Neural and Hormonal Mechanisms in Aggression

A01 Biological explanations suggest that aggressive behaviour can be in the makeup of an individual rather than in the environment around them. 

• Low levels of SEROTONIN are associated with aggressive behaiour. 
• Serotonin usually reduces aggression by inhibiting responses to stimuli that might otherwise lead to aggressive behaviour.
• Low levels of serotonin have been associated with an increased susceptibility to impulsive and aggressive behaviour. 
• MANN ET AL: gave 35 healthy people dexfenfluramine ( reduced levels of serotonin). Using a questionnaire he found that the drug caused MEN to become violent and aggressive. 

DOPAMINE -Increases in dopamine levels have been shown to produce increases in aggressive behaviour. - Demonstrated in a study by LEVINE, used amphetamines ( to increase dopamine activity in the brain) and found an associated increase in levels of aggresive behaviour. 

BUITELAAR: showed that in a study, that reduced dopamine levels through the use ofanitpsychotic drugs have reported a reduction in aggressive behaviour. 

Serotonin -SCERBO AND RAINE: Support for the importance of serotonin: A meta-anaylsis of studies found that lower levels of serotonin in individuals were described as being aggressive. This supports the claims that serotonin depletion leads to implusive behaviour which leads into aggressive beahviour in various forms. 

• EVIDENCE FROM STUDIES OF NON HUMAN ANIMALS: Evidence for the importance of serotonin comes from studies of animals that have been specially bred for domestication and for increasingly docile temperaments. These animals have shown a corresponding increase, over generations, of levels of serotonin in the brain. As high levels of serotonin block the stimuli that may lead to aggressive behaviour. 

Dopamine- Evidence is inconclusive: A study by COUPPIS AND KENNEDY suggests that it may be a consequence rather than a cause. Some individuals may seek out aggressive encounters because dopamine is increased as a POSTIVE REINFORCER in the brain when they enage in aggressive behaviours. - THERE IS RESEARCH THAT CHALLENGES THIS: SCERBO & RAINE: A meta anaylsis examined neurotransmitter levels in antisocial children and adults. They found lower levels of serotonin in individuals described as aggressive, but found no rise or fall of dopamine levels in this gourp compared to normal individuals.

A01  Testosterone is a male sex hormone and is thought to influence aggression from young adulthood onwards due to its action on the brain areas involded in controlling aggression 

• TESTOSTERONE is thought to increase aggression
• THE CHALLENGE HYPOTHESIS: Wingfield et al: Monogamous species levels should only raise above the baseline breeding level in response to social challenges such as male-male aggression or threat to status.
• DABBS ET AL: Salivary testosterone in violent and non-violent criminals: Those with thehighest testosterone levels had history of primarliy violent crime, those with lowesttestosterone had non-violent crimes.

CORTISOL - High levels of cortisol inhibit testosterone levels and so inhibit aggressinon

• Low levels of cortisol have been reported in habitual violent offenders - VIRKKUNEN - and in violent schoolchildren - TENNES AND KREYE
• This suggests that, although testosterone may be the main biochemical influence on aggressive behaviour, low cortisol levels increase the likelihood of aggresive behaviour. 

A02 - Testosterone- MAZUR: Claims that aggressive behaviour is just one form of dominance behaviour. In humans, the influence of testosterone on dominance is likely to be expressed in more vaired and subtle ways rather than only through aggressive behaviour. 

• EVIDENCE IS INCONSISTANT: As although many studies show a link between testosterone and aggression, many others do not. Most of the studies that do find a positive correlation have a small SAMPLE of men within prisons relying on slef-reports of aggressive behaviour which are - unrealiable, demand characteristics etc. 

A02 - Cortisol 

• SUPPORT: MCBURNETT ET AL studied boys with aggressive conductive disorder: Boys with consistantly low cortisol levels had three times the level of aggressive sympotoms, compared to boys who had fluctuating levels of cortisol. This demonstrates that cortisol levels are strongly and inversly related to levels of aggression
• One possible reason that this relationship exits is that boys who have low cortisol levels might be less afraid of punishment. As a result, such children may not experience anxiety at the threat of punishment and so do not avoid aggressive conditions. 

S: The theory can be said to be reductionist. Biological explanation alone is insufficient to explain aggression in humans.

E: As human social behaviour is so complex and influenced by a variety of factors both internal and external. Also links between serotonin, aggression and testosterone are more explicit in animals but humans are more complex and react with different stimuli from external environment that affect aggressive behaviour.

E: Therefore it can be said the theory is invalid as it lacks the evidence that would suggest that all humans react in the same way without any external or internal factors that would contribute to aggression. And thus the theory cannot be generalised to all populations. 

S: Most studies of the links between testosterone and aggression have involved male ppts, and there is a lack of research on women therefore this theory can be said to be gender bias.

E: Yet research suggests that the link between testosterone and aggression may be even stronger for females according to ARCHER ET AL - suggest that succesful career women have higher testosterone levels

E: Therefore this theroy does not take into account the effect of levels of testosterone on female aggression. And so it is difficult to generalise this theory to both men and women.