Psychology: Aggression

• Neural Mechanism in Aggression

  - limbic system

  - orbitofrontal cortex (OFC) & serotonin
• Hormonal Mechanisms in Aggression

  - testosterone

  - progesterone
• Components of Limbic System

  - amygdala

  - hippocampus

  - hypothalamus

  - thalamus

  - cingulate gyrus

  - fornix
• Role of the Amygdala in Aggression


  - plays an important role in the production of emotions

  
  

  - responsiveness of the amygdala is correlated in aggression (the more responsive the amygdala is the higher the aggression)
• Gospic et al (2011)


  - lab experiment

  
  

  - set-up included 2 players: a proposer and responder

  
  

  - proposer would offer to split money with the responder in a certain way, if the responder agreed the money would be split accordingly

  
  

  - if the responder rejected the offer, both would get nothing

  
  

  - fMRI scans showed that when participants reacted aggressively (rejected an offer) there was a heightened response in the amygdala

  
  

  - also found when benzodiazepine was given it had 2 effects:

  . halved the number of rejections

  . reduced the amount of activity in the amygdala
• Role of Serotonin in Aggression

  - normal levels in the orbitofrontal cortex are associated with the reduced firing of neurons leading to greater self-control

  
  

  - lower levels increases impulsive behaviour including aggression
• Virukkunen et al (1994)


  - compared levels of serotonin breakdown product in the cerebrospinal fluid of violent impulsive offenders and violent non-impulsive offender

  
  

  - levels were significantly lower in impulsive offenders (they also found they had sleep irregularities which serotonin regulates)
• Role of Testosterone in Aggression


  - male hormone associated with aggression

  
  

  - higher levels of testosterone are associated with aggression
• Giammanco et al (2005)


  - castration studies in animals showed that aggression in animals reduced after removing the testes (the source of testosterone)

  
  

  - re-injecting testosterone in the same animals made the aggressive behaviour return
• Daly & Wilson (1988)


  - same-sex violence in men is at its highest at the time in development (after 20yrs) when testosterone is also at its highest
• Role of Cortisol in Aggression

  - stress hormone can negate the effect of testosterone on the body

  
  

  - low levels are associated with an increase in aggression
• Role of Progesterone in Aggression

  - plays a role in aggression in women

  
  

  - progesterone levels vary during the ovulation cycle and are lowest before and after menstrual cycle

  
  

  - low levels of progesterone are associated with higher levels of aggression in women
• Ziomkiewicz et al (2012)

  - found a negative correlation between progesterone levels and self-reported aggression
• Drugs & Serotonin: Strength (AO3)

  - Berman et al (2009) participants took part in a lab-based game that involved giving and receiving shocks

  
  

  - participants were either given a placebo or a dose of paroxetine

  
  

  - participants who took paroxetine (increases serotonin) consistently gave fewer and less intense shocks than the placebo group

  
  

  - proves there is a causal link between serotonin and aggression
• Brain Structures: Limitation (AO3)


  - non-limbic brain structures (OFC) are also involved in aggression

  
  

  - Coccaro et al (2007) OFC activity is reduced in psychiatric disorders featuring aggression - the OFC's impulse control function is disrupted increasing aggression

  
  

  - suggests neural regulation is more complex that theories focusing on the amygdala suggest
• Animal Research: Strength (AO3)

  - animal research supports hormonal explanations of aggression

  
  

  - Giammanco et al's review confirms the role of testosterone in aggression:

  . increase in testosterone and aggression in male rhesus macaque monkeys during mating season

  . castration of male rats reducing testosterone and mouse-killing, injecting female rats with testosterone increased both

  
  

  - demonstrates the role testosterone plays in aggression in a range of animal species

  
  

  - evaluation extra: hormonal mechanism are similar in mammals and humans however human aggression is more complex than animal aggression
• Dual-Hormone Hypothesis: Limitation (AO3)


  - Carré & Mehta (2011) hypothesise that high levels of testosterone only cause aggression when cortisol levels are also low

  
  

  - high levels block the effect of testosterone

  
  

  - therefore the combine activity of testosterone and cortisol may be a more comprehensive explanation
• Twin Studies


  - suggest that heritability ( genetic factors) accounts for 50% of the variance in aggression

  
  

  - monozygotic twins (MZ) share 100% of their genes but dizygotic twins (DZ) only share 50%

  
  

  - concordance between MZ twins indicates that the behaviour observed is more likely to have a genetic basis
• Cocarro et al: Twin Studies (1997)


  - studies men who were either DZ twins or MZ twins

  
  

  - for aggressive behaviour defined as physical assault researchers found concordance rates for 50% of MZ twins and 19% for DZs

  
  

  - for verbal aggression the figures were 28% (MZ) and 7% (DZ)
• Adoption Studies


  - similarities between an adopted child and their biological parents suggest that genetic influences are at play

  
  

  - similarities between an adopted child and their adoptive parent suggest environmental factors are at play
• Rhee & Waldman: Adoption Studies (2002)


  - carried out a meta-analysis of adoption studies of direct aggression and anti-social behaviour (which often features aggressive behaviour)

  
  

  - found genetic influences account for 41% of variance in aggression - similar to findings from twin studies
• MAOA Gene


  - MAOA control the production of the enzyme monoamine oxidase A (MAO-A) which regulates serotonin

  
  

  - key point:

  . MAOA = gene

  . MAO-A = enzyme

  
  

  - the low activity variant MAOA-L results in lower activity of the MAO-A enzyme which has been linked to increased levels of aggression
• Lea and Chambers (2007)

  - MAOA was nicknamed the 'warrior gene' due to research

  
  

  - found the MAOA-L variant was possessed by 56% of New Zealand Maori men (compared with 34% of Caucasians)

