The hormone oxytocin is a hormone which is produced in the hypothalamus and released by the pituitary gland. It has long been known that the hormone is released during labour and facilitates birth, breastfeeding and initiation of maternal behaviour. Researchers have also investigated the role of oxytocin in pair bonding and social behaviour such as trust. The hormone is sometimes called the "cuddle hormone" because it is related to sexual arousal and bonding in couples. Animal research with prairie voles (Vacek et al. 2002) has found that prairie voles are monogamous. This has been linked to the fact that oxytocin is released into the brain of the female during sexual activity. For the male, it seems that the hormone vasopressin has a similar effect. If secretion of the hormones is blocked during sexual activity the couple will not exhibit the normal behaviour of being monogamous.

Trust is an important social tool that allows humans to form productive and meaningful relationships at a personal and a professional level. However, bonds of trust are fragile and can be disrupted by a single act of betrayal such as an extramarital affair or telling secrets to a third party.

Trust is also important in professional relationships or in business. Researchers such as Baumgarten have been interested in how trust may influence behaviour in economics.

Before reading the study below, you may want to watch this Ted Talk by Paul Zak.

The aim of the study was to investigate the role of oxytocin following breaches of trust.

Baumgarten and his team carried out a study where they used an fMRI to study the role of oxytocin in creating trust between participants during a social game called the "trust game." This game is used by economists and neuroscientists to study social interaction. In a typical trust game, an investor (player 1) must decide whether he or she will keep a sum of money (for example 10 dollars) or share it with a trustee (player 2). If the sum is shared, the investment is tripled (30 dollars). Player 2 (the trustee) now has to decide whether he or she will repay the trust by sharing the gain with player 1 so that each gets 15 dollars or violate the trust by keeping the money. This game is thus built upon the dilemma of either trusting or not trusting. Trusting is profitable but there is also a risk in trusting.

49 participants were placed in an fMRI scanner. They received either oxytocin or a placebo via a nasal spray. Participants were then told to act as investors in several rounds of a trust game with different trustees. In a second condition, they were told that they were going to play a "risk game" with a computer, instead of with another human being.

The participants received feedback from the experimenters in which they were told that their decisions had resulted in poor investment because their trust had been broken. They were then asked to make the next investment decision.

The researchers saw that the feedback had different results. Participants who had received a placebo before they started playing were more likely to decrease their rate of trust after they had been briefed that their trust had been broken. Participants who had received oxytocin in the nasal spray continued to invest at similar rates. Apparently, it did not matter to them that their partner had broken their trust. The researchers could also see different brain areas were active in the two groups. Participants in the oxytocin group showed decreases in responses in the amygdala and caudate nucleus. The amygdala is a structure in the brain involved in emotional processing and fear learning. It has many oxytocin receptors. The caudate nucleus is associated with learning and memory; it plays a role in reward-related responses and learning to trust.

The researchers hypothesized that oxytocin may have a role in decreasing fear reactions (via the amygdala) that may arise as a consequence of betrayal and our reliance on positive feedback that can influence future decisions (via caudate nucleus). It seems that oxytocin may facilitate the expression of trust even after trust has been violated by potentially lowering defence mechanisms associated with social risk. This seems to happen by ignoring the negative feedback, which is important for adapting behaviour in the future. An interesting finding was that the researchers could only observe these behavioural and neural results when participants played the trust game but not when they played the risk game against a computer. According to the researchers, this suggests that oxytocin's effect on trust only comes into play in interactions with real people.

• The study was a highly controlled experiment.  The use of a placebo allows the researcher to infer a cause and effect relationship between the level of oxytocin and the level of trust.
• The use of the fMRI allows the researcher to observe and document activity in the brain during the study. The data can then be verified by other researchers.
• The fMRI is an artificial environment and thus affects the ecological validity of the study.
• Using a nasal spray to increase oxytocin does not reflect natural physiological processes and may not predict what actually happens in a relationship.
• The argument is reductionist.  Sociocultural factors may also affect the degree to which we are able to forgive and continue to trust someone.

In many texts you will read that oxytocin is a hormone that acts as a neurotransmitter in the brain. This means that the hormone may attach to receptor sites of neurons, leading to an inhibitory or excitatory response.  However, this does not mean that oxytocin is a neurotransmitter.  Oxytocin is not released from the terminal buttons of a neuron, but is released through the endocrine system (the hypothalamus and pituitary gland).  It also plays a role in gene expression.

The IB's official position is that students are required to know one neurotransmitter and one hormone for exams.  Credit is not awarded when students write about hormones that "act as neurotransmitters" in order to answer a question on neurotransmitters or neurotransmission.  This strategy leads to zero marks for an SAQ and would lead to low marks for criterion B and C on an essay.