2. Neural and Hormonal Mechanisms in Aggression BATs A01 -Outline biochemical influences on aggressive behaviour (hormones and neurotransmitters) - Outline how brain structure can affect aggressive behaviour A02/3 Evaluate the effectiveness of biological explanations of the cause of aggression P66-67
3. Essentially the argument is Low levels of serotonin High levels of dopamine High levels of testosterone Low levels of cortisol ..... are associated with aggression 3 Neurotransmitters hormones
4. Serotonin AO1 Thought to inhibit aggressive responses to emotional stimuli Low levels associated with increased susceptibility to impulsive behaviour, aggression & violent suicide Mann et al (1990) – drugs which reduced serotonin increased measures of hostility and aggression in males (but not females) Scerbo & Raine (1993) – meta-analysis supports low level of serotonin but found no dopamine abnormalities 4
5. Dopamine AO1 Link less well established than serotonin Lavine (1997) – giving amphetamines (which increase dopamine) increases aggressive behaviour Buitelaar (2003) – giving anti-psychotics (which reduce dopamine) reduced aggressive behaviour in violent delinquents 5
6. Testosterone AO1 Thought to act on areas of brain which control aggression from young adulthood onwards Thought to be primary biochemical influence on aggression Dabbs et al (1987) – salivary testosterone levels were able to differentiate between violent and non-violent crimes Lindman et al (1987) – aggressive behaviour in drunk males positively correlated with testosterone levels Wagner et al (1979) castrated male mice showed decreased aggression which then increased when given testosterone again Archer (1991) and Book et al (2001) – meta analyses with weak but positive correlation between testosterone and aggression Wingfield et al (1990) – argue that testosterone levels rise in monogamous species in response to social challenges 6
7. 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 Virkuunen (1985) found low levels of cortisol in habitual violent offenders; Tennes & Kreye (1985) same in violent schoolchildren 7
8. AO2 / AO3 Findings on serotonin replicated in vervet monkeys (Raleigh et al (1991)) Tryptophan - increases serotonin levels in brain Monkeys given high amounts of tryptophan – less aggressive, and vice versa But issues of: extrapolation Ethics 8
9. AO2 Findings on serotonin also confirmed via studies on anti-depressants Bond (2005) – anti-depressant drugs that elevate Serotonin – reduce irritability and impulsive aggression However Lenard (2008) cautions that serotonin not just linked to aggression: also to impulsive behaviour, depression, over-eating, alcohol abuse; violent suicide 9
10. AO2 Causal role of dopamine unclear Perhaps high levels of dopamine are an effect rather than a cause? Couppis and Kennedy (2008) – mice - reward pathway in brain activated in response to an aggressive event – dopamine acts as a positive reinforcer. Seek out aggressive encounter because they get a rewarding sensation from it. 10
11. AO2 / AO3 Evidence conflicting on role of testosterone Studies showing positive correlation - small samples, mostly males in prisons 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 11
12. AO2 clarification needed Mazur (1985) - Need to distinguish between aggression & dominance Issue relates to the internal validity if the research as studies may be measuring different things, making comparison of results difficult 12
13. AO2 issues Gender bias evident as most research done on males (animals and humans) whereas it is known that there are differences between the genders in androgens Also cultural bias as most research conducted in western countries Animal research – can’t generalise to humans, ethics 13
14. AO2 debates Physiologically reductionistic 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 14
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16. If the role of biochemistry can be understood it can perhaps be treated or managed
17. 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
18. Could perhaps be treated more ethically through diet (tryptophan) and exercise15
19. Brain Structure and Aggression – A01 The amygdala is a seat of basic emotions Stimulation with electrical impulses provokes rage Lesioning (removing all or part of amygdala) provokes passivity The prefrontal cortex is the seat of higher thinking and is linked to the amygdala Damage causes impulsivity, immaturity – linked to aggression
20. Animal Studies – 1930’s - removal of amygdala in aggressive animals – taming effect LeDoux 1996 – sustained stimulation of amygdala in lab animals resulted in fear and rage Human studies – Narabayashi et al (1972) – 43/51 patients who hd amygdala removed showed reduced aggression, Heimberger (1978) 48/58 patients showed improvement in aggressive behaviour Temporal lobe epilepsy – Ashford (1980) – become aggressive to people close by Parts of amygdala ‘wired’ to produce aggression, whereas prefontal cortex offers control of aggression Brain Structure and Aggression – A02
21. Case Study – Phineas Gage Use the internet to investigate the case of Phineas Gage. Describe what actually happened to him Critically analyse the extent to which Gage’s case provides evidence for the argument that brain structure influences aggressive behaviour. Explain your answer
