Cortisol Research

What is cortisol in psychology? Cortisol is commonly referred to as the ‘stress hormone’, although it is a steroid hormone with multiple effects across the body and is not purely related to stress. Cortisol functions vary in psychology. It is produced in the cortex of the adrenal glands, regulated by the pituitary gland, which the hypothalamus controls (for hormone release). As part of the glucocorticoid family of steroid hormones, once cortisol is produced, it is released into the bloodstream, where it travels around the body.

Interestingly, almost every cell in the body has a receptor for cortisol. As a result, ensuring cortisol levels remain steady and only fluctuate when necessary is extremely important, as it has a widespread effect on cells and tissues. Too much or too little cortisol is bad for your health if it remains that way for a long time.

• We are going to discuss cortisol psychology research concerning aggression.
• First, we will explore cortisol stress hormone functions.
• Then, we will examine cortisol and aggression and how the two intertwine. Namely, how does cortisol affect behaviour?
• Finally, we will discuss the fearlessness theory and evaluate cortisol research.

Fig. 1: Cortisol is more commonly known as the stress hormone.

Cortisol in Psychology

As we briefly discussed above, cortisol is characterised as a stress hormone with multiple effects on the body. The zona fasciculata of the adrenal cortex produces cortisol. When you are stressed, cortisol is released, and it is implicated in issues with chronic stress. Cortisol is also known for its homeostatic properties.

Let's explore the various functions of cortisol in psychology.

Cortisol Function

Cortisol functions vary across the body. The functions of cortisol include:

• Controlling stress responses in the body.
• Affecting blood sugar levels (more glucose for the brain).
• Regulating metabolism (less energy to digestive systems, more for fight-or-flight response).
• Influencing blood pressure and heart rate.
• Affecting inflammation.

It reacts to stress by inhibiting functions not needed for immediate survival, such as the immune and digestive systems so that the body can focus on the immediate threat.

• It increases your heart rate, narrows your blood vessels, and increases glucose levels, all of which facilitate the body’s ability to ‘fight or flight’. Muscles gain more oxygen and fuel to react.

When your cortisol levels are normal or reacting appropriately to stimuli from your environment, your body can regulate the above functions so that you can navigate the situation appropriately. Your body is usually quite good at bringing hormone levels back to normal after a frightening or stressful situation.

Issues arise with the primitive nature of such responses, however. Stressful situations occur almost every day. They are unavoidable for most people, so the body needs to decide what to do in response to these stressors. Acting aggressively is not always appropriate, nor is being perpetually stressed due to minor inconveniences or issues throughout the day.

Too much or too little cortisol can affect the body negatively.

Cortisol Stress Hormone: How Cortisol Affects Behaviour

How does cortisol affect behaviour as a stress hormone? Cortisol acts as a hormonal modulator of aggression alongside testosterone, and research has indicated the two are linked quite closely when it comes to aggression (Montaya et al., 2012).

According to Dabbs et al. (1991):

Cortisol is an antagonist to testosterone (which usually facilitates aggressive behaviours and impulsiveness). Cortisol is instead an inhibitor of aggression. When cortisol levels are high, testosterone is inhibited, reducing aggressive behaviours in the person.

Similarly, lower cortisol levels have been linked to higher levels of aggression. This link could be due to multiple reasons.

• Testosterone is less inhibited, which means higher levels and higher chances of the amygdala being activated and inducing aggression.

• In Popma et al. (2007), 103 boys aged 13 were referred to a delinquency diversion program.

  • They measured cortisol AND testosterone levels from saliva samples and gave self-report scores on overt and covert levels of aggression.

  • They found a significant interaction between cortisol and aggression concerning overt aggression, with a positive relationship between testosterone and overt aggression in the boys with low cortisol levels but not in the boys with high cortisol levels.

  • Cortisol thus has a moderating effect on testosterone and aggression in male delinquents.

• There may be an interaction with the autonomic nervous system (ANS). Lower levels of cortisol mean the ANS is not as aroused.

Fig. 2: Cortisol has a moderating effect on testosterone and aggression.

Fear, Aggression, and Cortisol

Fear and cortisol levels are somewhat related to their effects on aggression. Cortisol can inhibit aggression through fear responses. Lower cortisol levels mean behaviours are less inhibited, and people will likely act more impulsively.

