1) Neural and hormonal mechanisms influence aggressive behavior. Low levels of serotonin and high levels of dopamine have been linked to increased aggression. Testosterone has also been correlated with aggression, though the evidence is mixed. 2) Studies manipulating or measuring serotonin and dopamine levels in humans and animals support their role in aggression. However, low serotonin may instead lead to more serotonin receptors in the prefrontal cortex. 3) While some studies found a link between testosterone and aggression, others found no association, and high testosterone is more clearly linked to dominance than aggression. Testosterone supplements have also reduced depression in older males.

1. Biological Explanations of Aggression The role of neural and hormonal mechanisms in aggression. Describe & evaluate how neural & hormonal mechanisms influence aggressive behaviour.

2. Neurotransmitters Aggression linked to the action of Serotonin & Dopamine Low levels of Serotonin High levels of Dopamine

3. Serotonin Normal levels of Serotonin have an inhibitory effect on areas of the brain that are regulated by Serotonin. Low levels are thought to reduce the ability to control aggressive impulses leading to aggressive behaviour.

6. Support for this hypothesis has been found in a number of studies that either measure levels of Serotonin or manipulate levels of Serotonin. After Serotonin has been released it is either reabsorbed by brain cells or broken down by enzymes.

7. This process produces waste products. A sample of cerebrospinal fluid is taken and the level of metabolites is measured.

8. Low levels of metabolites indicate low levels of Serotonin. Studies have found low levels of metabolites in people who have poor impulse control and engage in aggressive behaviour.

9. Some studies deliberately manipulate levels of Serotonin. Mann et al (19900 administerd a drug that reduces levels of Serotonin in the brain to 35 healthy adults. A questionnaire was given to the participants that assessed their levels of hostility and aggression before and after the treatment.

10. This study found that the male participants hostility and aggression rating increased after treatment with the drug. Coccaro & kavoussi (1997) found that aggression was reduced after administering the antidepressant drug Prozac.

12. Evaluation Aggression may not be caused by low levels of serotonin. Problems in serotonin metabolism may lead to the development of more receptor sites in the pre-frontal cortex.

13. Evidence to support this alternative explanation has mainly come from post-mortem studies of the brains of people who have committed suicide. Arora and Meltzer (1989) found that people who had killed themselves using a very violent method had more serotonin receptor sites in the pre-frontal cortex than a control group who had not used violent methods.

14. Mann et al (1996) also found that people who had committed suicide using violent methods had more serotonin receptors in their pre-frontal cortex. The well established link between alcohol and aggression may be due to the effect of alcohol on serotonin. Badawy (2006) found that alcohol reduces serotonin levels. This reduction may lead to the aggressive behaviour observed.

15. Dopamine There is some evidence that there is a link between elevated levels of dopamine and dopamine activity in the brain and an increase in aggressive behaviour.

16. Dopamine agonists that reduce dopamine activity in the brain have been administered to reduce aggresive behaviour. One explanation for the effect of dopamine on aggressive behaviour is linked to the effect of dopamine on reward systems in the brain.

18. Aggressive behaviour may activate the release of dopamine and generate rewarding feelings. This reinforces aggressive behaviour: some people may seek out aggressive situations because it makes them feel good.

19. Evaluation Evidence to support the dual role of serotonin and dopamine has mainly been found in animal studies.

20. Ferrari et al (2003) conducted an experiment that forced rats to fight at exactly the same time every day for 10 days. On the 11th day the rats were not allowed to fight and the level of serotonin and dopamine was measured in their brain. Ferrari found that the rat’s serotonin levels had decreased and their levels of dopamine had increased. This shows that consistent aggressive behaviour had changed the rats brain chemistry.

21. Hormones Hormones are chemicals that regulate and control physiological processes. They also control responses to external threats. The ‘fight-flight’ response is an example of how hormones control responses to external threats.

22. Testosterone has been linked to aggression and aggressive behaviour.

23. Testosterone is produced by males in the testes. Women produce testosterone in the adrenal glands. Testosterone produces male characteristics.

24. Research on the link between testosterone and aggression has mainly involved studies using correlational analysis or the measurement of levels of testosterone between aggressive and non-aggressive people.

26. Archer (1991) conducted a meta-analysis of 5 studies and found a low positive correlation between testosterone and aggression. Brook et al (2001) conducted a meta-analysis of 45 studies and found a mean correlation of + 0.14 between testosterone and aggression.

27. Olweus et al (1980, 1988) took samples of blood and maesured levels of testosterone from delinquent male adolescents and ‘normal’ male students. The researchers found slightly higher levels of testosterone in the delinquent adolescent males than the ‘normal’ male students. However, the difference was not statistically significant.

28. Research suggests that higher levels of testosterone is associated with dominance behaviour rather than aggression. Some types of dominance behaviour may involve aggression but most do not.

29. Evaluation Research has not found a consistent link between testosterone and aggression. A few studies have found a strong positive correlation between high levels of testosterone and high levels of aggression.

30. However, other studies have found no association. Bain et al (1987) found no significant differences in testosterone levels and men convicted of violent and non-violent crimes.

31. Kreuz and Rose (1972) also found no difference in testosterone levels in a group of 21 prisoners who had been classified as violent and non-violent. Furthermore research suggests that testosterone far from causing aggressive behaviour actually has positive health benefits. Levels of testosterone in males decline as they get older.

32. Testosterone supplements have been used successfully to treat age related depression in males. McNicholas et al (2003 ) conducted a study of 208 men who had been treated with testosterone replacement therapy and found statistically significant increases in positive mood and decreases in negative mood. Reduction in levels of testosterone are linked to the development of depression in older males.

33. Read the handout and answer the questions