond formation: genes to brain to behavior. In this article, Microtone rodents were chosen because of their monogamous behavior. The study was meant to reveal the vasopressin receptor-binding pattern in the brain and also explain how the pattern affects human behavior. Microtone rodents are also used as models to study social bonding behavior, due to their monogamous behavior found amongst many societies. In this article, a male vole was allowed to cohabit with its partner for 24 hours before the test.
The male was then put in a chamber that was between the partners chamber and the strangers chamber. If the male would spend more time near the chamber with the partner, then, selective partner preference would have been developed. In this article, over 90% of the voles used were found to have developed the selective preference. According to the articles findings, the male rejected the unfamiliar female. It can therefore be concluded that, mating facilitates preferential partner selection in both males and females (Mackey, 2003).
The article describes vasopressin and oxytocin as social bond molecules. The two are brain neurotransmitters. They are synthesized by cells in the brain, and their receptors are also widely spread in the brain. Oxytocin is involved in regulation of social behavior, and particularly the attachment of the infant to the mother. Arginine vasopressin regulates scent marking, aggression, and paternal care (Young &Zuoxin, 2004).
According to the article, the two brain neurotransmitters were found to regulate bond pair formation. Infusion of AVP centrally was found to induce the pair bond formation in males, while oxytocin induced in females. The introduction of their antagonists prevented bond pairing. The difference in response of the two hormones is attributed to the differential location of the receptors in the brain. The variant distribution patterns between species accounts for the differences in social behaviors among the species (Pitkou et al, 2001). The ventral palladium was found to have most of the AVR receptors.
As a result, it is this region that shows the least variation in the many related species of the voles. According to the experiment, over-expression of the AVR receptors at the ventral palladium leads to the expression of preferential selection of a mate. This could be hindered by introduction of D2 dopamine receptor antagonist. This implies that, the pair formation is reward related and depends on dopamine signaling in the ventral palladium, which is regulated by vasopressin (Nair & Young, 2006).
In summary the findings of this article were: males are likely to reject strange females, and that the neuro chemicals oxytocin and arginine vasopressin are social bonding molecules. The two hormones work together with dopamine in the rewarding/ reinforcement system.
These findings imply that, the strong and intense social relations between mates are a biological aspect. Oxytocin has greater effects on the females, while the arginine vasopressin has social effects in the males, giving them the ability to scent partners as well as paternal qualities. Dopamine causes rewarding and reinforces the sexual life.
A critical Approach to the Articles
These articles do not seem to satisfactorily explain the involvement of the neuro hormones in bond pairing and preferential mate selection. They also fail to account for the big percentage of the monogamous male voles mating with multiple females. Moreover, the articles do not explain why there is variation in the ability to form and sustain the bonds (Mackey, 2003). In addition, both articles fail to explain the separation of males from their partners after co-habiting for five days, which leads to the loss of the preferential selectivity in the partner, but retains the identity of the siblings (Lim& Young, 2004).
Social behavior is not only determined by the hormones but other factors too. These may include, early childhood experiences, and stress. This notwithstanding, both articles put more emphases on the neuro hormones aspect, ignoring such factors. The target article ignores the role played by the corticotrophin releasing hormone in relation to anxiety and depression mediation. This hormone has been proven to reconcile emotions which can also affect bond formation (Mackey, 2003).
Conclusion
The neuro hormones, oxytocin and arginine vasopressin, play a great role in determining social behavior. They largely influence the preferential selection of a mate and also lead to formation of strong bonds between mates. However, the hormones are not the only catalysts to such bonding. Nevertheless, studies that seek to explain the unanswered issues relating to preferential mate selection are underway (Pitkou et al, 2001).
Reference List
Lim,M. & Young , J. (2004). Corringendum to vasodepression independent neural circuits underlying pair bond formation. Science direct, vol 128 (issue 1), pg 127-134.
Mackey, W. (2003). Perspectives on human attachment /pair bonding. Evolutionary Psychology, vol 1 (issue1), pg. 138-154.
Nair, H. & Larry, Y.. (2006). Vasopressin and pair bond formation: Genes to brain behavior. Physiology, vol 21, pg. 146-152.
Pitkou, L. et al (2001). Facilitation of affiliation and pair bond formation by vasopressin receptor gene. Journal of neuroscience vol 21 (issue 18), pg. 7392- 78396.
Young, L. & Zuoxin, W. (2004). The neurobiology of pair bonding. Nature neuroscience. Vol 7, pg. 1048-1054.
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