Aggression Flashcards
Papez and Maclean linked which system to emotions?
Limbic system
What 3 parts of the brain are included in the limbic system?
- Amygdala
- Parts of the hippocampus
- Hypothalamus
How has the amygdala been implicated in aggression?
- Aggressive reactions were associated with a fast and heightened response by the amygdala
- Benzodiazepine (reduces arousal of the autonomic nervous system) decreased amygdala activity and decreased aggression
How has low serotonin been implicated in aggression?
Decreased serotonin disturbs this mechanism, reduces self-control and increases impulsive behaviours, including aggression (Denson et al.)
What do normal levels of serotonin in the orbitofrontal cortex do to neuronal activity?
Normal levels of serotonin in the orbitofrontal cortex inhibit neurons (reduced firing) and are linked to greater behavioural self-control (dampens neuronal activity)
What did Virkkunen find regarding levels of the serotonin metabolite 5-HIAA in violent offenders in comparison with non violent offenders?
Virkkunen et al. found lower levels of serotonin metabolite 5-HIAA in violent, impulsive offenders compared with non-impulsive offenders (compared levels of 5-HIAA in cerebrospinal fluid between impulsive and non-impulsive offenders)
How has testosterone been implicated in aggression?
- Testosterone helps regulate social behaviour via influence on brain areas involved in aggression
- Males are more aggressive towards other males at 20+ years, when testosterone levels peak (Daly and Wilson)
Dolan et al. found a positive correlation between what and what in male offenders with histories of impulsively violent behaviour and personality disorders?
Dolan et al. found a positive correlation between plasma testosterone and aggression in male offenders with histories of impulsively violent behaviour and personality disorders
According to Giammanco et al., what reduces aggression in many species, and what restores it?
Removing testes (castration) reduces aggression in many species, injecting testosterone restores aggressive behaviour (Giammanco et al.)
During the menstrual cycle, when are progesterone levels lowest?
During and just after menstruation
According to Ziomkiewicz et al., there is a negative correlation between progesterone levels and self-reported aggression. What does this mean?
Low progesterone = high aggression
Non-limbic systems are also involved in aggression. How is this a weakness of the neural mechanisms in aggression?
- Limbic structures function jointly with the non-limbic orbitofrontal cortex (OFC). This is involved in impulse regulation and inhibition of aggression
- Coccaro et al. claim OFC activity is reduced in psychiatric disorders featuring aggression - this disrupts the OFC’s impulse control function, which increases aggression
- This shows that the neural regulation of aggression is more complex than theories focussing on the amygdala suggest
There has been research into the effects of drugs on serotonin (Berman et al.). How is this a strength of neural mechanisms in aggression?
- Berman et al.’s participants took part in a lab-based game, giving and receiving electric shocks in response to provocation
- Participants who took paroxetine (enhances serotonin) consistently gave fewer and less intense shocks than a placebo group
- This study is evidence of a causal link between serotonin and aggression
Discuss whether neural factors are directly or indirectly linked to aggression as an evaluation point of neural mechanisms in aggression
- Neural factors may be directly linked to aggression, e.g. Gospic et al. Serotonin also reduces aggression by inhibiting neuronal activity
- HOWEVER, neural factors may be indirect. Denson et al. found a link between serotonin and aggression but other factors may influence this link
- This suggests that the evidence that neural mechanisms are related to aggression is reasonably strong, but this relationship is probably not direct
There is research support from Giammanco et al. with non-human animal studies. How is this a strength of hormonal mechanisms in aggression?
- Giammanco et al.’s review confirms the role of testosterone, e.g. increase in testosterone and aggression in male rhesus monkeys during mating season
- In rats, castration of males reduces testosterone and mouse-killing. Injecting female rats with testosterone increases both
- These findings show that testosterone plays a key role in aggression in a range of animal species
The evidence linking testosterone and aggression is mixed. How is this a weakness of hormonal mechanisms in aggression?
- Carré and Mehta’s dual-hormone hypothesis suggests high levels of testosterone lead to aggression, but only when cortisol levels are low
- High cortisol blocks testosterone’s influence on aggression. Cortisol is a hormone that is key to the body’s chronic stress response
- Therefore, the combined activity of cortisol and testosterone may be a better predictor of aggression than either hormone alone
Discuss animal research as an evaluation point for hormonal mechanisms in aggression
- Hormonal mechanisms in human and mammalian aggression are likely to be similar. Research on this shows that most knowledge about hormones comes from non-human studies
- HOWEVER, aggression in humans is more complex than in other mammals. Carré and Mehta’s findings about cortisol apply only to humans and cognitive factors are involved
- Therefore, animals studies can help us understand hormonal influences on aggression but findings must be treated cautiously because human aggression is more complex
What were the concordance rates for DZ and MZ adult male twins found by Coccaro et al. for physical aggression?
