1. Aggression 2

2. Biological explanations of aggression
Neural and hormonal mechanisms in aggression
Genetic factors in aggressive behaviour

3. The Role of Neural and Hormonal Mechanisms in Aggression
To understand how destroying the amygdala reduces aggression.
Explain how testosterone leads to aggressive behaviour.

4. Is aggression
Nature or nurture?

5. *@!* off, I’ve got a splitting headache!
Phineas Gage
One of the best examples of how brain injury can influence aggressive behaviour is the case of Phineas Gage.
Working on a railway in 1848, he had an accident in which a tamping iron went up through his face , behind his left eye and out through the top of his head.
He survived the accident, but his personality was changed, including a huge increase in aggression.
off, I’ve got a splitting headache!

6. Neural Mechanisms – Brain structure
Normal aggressive behaviour is not dependent on separate brain structures, but interaction of a system of structures.
Amygdala
Hypothalamus
Periaqueductal grey
Organised hierarchically and moderated by the pre-frontal cortex.

7. The Role of the Amygdala
Kluver-Bucy syndrome – taming effect found in rhesus monkeys by removing part of the temporal lobes and therefore destroying the amygdala.
Narabyashi et al (1972) – 43 / 51 patients whose amygdala was destroyed through psychosurgery showed reduced aggression afterwards.

8. Mark & Ervin (1970) – case study of female patient behaviour following electrical stimulation of amygdala.
She exhibited facial grimacing, became very angry and flung herself at the wall.
Ashford (1980) – temporal lobe epileptics often become aggressive, attacking furniture and people.

9. The Role of Neurotransmitters
The neurotransmitter serotonin influences aggressive behaviour.
In research with vervet monkeys, reducing serotonin levels resulted in increased aggressive behaviour, whereas increasing serotonin decreased the aggressive occurrences.
Drugs to raise serotonin levels, such as trytophan have been given to juvenile delinquents and unpredictable institutionalised patients.
The relationships found here are CORRELATIONAL. What are the weaknesses of correlational research?
So… the higher the serotonin level, the lower the aggression.

10. Wong et al (1997) – criminals with violent tendencies have reduced size amygdala
Van Elst et al (2000) aggressive patients with temporal lobe epilepsy, amygdala had lost 20% of its volume.
BUT
Muller et al (2003) showed 6 male psychopaths and 6 male controls a series of positive and negative pictures whilst in MR scanner. Found increased activity in the amygdala.
The exact role of the amygdala in aggression is unclear, but it is certainly a significant one.
Research suggests an interaction between the amygdala and the pre-frontal cortex.

11. The Role of the Prefrontal Cortex
Regulates the emotional responses driven by the amygdala.
Damage to prefrontal cortex results in impulsivity, immaturity and loss of control.
Anderson et al (1999) – damage during infancy related to aggressive behaviour as adults.
Case studies comparing early onset damage with adult onset damage to frontal lobes.
Early onset patients also performed poorly on tests of moral and pro-social reasoning.
This brings in a cognitive element also then. Remember to think ‘approaches’ at all times!

12. Raine et al (1997) – investigated brain activity of 41 murderers using PET scans.
Found reduced glucose metabolism in prefrontal cortex, suggesting this brain area is less active than in normal controls.
Volkow et al (1995) found violent psychiatric patients had reduced cerebral blood flow to prefrontal cortex.
During the 1940s, frontal lobe lobotomies were performed with startling regularity ; partly because of the ‘calming’ effect on patients with a range of mental health problems – from depression to ADHD to OCD.

13. BRAIN STRUCTURE The amygdala is a seat of basic emotions
Stimulation with electrical impulses provokes rage
Lesioning provokes passivity
The prefrontal cortex is the seat of higher thinking and is linked to the amygdala
Damage causes impulsivity, immaturity – linked to aggression

14. Neural explanations of aggression

15. Essentially the argument is
• Low levels of serotonin
• High levels of dopamine
• High levels of testosterone
• Low levels of cortisol
..... are associated with aggression

16. Serotonin AO1
• Thought to inhibit aggressive responses to emotional stimuli
• Low levels associated with increased susceptibility to impulsive behaviour, aggression & violent suicide
• Drugs which reduced serotonin increased measures of hostility and aggression in males (but not females)

