Aggression Flashcards
Name neural mechanisms involved with aggression
- the limbic system (amygdala and hippocampus)
- serotonin
Describe the role of the limbic system
- area of the brain that helps to coordinate behaviours that satisfy motivational and emotional urges, such as aggression and fear
- Papez and Maclean linked the limbic system to emotional behaviours including aggression
- 2 key structures associated with aggression are the amygdala and hippocampus
Describe the role of the amygdala in aggression
- responsible for quickly evaluating the emotional importance of sensory information and generating an appropriate response
- If certain areas of the amygdala are stimulated electrically then an animal responds with aggression such as snarling and adopting an aggressive posture
- If the same area is surgically removed, the animal no longer responds to stimuli that would have led to rage
- Similarly, in humans, removal of the amygdala results in a reduction in violent behaviour
Research surrounding the role of the amygdala in aggression
- Narabayashi et al (1972) reported that 43 out of 51 patients who received operations to destroy their amygdala showed more normal social behaviour afterwards, including reduced aggression
- Gospic et al (2011)- some PPs subjected to mild provocation- when PPs reacted aggressively fMRI scans showed fast and heightened response by the amygdala
- a benzodiazepine drug (reduces arousal of the autonomic nervous system) taken before the provocation led to 2 effects- decreased activity of the amygdala and halved the number of rejections (reduced aggression)
Describe the role of the hippocampus in aggression
- involved in the formation of long-term memories
- This means that an animal can compare the conditions of a current threat with similar past experiences, so that they show an appropriate response (e.g., fear or aggression).
- Impaired hippocampal function may prevent the nervous system from putting things into a relevant and
meaningful context, and so may cause the amygdala to respond inappropriately to sensory stimuli, resulting in aggressive behaviour
Research evidence for the role of the hippocampus in aggression
Boccardi et al (2010)- found that habitually violent offenders exhibited abnormalities of hippocampal functioning
Limbic system diagram
Limbic system and aggression- strengths
Evidence for role of amygdala:
- Pardini et al (2014)
- longitudinal study of male PPs from childhood to adulthood
- some of 56 PPs received MRI scan at age of 26
- discovered that that lower amygdala volume were associated with higher levels of aggression and violence
- relationship remained even after the researchers controlled for confounding variables s
- suggests that the amygdala plays an important role in evaluating the importance of sensory information and that lower amygdala volumes compromises this ability and makes a violent response more likely
Evidence for role of hippocampus:
- Raine et al (2004)
- Provided support for the role of the hippocampus in aggressive behaviour
- Two groups of violent criminals
- One group acted impulsively, the other ‘cold calculating criminals’
- Criminals who acted impulsively had differing sizes of their hippocampus
- The asymmetry of their hippocampus impacts the ability of the amygdala and the hippocampus to work together
- Emotion information not processed properly, leading to inappropriate verbal and physical responses
Evidence to link limbic system to aggression:
- Sumer et al (2007)
- reported on case study of a 14yo girl, who following an MRI scan was diagnosed with a tumour in the limbic system
- investigated because she had been experiencing epileptic seizures and was behaving in very aggressive manner
- when the tumour was treated with drugs, the girls level of aggression returned to normal
- provides support for the idea that high levels of aggression could be linked to the limbic system
Limbic system and aggression- weaknesses
Other brain structures involved:
- limbic structures (e.g. the amygdala) function together with the orbitofrontal cortex (OFC) which is not part of the limbic system
- the OFC is convolved in impulse regulation and inhibition of aggressive behaviour
- Coccaro et al (2007)- OFC activity is reduced in those with psychiatric disorders that feature aggression
- this reduced activity disrupts the OFCs impulse control function, which in turn causes aggressive behaviour
- shows that the neural explanation of aggression is more complex than theories focusing on the amygdala suggest
Direct or indirect effects:
- some argue that neural factors are directly linked to agression- e.g. Gospic et als study of amygdala creativity and benzodiazepines supports
- however, the role of neural factors may be indirect as may be other factors that influence it
Exact role of amygdala unclear:
- whilst some studies suggest that lower amygdala volume/amygdala activity is associated with higher levels of aggression, others have found the opposite
- e.g. Muller et al (203)- showed 6 male psychopaths and 6 normal male controls a series of positive and negative pictures whilst having their brain activity monitored using and fMRI and found that psychopaths had increased activity in amygdala
