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Summary - Aggression
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Complete notes for AQA Paper 3 topic of Aggression. Notes from Illuminate Publishing textbook Year 2.
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Chapter 11: AggressionAGGRESSION
Neural and Hormonal Mechanisms in Aggression
Limbic System – subcortical structures in brain closely involved in regulating emotional behaviour
Serotonin – neurotransmitter with widespread inhibitory effects throughout brain
Testosterone – hormone from androgen group mainly in male testes
NEURAL MECHANISMS IN AGGRESSION
The Limbic System
Papez (linked) and Maclean (revised): linked limbic system to emotional behaviours
Defined system as the hypothalamus, amygdala and parts of hippocampus
Reactivity of amygdala in humans is important predictor of aggressive behaviour – e.g. heightened
activity = heightened aggression
Katharine Gospic: The Ultimatum Game – researchers found when participants rejected an unfair
monetary reward (social provocation)
o fMRI scans showed fast and heightened response in amygdala when provoked
o Spikes less drastic when benzodiazepines used
o Suggests strong link between action of ANS and aggression
Orbitofrontal Cortex and Serotonin
Serotonin has widespread inhibitory effects on brain
Normal levels of serotonin in OFC linked with reduced firing of neurons, associated with greater
behavioural self- control
Decreased serotonin (deficiency) reduces self- control, leads to increased impulsive behaviour
Virkkunen: compared levels of serotonin breakdown product (5-HIAA) in cerebrospinal fluid of violent
impulsive/ non- impulsive offenders – levels lower in impulsive offenders
EVALUATION
Other Brain Structures
More recent research showing non- lambic brain structures involved in aggression
Limbic structures function together with OFC
OFC involved in regulation and inhibition of aggressive behaviour
Emil Coccaro: OFC activity reduced in those psychiatric disorders that feature aggression
Reduced activity disrputs OFC’s impulse- control function
Neural regulation of aggression more complex than theories focusing on amygdala suggest
Drugs and Serotonin
Drugs that increase serotonin found to reduce levels of aggressive behaviour
Berman: gave participants either a placebo or dose of paroxetine, then took part in lab- based game
involving either giving or receiving electric shocks in response to provocation
Paroxetine group consistently gave fewer and less intense shocks than placebo
Evidence of casual link between serotonin function and aggression
HORMONAL MECHANISMS IN AGGRESSION
Testosterone
Male sex hormone responsible for development of masculine features – linked to aggressive behaviour
Many observed men more aggressive than women – men become more aggressive towards other men
at a time in development when testosterone levels are highest
Role in regulating social behaviour via its influence on aggressive behaviour (Giammanco)
Castration studies show removing the testes reduces aggression in the males of many species
Evidence for similar association in humans come from prison studies – Dolan: positive correlation
between testosterone levels and aggressive behaviours in sample of 60 offenders, had personality
disorders such as psychopathy
Progesterone
Plays important role in aggression in women
Levels vary during ovulation cycle and lowest just after menstruation
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, Chapter 11: Aggression
After ovulation cycle progesterone at its lowest
Ziomkiewicz: negative correlation between progesterone levels and self- reported aggression
o Suggestion that low levels of progesterone linked to increased aggression in women
EVALUATION
Animal Research
Giammanco’s reviews of studies confirms role of testosterone
E.g. male rhesus macaque monkeys there is increase in testosterone and aggressive behaviour during
mating season
In rats, castration of males reduces testosterone and mouse- killing behaviour
Injecting female rats with testosterone increases mouse- killing
Therefore findings show role of testosterone in a range of species
Dual- Hormone Hypothesis
Mixed evidence of link between testosterone and aggression in humans
Carré and Mehta: developed dual- hormone hypothesis: claimed high levels of testosterone leads to
aggressive behaviour but only when cortisol levels are low – when cortisol is high, testosterones
influence on aggression is blocked
Cortisol (hormone) plays central role in body’s response to chronic stress
Combined activity of testosterone and cortisol may be better predictor of aggression than either
hormone
Genetic Factors in Aggression
Genetic Factors – genes consist of DNA strands. DNA produces ‘instructions’ for general physical features
of an organism (e.g. eye colour, height) and specific physical features (e.g. neurotransmitter levels and sizes
of brain structures) – may impact psychological features (e.g. intelligence and mental disorders) and are
transmitted from parents to offspring
MAOA Gene – responsible for activity of enzyme monoamine oxidase in the brain, low- activity variant
closely associated with aggressive behaviour
GENETIC FACTORS IN AGGRESSION
Twin Studies
Several suggest heritability (genetic factors) account for 50% of variance in aggressive behaviour
Emil Coccaro: studied men either MZ or DZ twins (MZ share 100%, DZ share 50% genes – expect to
find greater similarities between MZ if influenced by genetics)
o Researchers found concordance rates of 50% for MZ twins and 19% for DZ’s
o Verbal aggression: 28% (MZs), 7% (DZs)
Adoption Studies
Similarities in aggressive behaviour between an adopted child and biological parents suggest genetic
influences operating
Similarities between adopted child and adopted parents show environmental influences operating
Rhee and Waldman: meta- analysis of adoption studies of direct aggression and antisocial behaviour
o genetic influences accountable for 41% of variance in aggression (in line with twin study
findings)
The MAOA Gene
Control production of enzyme called monoamine oxidase A
MAO– A regulates neurotransmitter serotonin
Low activity variant (MAPA- L) results in low activity of the MAO-A enzyme – linked to aggressive
behaviour
Nicknamed ‘warrior gene’ due to research by Lea and Chambers: showed MAOA-L variant possessed
by 56% New Zealand Maori men – vs 34% Caucasians
o Historically had reputation for most ferocious warriors
Link between MAOA-L and aggression cemented by Bruner
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