17. Dopamine AO1
• Link less well established than serotonin • Giving amphetamines (which increase dopamine) increases aggressive behaviour • Giving anti-psychotics (which reduce dopamine) reduced aggressive behaviour in violent delinquents

18. Testosterone AO1
• Thought to act on areas of brain which control aggression from young adulthood onwards • Thought to be primary biochemical influence on aggression • Salivary testosterone levels were able to differentiate between violent and non-violent criminals and their crimes • Aggressive behaviour in drunken males also positively correlated with testosterone levels • Castrated male mice showed decreased aggression which then increased when given testosterone

19. Cortisol AO1
• Cortisol mediates other hormones such as testosterone • High levels of cortisol inhibit testosterone and so inhibit aggression • So low levels of cortisol associated with increased aggression and studies have supported this. • Low levels of cortisol have been found in habitual violent offenders and also in violent schoolchildren

20. AO2 Serotonin
• Findings on serotonin replicated in vervet monkeys (Raleigh et al (1991)) But issue of: – extrapolation • Meta-analysis (Scerbo 1993) supports low level of serotonin consistently found in aggressive children and adults but found no dopamine abnormalities • Bond – drugs (anti-depressants) that increase serotonin levels to reduce impulsive aggressive behaviour.

21. AO2 Serotonin
• Findings on serotonin also confirmed via studies on anti-depressants • However Lenard (2008) cautions that serotonin not just linked to aggression: also to impulsive behaviour, depression, over-eating, alcohol abuse; violent suicide

22. AO2 Dopamine
• Causal role of dopamine unclear • Perhaps high levels of dopamine are an effect rather than a cause because dopamine is released by performing aggressive acts, so aggression could be being rewarded in the brain.

23. AO2 Testosterone
• Evidence conflicting on role of testosterone • Studies showing positive correlation small samples and self-report measures • Studies mainly correlational (eg. Wagner) so not possible to conclude that testosterone causes aggression • Also testosterone not always associated with negative characteristics: improved sporting and spatial abilities also been found

24. AO2 issues and debates
• Gender bias evident as most research done on males (animals and humans) whereas it is known that there are differences between the genders. • Also cultural bias as most research conducted in western countries

25. AO2 debates
• Reductionist to just consider role of biochemistry alone • Also need to consider genetic factors and brain structure • Eg. Phineas Gage suffered brain injury and showed heightened levels of aggression • Also need to consider the contribution of environmental factors such as situational cues, temperature, noise, overcrowding, and the role of learning

26. AO2 application
• Clearly a very important & useful area of biopsychological research and theory as aggression associated with many anti-social phenomena in society, eg. numerous forms of crime, violence
• If the role of biochemistry can be understood it can perhaps be treated or managed
• Although there would be ethical issues associated with giving people drugs simply to alleviate aggression (ie. for social control) , or male castration, even if it may be in the interests of multiple parties
• Could perhaps be treated more ethically through diet (tryptophan) and exercise

27. Video recap

28. Biological explanations of aggression
Neural and hormonal mechanisms in aggression
Genetic factors in aggressive behaviour

29. Genetic Factors in Aggressive Behaviour
Research methods Twin Studies
Monozygotic twins share all of their genes where as dizygotic twins share only about 50%.
Monozygotic twins have a higher correlation than dizygotic twins. This shows that Genetics are a factor in aggression.
Adoption studies of twins also show a positive correlation between biological parents who are aggressive and the children being aggressive.

30. Genetics and Aggression Studies
Genetics and Aggression Studies often find that aggressive children have aggressive parents Miles & Carey (1997). Carried out meta-analysis of 24 twin and adoption studies Results suggested a strong genetic influence that could account for as much as 50% of the variance in aggression.

31. XYY
Genetics and Aggression Studies often find that aggressive children have aggressive parents.
Other research focussed on the genes themselves and tried to identify important characteristics of genes that might cause these aggressive tendencies – much of this research has focused on chromosomes Sandberg (1961) first identified the 47 XYY karotype. Whilst most normal individuals have 46 chromosomes (23 from each parent), it’s possible for a male to have an extra Y sex chromosome, making the XYY

32. Genetics and Aggression Studies
We often find that aggressive children have aggressive parents The research of Court-Brown ( ) found that those with XYY would be ‘best hospitalised due to an increased likelihood of aggressive behaviour’ This was requested based upon common knowledge of traits associated with each of the sexes. Many textbooks and media depictions of the time adopted this view contributing the widely held belief that XYY males are more aggressive.