Correlational research:
- most research looking at neural influences on aggression is correlational
- good ethical reasons because opportunities to experimentally manipulate brain structures are limited but when two variables are correlated, it is impossible to establish which one is the cause of the other, or if there is a third variable involved
Describe the role of serotonin in aggression
- neurotransmitter involved in communication of impulses between neurones
- studies have shown that serotonin in normal levels exerts a calming, widespread inhibitory effect on neuronal firing in the brain
- therefore, it is claimed that low levels of serotonin, particularly in the prefrontal cortex, remove this inhibitory effect resulting in individuals being less able to control their impulsive and aggressive responses (deficiency leads to loss of self-control and increase in impulsive behaviour incl. aggression- Denson e al 2012)
Research evidence for role of serotonin in aggression
Mann et al (1990):
- gave 35 healthy individuals dexfenfluramine which is known to deplete serotonin
- using a questionnaire to assess hostility and aggressive levels, found that dexfenfluramine treatment in males (but not females) was associated with an increase in hostility and aggression scores
Virkkuenen et al (1994):
- the major metabolite 5-HIAA (waste product) of serotonin tends to be low in the cerebrospinal fluid of violent impulsive and violent non-impulsive offenders
- significantly lower in impulsive offenders
Role of serotonin- strengths
Research evidence:
- Crockett et al (2009)
- used game playing and moral dilemmas to observe behaviours
- One group had their serotonin levels reduced by manipulation of their diets
- others had their levels increased by being administered an SSRI
- this was temporary change
- found PPs given restrictive diet displayed higher levels of retaliation against their opponents, and the PPs who had higher levels of serotonin responded to emotional moral dilemmas with increased compassion
- These results together suggest that low serotonin levels can induce aggressive responses
BUT could be argued that this study has low validity because game playing is not a direct physical aggressive response- It could be, for example, that there is no effect of serotonin when measuring actual aggression
Animal studies:
- Raleigh et al (1991)
- found that vervet monkeys fed on experimental diets high in tryptophan (which increases serotonin levels in the brain) exhibited decreased levels of aggression
- Individuals fed on diets that were low in tryptophan exhibited increased aggression behaviour, suggesting that the difference in aggression could be attributed to their serotonin levels
Criminal studies:
- Davidson et al (2000)
- suggested that serotonin may provide an inhibitory function i.e. high serotonin levels may lower aggressive behaviour
- When comparing violent criminals to non-violent ones, the levels of serotonin found in violent criminals were markedly lower
Practical applications:
- has been shown that increasing serotonin levels in both juvenile delinquents (Morand) and in institutionalised patients (Greenwald) reduces their aggressive tendencies.
- Therefore, this means that aggression and violence can be controlled for the benefit of society
Drug research:
- Drugs (e.g. paroxetine) that increase serotonin have been found t also reduce levels of aggressive behaviour
- Berman et al (2009) gave PPs either placebo or dose of paroxetine
- PPs then took part in a lab-based game that involved giving and receiving electrical shocks in response to provocation (e.g. insults)
- the paroxetine group consistently gave fewer and less intensive shocks than the placebo group
- this study is evidence of a causal link between serotonin function and aggression
Role of serotonin- weaknesses
Direct vs indirect effects:
- role of neural factors may be indirect
- e.g. Denson et al found link between serotonin and aggression
- however, this is an indirect link because other factors (e.g. social, psychological) may influence it
Correlational research:
- most research looking at neural influences on aggression is correlational
- good ethical reasons because opportunities to experimentally manipulate neurotransmitters are limited but when two variables are correlated, it is impossible to establish which one is the cause of the other, or if there is a third variable involved
Determinism:
- this view of human behaviour is very deterministic
- The link of aggressive behaviour to the reduction of serotonin in these criminals does not allow for the idea of free will
- This has an important implication in that perhaps violent criminals are not to blame for their actions as their serotonin levels are beyond their control
Name hormones associated with aggression
- testosterone
- cortisol
- progesterone
Describe the role of testosterone in aggression
- reliable observation that males more aggressive than females- attention on male sex hormone testosterone
- androgen responsible for the development of masculine features
- therefore found in much higher concentrations in males compared with females