For direct physical aggression, they found concordance rates of 50% for MZ twins and 19% for DZ twins
What were the concordance rates for DZ and MZ adult male twins found by Coccaro et al. for verbal aggression?
For verbal aggression, the figures were 28% for MZ twins and 7% for DZ twins
What do similarities in aggressive behaviour between an adopted child and biological parents suggest?
Genetic influences are operating
What do similarities in aggressive behaviour between an adopted child and adoptive parents suggest?
Environmental influences are operating
What percentage variance of aggressive behaviour is genetic, according to a meta analysis of 51 adoption studies by Rhee and Waldman?
41%
According to Rhee and Waldman, does gender affect variance in aggression?
No
Low levels of which neurotransmitter is the MAOA (warrior) gene linked to?
Serotonin
What does the candidate gene MAOA do in terms of regulating serotonin?
- Controls production of the enzyme MAO-A which regulates serotonin
- Serotonin is thought to play a role in impulsive aggression
Genes come in different variants. Low levels of MAOA (MAOA-L) is linked to what?
Increased aggression
According to Lea and Chambers, why has the MAOA-L variant been nicknamed the warrior gene?
- MAOA-L variant possessed by 56% of New Zealand Maori males (34% Caucasians)
- Maori warriors historically ferocious
Outline the Brunner syndrome study, involving the Dutch family
- Brunner et al. studied 28 male family members (Dutch family) repeatedly involved in impulsively violent criminal behaviours (e.g. rape, attempted murder, assault)
- These men had both abnormally low levels of the enzyme MAO-A in the brains and the MAOA-L variant (the “Brunner syndrome”)
Outline the Caspi GxE (gene-environment interactionism) study
- life histories of 442 boys, New Zealand
- 154 maltreated in first 10 years: sexual abuse, beatings or rejection by mother or foster parents
- 55 had a low activity variant: 12% of the sample, but were responsible for 44% of all crimes committed
- “It is very common in the population. One third of us have it, so the gene apparently doesn’t do much of anything, it doesn’t cause a handicap in any way, unless we are also maltreated”
There is support for role of the MAOA gene. How is this a strength of the genetic explanation for aggression?
- Research shows the low activity variant is associated with high aggression. Mertins et al. found the converse is also true
- Male participants with the high activity MAOA gene variant were more cooperative and less aggressive in a money-distributing game
- This finding supports the relationship between MAOA gene activity and aggression, increasing the validity of this genetic theory of aggression
Mertins et al. found the genetic influence on aggression diminished in certain situations. How is this a weakness of the genetic explanation for aggression?
- Even participants with the low activity MAOA variant behaved cooperatively when they knew others were also being cooperative - the genetic effect diminished
- Therefore, genes do not operate in a vacuum but are influenced by environmental factors that are at least as important in aggression
The mechanism linking the MAOA gene and serotonin is unclear. How is this a weakness of the genetic explanation for aggression?
- Research shows aggression is linked with low serotonin, but we expect people with MAOA-L to have high serotonin
- This is because low-activity enzyme means serotonin is not deactivated (the normal outcome), so should leave more serotonin - better viewed as disrupted activity (not high or low)
- This shows that the relationship between the MAOA gene, serotonin and aggression is not yet understood, but has been exaggerated by the media (warrior gene = pop psychology)
The genetic explanation for aggression has real world applications. How is this a strength?
- A new study of 900 offenders from Finland supports the link between MAOA and violent crime
- For instance, Tiihonen et al. found a low-activity version of the MAOA gene was associated with violent crime and individuals with this deficiency were 13 times more likely to have a history of repeated violent behaviour and at least 5-10% of all violent crime in Finland could be attributed to individuals with these genotypes
- HOWEVER, they also acknowledge that they haven’t found any single gene that codes for violence and the environment is equally important, as found by Caspi et al
Twin studies may lack validity. How is this a weakness of the genetic explanation for aggression?
- Both individuals in a twin pair share the same environment (raised together). But DZ twins may not share environments to the same extent that MZs share theirs
- The equal environments assumption is wrong because MZs are treated very similarly (e.g. parents praise them equally for aggression), but DZs are treated less similarly
- This means that concordance rates are inflated and genetic influences on aggression may not be as great as twin studies suggest
Evaluate the free will vs determinism debate as part of the genetic explanation for aggression
- Despite biological psychologists playing down the view that human aggression is genetically determined, there have been several instances of defence lawyers using genetic information to reduce sentences
- HOWEVER, the ‘genes for violence’ view is exaggerated, as highlighted by studies such as Caspi
- In combination with many other factors these genes may make it harder for individuals to control violent urges, but they do not predetermine people for a life of crime and free will advocates that the mental capacity of the individual to understand the consequences of what he or she is doing is most important
