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.Also known as hydrocortisone, it is produced in 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.

Cortisol, Flaticon

Cortisol functions include:

• Controlling stress responses in the body.

• Affecting blood sugar levels.

• Regulating metabolism.

• Influencing blood pressure and heart rate

• Affecting inflammation.

It reacts to stress by inhibiting functions not needed for immediate survival, such as the immune system and the digestive system, 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. It would be of no use to you if your heart suddenly started pumping blood rapidly because you were mildly surprised by a dog running past you.

Issues arise with the primitive nature of such responses, however.

Cortisol research: cortisol and aggression

How does cortisol affect behaviour?

Cortisol acts as a hormonal modulator of aggression alongside testosterone, and research has indicated the two steroids are linked quite closely when it comes to aggression (Montaya et al., 2012).

Cortisol acts as an inhibitor of aggression, almost like a modulator compared to testosterone, which usually facilitates aggressive behaviours and impulses. When cortisol levels are high, testosterone is inhibited, which in turn reduces 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 there will be higher levels and higher chances of the amygdala being activated and inducing aggression.

• In Popma et al. (2007), 103 boys aged 13 years old 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.

The fearlessness theory

This theory suggests that the stress cortisol causes can inhibit aggression through fear. Lower levels of cortisol mean behaviours are less inhibited, as mentioned above.

People will likely act more impulsively as a result.

Consider 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 ‘normal’ control children. They viewed a series of slides, which were positive, neutral, and negative. Startle probes presented randomly during the presentation also startled 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 form of deficit in the DBD’s children fearing modulation capabilities, further suggesting a link between the 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 cortisol affects behaviour, and aggression in particular.

• Virkkunen (1985): In this study, male violent offenders measured their urinary cortisol levels while undergoing a mental examination.

  • 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 this. It triggers a release of cortisol as cortisol release activates the hypothalamus, so it is a feedback loop.

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

The feedback loop, Flaticon

• 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 who had an aggressive form of CD had even higher cortisol levels than those who had 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, but rather, high levels of cortisol are also associated with it too. So it is not as black and white as first thought. Cortisol plays a vital role in aggression.

• 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, as it 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 play a role in aggression and the body, such as serotonin.

  • 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.