Consider the study by Goozen et al. (2004). Children with a disruptive behaviour disorder (DBD) show disruptive behaviours, sometimes manifesting in hostility or aggression. Overall, they can be stubborn, difficult, and irritable. They may intentionally violate others and be physically aggressive (Disruptive Behavior Disorders, 2021).

• They tend to have low heart rates, skin conductance and cortisol levels.

• Goozen et al. (2004) compared 21 DBD children to 33 control children. They viewed a series of slides, which were positive, neutral, and negative. Startle probes presented randomly during the presentation also surprised them.

• Researchers also measured eyeblink reflexes.

• Startle-elicited blinks were significantly lower in DBD children for all slides. The more delinquent the DBD children were, the lower their startle response was during negative slides.

• The study suggests a deficit in the DBD’s children fearing modulation capabilities, further suggesting a link between low cortisol levels, disruptive behaviours, antisocial behaviour, and a lack of fear response in these children.

Cortisol Research: Evaluation of Cortisol's Effect on Aggression

It is essential to understand what supports and disagrees with the role of cortisol and how it affects behaviour and aggression.

• Virkkunen (1985): In this study, male violent offenders had their urinary cortisol levels measured while undergoing a mental examination. Participants included 90 male violent offenders and ten male recidivist arsonists versus 20 males with nonviolent antisocial personalities and 15 clinical personnel (male) who acted as controls.

  • Those who were habitually violent offenders with antisocial personalities had low levels of cortisol when compared to other violent offenders, antisocial personalities who did not habitually commit violent crimes, and male clinic personnel.

  • If the offender had a history of a lack of motivation in school, truancy, attention deficit issues and aggressive conduct disorders related to lack of socialisation, they also had low cortisol levels.

  • This study suggests that low cortisol levels could potentially be associated with violent or aggressive behaviours.

• Kruk et al. (2004) conducted five experiments on 53 male rats.

  • They electrically stimulated the rats’ brains, specifically their aggression control centres, to see if this affected their stress hormone levels in the blood.

  • They asked whether these levels were also linked to aggressive behaviours.

  • They found fast, positive feedback between the adrenocortical stress response (which involves your fight or flight mechanisms; your body anticipating action due to stress) and a brain mechanism controlling aggression. Researchers stimulated the aggressive areas of the hypothalamus, activating the adrenocortical response.

  • This response occurred even if the rats were not in a stressful situation, such as if another rat displayed threatening behaviours.

  • A corticosterone injection (synthetic cortisol) in rats with their adrenal glands removed further facilitated hypothalamic aggression. It triggers a release of cortisol as cortisol release activates the hypothalamus, so it is a feedback loop.

  • The feedback loop suggests cortisol contributes to the violent behaviours associated with stressful situations. Stress and aggression work in a positive feedback loop.

• Bokhoven et al. (2005) observed a population-based sample of boys who exhibited aggressive or antisocial behaviours from childhood to adolescence and measured their cortisol levels at 13.

  • Those with conduct disorder (CD), a form of DBD known to be the more physically aggressive subgroup) had higher cortisol levels than boys without CD.

  • Boys with an aggressive form of CD had even higher cortisol levels than those with a less aggressive form of CD.

  • Reactive aggression was associated with higher levels of cortisol.

  • Those with aggressive tendencies in the mentioned subgroups had a more active hypothalamic-pituitary-adrenal system overall, i.e., their hypothalamus stimulated their pituitary gland to release more cortisol, explaining their higher levels.

  • Unlike the other studies, which indicate lower cortisol levels are the reason behind aggression, this one implies the opposite. That’s not to say low levels are still not associated with aggression; rather, high levels of cortisol are also associated with it. Abnormalities in cortisol levels result in a range of issues. It is not as black and white as we first thought. Cortisol plays a vital role in aggression modulation.

• High cortisol levels are associated with social withdrawal, a form of behaviour that has links to aggression.

• However, issues with the above studies exist in the form of reductionism, which reduces it to just a biological explanation. Cortisol is linked to aggression, but human behaviour is ultimately a complex concept, so it is also not a causal link. Many things mediate it, such as:

  • Self-control: Individuals can fine-tune it with practice.

  • Mediating factors: Other hormones, such as serotonin, play a role in aggression and the body.

  • Social learning: What is appropriate and not can mediate aggression, even when the above systems encourage it. Learning to control aggression is effective in children.