  
  

  - Maori people have had a reputation for being ferocious warriors hence the nickname
• Brunner et al (1993)


  - studies 28 men for a Dutch family who were repeated involved with violent impulsive criminal behaviour including rape, attempted murder and physical assault

  
  

  - found the men had abnormally low levels of the MAO-A gene and the MAOA-L gene variant (sometimes known as Brunner's Syndrome)
• Gene-Environment (GxE) Interactions


  - although genes play a role in aggression they don't function in isolation

  
  

  - MAOA-L gene only tends to result in adult aggressive behaviour when combined with early traumatic life experiences
• Frazetto et al


  - found an association between higher levels of anti-social aggression and the MAOA-L gene variant in men

  
  

  - however this was only the case with those with significant childhood trauma (physical or sexual abuse) before the age of 15yrs

  
  

  - those who hadn't experienced extreme childhood trauma despite having the MAOA-L gene didn't have particularly high levels of aggression

  
  

  - strongly suggesting evidence for a gene-environment interaction (aka diathesis stress)
• Research Support: Strength (AO3)

  - Mertins et al (2011) found men with the high variant MAOA gene (MAOA-H) were more cooperative and made fewer aggressive moves that low-activity participants in a money distribution game

  
  

  - supports the relationship between MAOA gene activity and aggression
• Research Support: Counterpoint (AO3)

  - participants with the low activity gene variant became more cooperative when they we told others were being cooperative as well (giving away money)

  
  

  - knowledge of a social norm also played a role in determining how aggressive MAOA-L participants were

  
  

  - suggests genes are influenced by the environment factors that are at least as important
• Complex Link: Limitation (AO3)


  - the precise mechanisms of the MAOA-serotonin and the role it plays in aggression is unclear

  
  

  - the MAOA-L variant gene causes low activity of the MAO-A enzyme which lead to higher serotonin because there is more serotonin left for synaptic transmission

  
  

  - its may be more accurate to say people with the MAOA-L variant have had their serotonin levels disrupted rather that being higher or lower
• Problems with Twin Studies: Limitations (AO3)

  - twins studies have questionable validity

  
  

  - it is assumed that MZ twins are treated as similarly as DZ twins (environments assumption)

  
  

  - however part of environmental factors are how twins are treated

  
  

  - MZ twins are more likely to be treated the same by parents and peers

  
  

  - meaning concordance rates are conflated and genetic influences of aggression may not be as great as twin studies suggest
• Nature & Nurture (AO3)

  - while genetics have been proven to have an effect on aggression, environmental factors have an influence on how genes are expressed e.g. childhood trauma, criticisms of twins studies

  
  

  - it could be argued that environmental factors are more important, while there are dispositional factors in aggression these are only expressed in certain conditions
• Adaptive Functions of Aggression

  - defeated animals are rarely killed but instead spread out over a wider area reducing competition for resources.

  
  

  - victorious animals have the resources and establish dominance in a hierarchy.
• Pettit et al (1988)


  - studied groups of young children and observed how aggression played a role in developing hierarchies
• Ritualistic Aggression


  - Lorenz (1966) found intra-species fights resulted in very little physical damage

  
  

  - most aggressive encounters consisted of ritualistic signalling (displaying teeth and claws, facial expressions of threat)

  
  

  - confrontations would also end with ritual appeasement displays ( e.g. exposure of vulnerable areas)

  
  

  - adaptive as species would die out if every encounter ended in the death of the victor
• Innate Releasing Mechanism (IRM)

  - an in-built physiological mechanism process or structure e.g. a network of neurons in the brain

  
  

  - environmental stimulus triggers the IRM which 'releases' a set of behaviours (Fixed Action PAttern)
• Fixed Action Patterns (FAP)

  - Lea (1984) identified 6 major features of FAPs:

  . Stereotyped: don't tend to deviate

  
  

  . Universal: same behaviour is found in each member of a species

  
  

  . Unaffected by Learning: the same for each individual regardless of learning

  
  

  . Ballistic: once behaviour is triggered it can't be stopped until its complete

  
  

  . Single-Purpose: only occurs in specific situation and no other

  
  

  . Specific Sign Stimulus: a response to a specific stimulus or releaser (in the case of communication between members of the same species)
• Tinbergen (1951)


  - investigated aggressive behaviour in male sticklebacks during mating season

  
  

  - presented male sticklebacks with series of wooden models of varying shape and size with red spots on the underbelly (IRM) and those without

  
  

  - regardless of the shape of the model of stickleback if it had a red spot sticklebacks would act aggressively

  
  

  - found that FAPs were unchanging in each encounter and also ran their course once started
• Research Support: Strength (AO3)

  - multiple strands of research suggests that there is a genetic basis to aggression:

  . Brunner et al (1993)

  
  

  . Wilson & Daly (1996)

  
  

  . Twin & Adoption Studies
• Research Support: Counterpoint (AO3)

  - aggressive behaviours vary from culture to culture

  
  

  - Nisbett (1993) found one type of homicide was common in Southern men in the US (caused by reactive aggression) than men from the North

  
  

  - Nisbett concluded differences were due to the 'culture of honour' in the South which is less prevalent in the North

  
  

  - suggests aggression can also be shaped by social norms rather than innate dispositional factors
• Ritualistic Aggression: Limitation (AO3)


  - not all inter-species aggression is ritualistic in nature

  
  

  - Goodall (2010) observed a '4 year war' in which chimps from one community systematically killed chimps from another (holding down rival chimps while other attacked it)

  
  

  - violence continued despite appeasement rituals

  
  

  - challenges the ethological view has evolved into a self-limiting and relatively harmless ritual