33. Warrior Gene (thanks to Ginny for stopping me taking a short cut and making a mistake.)
The so-called warrior gene comprises particular variations in the X chromosome gene that produces monoamine oxidase A (MAOA), an enzyme that affects the neurotransmitters dopamine, norepinephrine, and serotonin. MAOA was the first candidate gene to be linked to antisocial behaviour, identified in 1993 in a large Dutch family that was notorious for violence. (Brunner) – (Does the human “warrior gene” make violent criminals–And what should society do?) Look at the comments for interest. However, the MAOA-L variant is extremely common and occurs in about 40% of the population. (The psycho gene) May have a trigger such as alcohol amphetamines so it has been proposed that offenders on release are banned from alcohol. However, there may be other factors such as high testosterone.

34. Genetic theory Evaluation
In addition to this: A replication of Bandura’s research using twins found no difference in correlations between MZ and DZ twins - Suggesting that aggression may be more a product of the environment.

35. Genetic theory Evaluation Alternative Approach
Nature Vs. Nurture Aronson (1999) reported on non-violent societies. Focussing so heavily on genetics ignores behavioural approach and the role of the environment. Fails to account learning e.g. Bandura’s Bobo doll study Also if aggression was purely biological there would be no cultural differences.

36. Genetic theory Evaluation
Nature Vs. Nurture McGue et al (1992) correlation of MZ and DZ twins
+0.43 for MZ, for DZ
Suggesting that genes play some part in aggressive tendencies as MZ twins share more DNA than DZ twins
suggesting genes play a part

37. Genetic theory Evaluation A02/3
However it may show a greater correlation because MZ twins are likely to be treated in a more similar fashion. Therefore aggression may be more a product of the same the environment rather than genes. Ie: They share nature and nurture

38. Genetic theory Evaluation
Theilgaard (1984) researched the traits of XYY men compared to XY men (including comparing aggression levels). It was found that no single characteristic (except height) was associated with the XYY condition Suggests that the initial view of XYY genotypes influencing aggression may have been over emphasised.
Lagerspetz (1979) bred 25 generations of mice – in each generation the more mice aggressive were made to breed, similarly with the least mice. This resulted in 2 very different strains of mice. One group were super-aggressive overemphasised and the other more docile

39. Fun
Hello

40. Question
Discuss the role of neural and/or hormonal mechanisms in aggression.
(9 marks + 16 marks)

41. Answer
There is a long tradition of research into the neural (brain) and hormonal mechanisms underlying aggressive behaviour. Much of the early work was carried out on non-human animals, but over the last twenty years new technologies have allowed this to be extended into work with humans. Either approach is acceptable. Classic models such as the Papez-Maclean limbic theory involving structures such as the amygdala, septum, and hippocampus have been extended in order to account for conditions such as psychopathy and reactive aggression in humans; areas such as the amygdala, cingulate and prefrontal cortex have been implicated. On the hormonal side most research has focused on the role of testosterone in human and animal aggression. Examiners should be sensitive to depth/breadth trade-offs in answers covering both neural and hormonal mechanisms. Candidates may introduce material on genetic factors in aggression. Such material cannot earn marks unless the implications for neural/hormonal mechanisms are explicit e.g. the association between genetic factors and levels of neurotransmitters such as serotonin and noradrenaline.

42. AO2
The key area for AO2/AO3 marks should be research evidence from studies with humans and non-human animals, and the implications of findings. Methodological evaluation of studies may only earn marks beyond rudimentary if the implications for the role of neural and/or hormonal mechanisms are explicit. Relevant commentary could include the problems of defining aggression, the range of aggressive behaviours, and problems of extrapolating from animals to humans. Gender and cultural issues could also be made relevant to this question. Alternative approaches that focus on the role of aggression such as psychological, social, and cultural aspects, may earn AO2/AO3 marks if used as part of sustained and effective commentary on the role of neural and/or hormonal mechanisms. Indicative issues/debates/approaches in the context of neural and/or hormonal mechanisms in aggression: biological approach; reductionism; free will/determinism; gender and cultural issues; use of non-human animals in research; ethical issues; nature/nurture. Such material must be used effectively to earn AO2/AO3 credit.