1. Introduction
People experience stress daily. Whether the underlying reason is something trivial/banal such as the long line in a coffee shop, or more serious (loss of a beloved pet), the effect that stress has on a human being’s organism is still negative and needs to be alleviated.
Since the beginning of the 20th century, researchers in neuroscience, psychology, and psychiatry have been investigating the correlation between social support and stress responses in humans. Although these studies have indicated a positive influence of social support on the stress-responsive behaviors, only few of them focused on the biological factors contributing to that phenomenon (Heinrichs et al. 2003). However, now oxytocin, a neuropeptide hormone that is produced in the hypothalamus and is integral in sexual reproduction, is thought to have a crucial role in prosocial behaviors (McQuaid et al. 2016). Following the findings that illustrated oxytocin’s behavioral and physiologic stress-alleviating effects in animals (Heinrichs et al. 2003), scientists assumed that this hormone can also demonstrate the same effect in humans. Indeed, recent experiments point out that one of the important factors that enhance the overall human being’s response to stressors is the level of oxytocin. Taking into consideration the underlying traceable correlation between oxytocin functions and social behaviors, psychologists, neuroscientists, and psychiatrists have begun to investigate the interaction of social support and oxytocin to determine how the hormone can attenuate stress responses, and how social support can moderate oxytocin’s effect on them. In this literature review, I will primarily focus on the types of experiments, participant pool, kinds of social stress triggers that researchers preferred, and reasons that led scientists to choose these particular methods.
2. Brief Experiments’ Description
There were three experiments conducted aimed to investigate the role of oxytocin and social support on human beings’ responses to stressors. In the first experiment (Heinrichs et al. 2003), 37 men were recruited and exposed to the social stress test. They were given either the dose of oxytocin or placebo. The second study (McQuaid et al. 2016) involved only female participants who were also subjected to the stress test but were not administered any hormone. In the third experiment (Linnen et al. 2012), the participant pool included both genders and was exposed to social stress and received either placebo or intranasal oxytocin administration.
3. Methodology
3.1 Types of experiments
All of the researchers (Heinrichs et al. 2003, Linnen et al. 2012, McQuaid et al. 2016) conducted controlled experiments. Only Heinrichs et al. and Linnen et al. ran double-blind, placebo-controlled studies meaning that one group of participants received intranasal administration of oxytocin but the other controlled group got placebo. McQuaid et al, however, examined the effect of acute stressors on endogenous oxytocin levels under ordinary conditions. This group of researchers also decided to meticulously extract oxytocin from blood before conducting any measurements. Such difference in approaches, in turn, led to the slight distinction between used stress controllers, namely McQuaid et al. utilized plasma cortisol levels, whereas Heinrichs et al. and Linnen et al. observed salivary cortisol levels.
3.2 Participants
The participant pool that scientists chose for their studies included adults only. Researchers recruited either male, female or both-gender participants. Heinrich et al and McQuaid et al, employed male and female participants respectively. As for the experiment conducted by Linnen et al, both genders were asked to take part in the research.
Social status of the participant pool also varied. Both Linnen et al. and McQuaid et al. chose undergraduate students as subjects of their study in comparison to Heinrichs et al., who recruited male participants-representatives of various backgrounds.
3.3 Social Stress Triggers
There are two types of social stress triggers that have been used in the experiments: Trier Social Stress Test and Yale Interpersonal Stressor. Trier Social Stress Test, the most widely used trigger in this kind of researches (TSST; Kirschbaum et al 1993), consists of the public speaking task and timed mental arithmetic performed in front of the evaluators who, in case of mistakes, remind a participant about the time making the conditions more stressful (Heinrichs et al 2003). It was used in both Heinrich’s and McQuaid’s experiments. Linnen et al, however, used another laboratory procedure to induce stress in participants, namely Yale Interpersonal Stressor. During this stress-inducing method, participants communicated with the two same-sex confederates who made undergraduates feel excluded and isolated (Linnen et al.2012).
3.4 Motives to use specific methodology
McQuaid et al. decided not to conduct a placebo-controlled experiment because there are multiple studies that have already investigated the effect of intranasal oxytocin administration on stress responses (McQuaid et al 2016). In addition to that, in comparison to other scientists, this group of researchers extracted oxytocin before measuring the hormone since this method is thought to provide more accurate data. (McQuaid et al. 2016).
The difference between McQuaid et al. participant pool and that of other scientists is dictated by the location of the oxytocin in the human body. Since the plasma hormone level is most relevant to women, McQuiad et al. included only female participants. Oxytocin also plays a more important role in women’s reproduction and depends on the estrogen, another women’s hormone (McQuiad et al 2016), which fluctuates during different phases of menstrual cycle. Therefore, in contrast to Heinrichs et al. and Linnen et al., estrogen levels were measured by McQuaid et al. as well.
Because one of the goals of the Linnen et al. team was to compare and contrast the stress responses in men and women and to try to replicate the sex-difference in cortisol response made by Stroud et al. 2002. (Linnen et al. 2012), the participant pool included both genders. For that same reason this group of researchers utilized Yale Interpersonal Stressor as it is thought to provoke higher cortisol response in female (Stroud et al. 2002).
4. Results of the experiments
Although the correlation between oxytocin and social support and their effect on human beings’ stress responses still undergoes continuous investigation, two experiments (Heinrichs et al. and Linnen et al.) indicated that intranasal administration of oxytocin suppressed salivary cortisol levels. Moreover, Heinrichs et al. pointed out that participants who received intranasal administration of oxytocin and were provided support during the laboratory procedure demonstrated the lowest cortisol level. McQuaid et al, however, did not detect any changes in the plasma oxytocin levels in the participant pool suggesting that fluctuations in plasma oxytocin levels may not reinforce the effect of social support.
In addition to that, different types of social stress triggers evoked distinct social stress responses. As for the Heinrichs et al. and McQuiad et al, both groups of scientists observed significant elevations of state anxiety in response to Trier Social Stress Test. Whereas Linnen et al, who utilized Yale Interpersonal Stressor, failed to induce considerable cortisol response. Even so, these scientists proved that YIS causes a more negative response in females rather than males.
5. Conclusions and directions for future research
The literature study showed that the outcomes of the experiments conducted are highly dependent on the kind of the social stress trigger. Therefore, the choice of the stressor should be carefully considered and preferably tested before any laboratory procedures. Considering aforementioned results, it seems reasonable to conclude that Trier Social Stress Test should be used in the further trials since it was able to induce a significant enough incensement of the cortisol level in participants.
In case of investigating the oxytocin effects, it would be prudent to contrast and compare both female and male participants since oxytocin plays a more important role in women’s reproduction and depends on the estrogen, another women’s hormone (McQuiad et al 2016), which fluctuates during different phases of menstrual cycle. An issue that has not been addressed in Linnen et al. study is the level of estrogen. Since self-report of menstrual phase may be unreliable (McQuaid et al. 2016), disregard of the estradiol level can question the accuracy of the results. Thus, more information on women hormone could help us to establish a greater degree of precision.
In future investigations, it would also be valuable not to restrict participant pool only to undergraduate students as two of the experiments have done. (McQuaid et al.2016, Linnen et al. 2012). College students are usually experience a lot of stress daily, therefore their cortisol level measurements may not function as the reliable set of data. Oxytocin and social support effects studies are likely to benefit from including children into the participant pool because if proven to be affective, oxytocin may be used as treatment on the early stages of the antisocial behaviors.