The Biological Approach to Behavior: Hormones

Hormones are chemical messengers that coordinate different functions in the body. The endocrine system, which is made up of all the body's different hormones, regulates all biological processes in the body, from growth and metabolism to conception and brain development. Hormones, produced by glands, regulate long-term ongoing processes and travel with the blood, unlike neurotransmitters. While hormones do not have a direct influence on behaviour, they do change the probability that a certain behaviour will occur in response to a specific environmental stimulus.

The Endocrine System vs Nervous System

Hormones are released by endocrine glands, which include the following: adrenal glands, hypothalamus, pineal gland, pituitary gland, thyroid, parathyroid, thymus, pancreas, testes and ovaries. Together, these make up the endocrine system.

The endocrine system and the nervous system are both regulatory systems in the body, yet there are a few key differences between them. Firstly, the endocrine system uses chemical signaling (endocrine glands make chemicals called hormones and pass them into the bloodstream) while the nervous system uses electrical signaling. Secondly, neural transmission is relatively fast because neurons are interconnected; however, the functions are much more short-lived. In contrast, signal transmission in the endocrine system is relatively slow, as hormones must travel through the bloodstream; however the responses are generally more long-term.

Despite their differences, it is important to note that the nervous system and endocrine system are interdependent. Meaning that they interact and also influence each other to some extent. Additionally, some chemicals may be both hormones and neurotransmitters, such as, adrenaline.

Introduction to Hormone Function

Hormones are quite similar to neurotransmitters in regards to how they function, this is because both are chemical messengers. However, neural communication and hormonal communication differ in several notable ways.

Hormones are released into the bloodstream and travel with blood to reach their destination. Neurotransmission, on the other hand, is communication along nervous cells. This is important to understand as it implies that hormones can reach places that the nervous system does not cover, because the network of blood vessels is more elaborate. To add on, the nervous system regulates rapid processes such as movement, emotion, decisions, etc. whereas hormones primarily regulate long-term ongoing processes such a growth, metabolism, digestion and reproduction. In general, neural regulation has a higher degree of voluntary control than hormonal regulation. For instance, it is possible for you to control your emotions to a certain extent, whereas the degree of control you have over your growth is negligible. In other words, it easier to control short-term processes than long-term ones.

Target cells, in the endocrine system, are characterised by the presence of certain docking molecules, referred to as receptors, for a specific hormone. When a hormone binds to a receptor, it launches a sequence of changes of which some are genomic. This is known as gene activation or gene suppression. This implies that hormones do not influence behaviour directly, however they do change the probability that a certain behaviour will occur in response to an environmental stimulus.

Over 50 hormones have been identified in humans and other vertebrates. The most well-known hormones include adrenaline, noradrenaline, cortisol, oxytocin, insulin, testosterone and estrogen. However, there is one hormone that is particularly notable in psychology, and that is oxytocin.

Oxytocin - The Love Hormone

Oxytocin, produced in the hypothalamus and released into the blood by the pituitary gland, is a hormone that plays a role in sexual reproduction, childbirth and social bonding. It is commonly referred to as "the love hormone", "the bonding hormone" and "the cuddle chemical". For example, during breastfeeding, oxytocin helps to move milk from the ducts in the breast to the nipple, and helps to establish a stronger bond between the mother and the child. It is also released with every kiss or hug.

Romero et al (2014) demonstrated that oxytocin promotes social bonds in mammals in non-reproductive contexts. In the study, 16 dogs were sprayed intra-nasally. Half were sprayed with oxytocin and the rest were sprayed with a placebo. They were then placed with their owner and another dog in the same room for the duration of one hour. The room was empty except for a chair on which the dog owner sat. The owner was instructed to move the chair in pre-designated positions in ten-minute intervals, but otherwise sit quietly and not actively interact with the dog. The experiment was recorded by four cameras.

The recordings were analyzed after the fact, using a checklist of dog behaviours. This list included sniffing, licking, gentle touching with the nose or paw, play bouts and body contact. Results showed that dogs sprayed with oxytocin showed higher affiliation towards their owner. They also spent significantly more time in close proximity to the owner. This was also the case for the dog partner (the other dog present in the room): affiliation behaviours were more frequent in the oxytocin condition.

Also interesting is that the effect of oxytocin was found to be bidirectional. Blood tests were taken subsequent to the procedure, which showed that the more often the dog interacted with the owner and the dog partner, the higher the levels of endogenous oxytocin it had. Therefore, a conclusion was made that oxytocin triggers social interaction, and social interaction affects the release of more oxytocin.

The Role of Oxytocin in Interpersonal Trust

Kosfeld et al (2005) claimed that oxytocin increases trust in humans. Participants in this study were 128 healthy male students with a mean age of 22 years. They were randomly allocated into either the oxytocin group or placebo group, and substances were administered via an intra-nasal spray.

The researchers designed a trust game with real monetary stakes for the purposes of the experiment. Subjects were paired anonymously and played the role of either an investor or a trustee, Each round of the game, each with a new partner, consisted of three steps.

1. The experimenter gives both the investor and the trustee an endowment of 12 monetary units.
2. The investor is required to decide how much of that to send to the trustee. (There are four options: 0, 4, 8, or 12.) The experimenter then triples whatever is sent to the trustee: for example, if the investor sends 4 units, the trustee would receive 12. Remember that the trustees also have their own endowment, which is added to the total.
3. The trustee decides how much of the now available money to send back to the investor. This is where the "trust" part comes in. If the investor completely trusts the trustee, they would send him 12 monetary units which would turn into 36, and trust that the trustee would send back at least 18 units. However, the investor and trustee only interact once during the experiment, so the temptation of keeping the whole sum is rather great.

Participants played the game four times in the same role, and at the end of the experiment, the total earned monetary units were exchanged for real money.

Results of the experiment showed that the level of trust in the participants who received a dose of oxytocin was higher than in the control group. In the oxytocin group, the median transfer of investors was 10, while in the control group, it was 8. 45% of subjects in the oxytocin group showed the maximum trust level (12 monetary units), whereas only 21% in the placebo group showed the maximum trust level.

To clarify these results, the researchers conducted a follow-up experiment with the same subjects . Only this time, the trust game was one against a random mechanism (software). The algorithm in the software was modelled after decisions of a real people (trustees) in the previous experiments, so the investors faced exactly the same risks as before. However, this time, they knew they were playing against machines. Interestingly enough, no difference was observed between the oxytocin and placebo groups. The median transfer was eight monetary units in both conditions.

Therefore, the researchers concluded that oxytocin specifically affects trust in interpersonal interactions.

Concluding Statements

The study of psychology and the endocrine system is called behavioural endocrinology, which is defined as the scientific study of the interaction between hormones and behaviour. It has long been a topic of interest to psychologists as hormones play an essential role in many biological processes of the human body. They influence many aspects of our body's functions, including metabollism, growth and reproductive system functioning. Our mental health is also strongly impacted by hormones as hormones have a major role to play in the regulation of moods and emotions.

However, the topic of hormones comes with a lot of uncertainty. To what extent do hormones influence behaviour and vice versa? How far does the influence spread? What is the role of hormones in interpersonal relationships? Can we claim that hormones influence some behaviours negatively and some positively?

Many questions are unanswered, but that only means that there is more exploring to be done.