Aggression

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Aggression

Neural and Hormonal causes of aggression

The Limbic System

-The Limbic System (including Hypothalamus and Amygdala) tends to act as an alarm system triggering aggressive response to certain types of threats.

-Giving testosterone to new-born female mice made them act like males with increased aggression, when given testosterone as adults. However, control females only given testosterone as adults did not react in this way (Edwards, 1968).

-This suggests that testosterone masculinises androgen-sensitive neural circuits underlying aggression in the brain.

AO3 Points

  • Research in Greece found that removing the amygdala reduced aggressive incidents by between 33% and 100%, although the sample was small - 13 patients.

  • The Phineas Gage study provides evidence that brain damage may have an effect on personality including aggression.

Serotonin Research

-The PET-1 Gene is linked to the production of the hormone serotonin, which inhibits (i.e. stops) aggression. Damage to the gene, in mice, raises aggression.

-Drugs increasing serotonin production lead to reduced levels of aggression, suggesting that low levels of serotonin are linked to increased aggression.

-Rats selected for reduced aggression levels had higher serotonin and greater levels of serotonin related activity than wild, more aggressive counterparts.

-Research shows a relationship between low levels of serotonin and violent behaviours, suggesting that a lack of serotonin is linked to aggression.

-Lidberg et al (1985) compared serotonin levels of violent criminals with non violent controls, finding the lowest levels of serotonin among violent criminals.

Most evidence linking low levels of serotonin and aggression is only correlational and does not indicate causality.

Testosterone Research

-Giving the hormone testosterone to new-born female mice made them act like males with increased aggression, when given testosterone as adults.

-However, control females only given testosterone as adults did not react in this was, suggesting that testosterone masculinises androgen-sensitive neural circuits underlying aggression in the brain.

-Testosterone affects certain types of aggression in animals, such as intermale aggression as a defence response to intruders, while predatory aggression is not affected (Bermond et al.,1982).

-Van Goozen (1997) conducted a natural experiment on transgender  sex-change patients. This is one of the few cases where research was actually carried out on humans.

-Findings revealed testosterone levels governed aggression. Males receiving testosterone suppressants became less aggressive. Females receiving testosterone became more aggressive.

-Aggressive Boys, violent criminals, military offenders all had high levels of testosterone (Dabbs, 1996).

AO3 Points

  • Individuals with elevated testosterone levels exhibit signs of aggression, but rarely commit aggressive acts, suggesting that social and cognitive factors play a mediating role (Higley et al,1996)

  • Dabbs and Morris (1990) ‘Blocked pathways to success’ study: When a rich boy with high testosterone came home from the army he was less likely to get into trouble, but when a poor boy with high testosterone came home he was more likely to get into trouble.

    • This suggests testosterone doesn’t simply cause aggression, but it makes aggression more likely as a response to frustration.

Cortisol Research

-The fearlessness Theory: Stress, caused by the hormone cortisol may inhibit aggression through fear.

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