Aggression: Neural and Hormonal

Aggression: Neural and Hormonal

1. Serotonin

   • • Serotonin reduces aggression. » Calming inhibitory effect on neural firing. » Can cause reduction in aggression behaviour. » Inhibits responses to emotional stimuli. • Low levels of serotonin remove inhibitory effect. » Less able to control impulsive behaviours. • Mann et al (1990) – gave 35 ppts dexfenfluramine (depletes serotonin). » Used questionnaire to assess hostility and aggression. » Aggression levels on the questionnaire increased after taking the drug – although only in males.
     • AO2: Supported by Raleigh et al (1991). • Studied vervet monkeys fed diet containing tryptophan (increases serotonin). » Diet high in tryptophan = decreased levels of aggression. » Diet low in tryptophan = exhibited increased aggressive behaviours. •Suggests the difference in aggression can be attributed to levels of serotonin.
       • AO3: • An issue with using vervet monekeys is the Lack of external validity (population validity) as it is animal research trying to explain human behaviours. • Humans have different, more complex cognitions. » Cannot be generalised to aggression in humans.
     • AO2: Supported by Badawy (2006). • Alcohol consumption disturbs metabolism of serotonin. » Heavy alcohol intake depletes serotonin in normal individuals. » Depletion may induce aggressive behaviours in susceptible individuals. • Explains why some people are aggressive after consuming large amounts of alcohol – low levels of serotonin.
       • AO3: • Ethical issues. • Unethical to make people consume large amounts of alcohol to see the effect on aggressive behaviours. • Ppts have no protection from harm – it is unhealthy and may become unpredictable.

2. Dopamine

   • • Dopamine increases aggressive behaviours. • Lavine (1997) – increased dopamine levels as result of taking amphetamines is associated with increased aggressive behaviour. • Dopamine is associated with pleasurable stimuli. » Release of dopamine during aggression reinforces aggressive behaviours. » Seek out encounters for rewarding sensation.
     • AO2: Supported by Ferrari et al. • Allowed rat to fight at same time every day for 10 days. • 11th day rat did not fight but measured dopamine levels in brain. » Increased in anticipation of fight. • Experience changed animal’s brain chemistry by altering levels of dopamine consistent with aggressive behaviour.
       • AO3: • Theory is reductionist. • Only focuses on biological approach suggesting that neurotransmitter levels are the cause of aggression. • Fails to consider social learning theory. » Aggression learnt vicariously through models and repeated due to positive reinforcements e.g. attention from others.

3. Testosterone

   • • Testosterone increases aggression. » Thought to influence aggression from young adulthood onwards. » Acts on brain areas controlling aggression. • Correlational link – testosterone makes it more likely that a behaviour will be expressed. • Dabbs et al found that violent criminals with history of violence had higher testosterone levels than non-violent criminals. » Shows clear correlation between higher testosterone levels and aggression in violent criminals.
     • AO2: Supported by meta-analysis by Archer (1991). • Analysed results of 230 meals over 5 studies. • Low positive correlation between testosterone and aggression. • Shows testosterone does have an influence on aggression. » However, type of ppt and measurement of aggression differed substantially between studies.
       • AO3: • Gender bias. • Lacks population validity as only involves male ppts and cannot be generalised to include effects of testosterone on aggression in females. • Research suggests association between testosterone and aggression is higher for females than males. » Further study – women with higher testosterone levels had higher occupational status – possibly a result of being more assertive.

4. Cortisol

   • • Cortisol reduces aggression. • Mediating effect on testosterone. » Possibly because increases anxiety and likelihood of social withdrawal (Dabbs et al 1991). • Inverse correlation – lower levels of cortisol associated with higher levels aggression. • Higher cortisol levels inhibit testosterone and so reduce aggression.
     • AO2: Supported by McBurnett et all (2000). • Longitudinal study over 4 years – 38 boys ages 7-12 with behavioural problems. • Consistently low cortisol levels. » Began antisocial acts at younger age. » 3 times more aggressive symptoms compared to higher/fluctuating cortisol levels. • Cortisol levels ‘strongly and inversely related to aggressive conduct disorder.
       • AO3: • Theory is deterministic. • Only focuses on biological mechanisms and suggests that neurotransmitters and hormones are the sole cause of aggression. • Fails to consider free will of those who choose to be aggressive despite having high serotonin /cortisol or low dopamine/testosterone. » Would, according to the theory, have the opposite effects.