- influences aggression in young adulthood onwards - has a role in regulating social behaviour via its influence on certain areas of the brain associated in aggression
- testosterone levels peak in young adult males [21-35]
- at this age there is an increase in male on male aggressive behaviour- (Daly and Wilson, 1998)
- changes in testosterone levels appear to influence aggressive behaviour by increasing a mcdelivery activity during the processing of social threats- e.g. angry facial expressions
Describe studies surrounding the role of testosterone in aggression
- castration studies of animals shows that removing the testes- the source of testosterone- reduces aggression in males of many species
- Giammanco et al (2005)- giving injections of testosterone to the same animals restores some aggressive behaviour
- Dolan et al (2001)- study of prison population of violent offenders- found positive correlation between testosterone levels and aggressive behaviours in a sample of 60 male offenders in UK maximum security hospitals- mostly had personality disorders, such as psychopathy, and histories of impulsively violent behaviour
Describe the role of cortisol in agression
- Van Goozen et al (2007)- claim link between aggression and the hormone cortisol
- purchased by the adrenal mitchele, important parts of bodies reaction to stress
- inversive correlation between cortisol and aggression- lower levels of cortisol are associated with higher levels of aggression
- also suggested that when cortisol is high, testosterones influence on aggression is blocked
Describe research studies into the role of cortisol in aggression
- studies have reported low levels of cortisol in habitually violent offenders
- Carre and Mehta (2011)- dual-hypothesis- suggests high levels of testosterone lead to aggressive behaviour but only when levels of cortisol are low- when cortisol high, testosterone influence on aggression blocked
Describe the role of progesterone in aggression
- some evidence that progesterone- female ovarian hormone- plays an important role in aggression in women
- levels of progesterone vary during the ovulation cycle and are lowest during and just after menstruation
- Ziomkiewicz et al (2012)- found a negative correlation between progesterone levels and self-reported aggression- suggests that low levels of progesterone are linked to increased aggression in women
Strengths of the hormonal mechanisms of aggression
Animal studies:
- Wagner et al (1970)- showed that if a male mouses castrated then overall levels of aggression tend to decrease
- if the castrated mouse receives testosterone injections, the aggression levels increase
- Giammanco et al (2005)- review of studies confirms role of testosterone- e.g. in male Rheus Monkeys, there is an increase in both testosterone levels and aggressive behaviour during the mating season
- in rats, castration of males reduces testosterone and also mouse killing behaviour, injecting female rats with testosterone increases mouse killing
- these findings show the role of testosterone in a range of animal species
COUNTERPOINT-
- research using non human animals must always be generalised to humans with care due to differences in Physiology
- Carre and Mehta’s findings concerning cortisol applied only to human aggression
- cognitive factors play a greater role in human aggression, especially in ‘cold blooded’ proactive aggression
- BUT- Potegal et al (1994)- states that humans aren’t known humans are more similar than dissimilar and so we should be able to generalise with confidence
Evidence from criminals:
- Dabbs et al. (1987)- measured salivary testosterone in violent and nonviolent criminals
- Those with the highest testosterone levels had a history of primarily violent crimes, whereas those with the lowest levels had committed only non-violent crimes
- Studies of non-prison populations have found similar trends
Research for cortisol:
- McBurnett et al (2000)- 4-year longitudinal study on 38 boys who had been referred to a clinic for problem behaviours
- found that the boys with lower cortisol levels (measured using saliva tests) exhibited three times the number of
aggressive symptoms compared with boys with higher levels
- They were also labelled as the most
aggressive and the ‘meanest’ by their peers
- supportes the link between low levels of cortisol and increased aggression
Dual-hormone hypothesis:
- Carre and Methas dual-hypothesis- see previous cards- suggests that combined activity of testosterone and cortisol may be a better predictor of aggression than either hormone alone
Weaknesses of the hormonal mechanisms of aggression
Inconsistent evidence:
- Despite many studies showing a positive relationship between
testosterone and aggression, others studies found no such relationship
- E.g. positive correlations have been reported between levels of testosterone and self-reported levels of aggression among prison inmates (Albert et al., 1994) and between testosterone levels and the likelihood of responding aggressively to provocation (Olweus et al, 1988)
- On the other hand, no correlation was found between testosterone and actual violent behaviour among male inmates in prison
- This suggests that the relationship between testosterone in humans is unclear
Name ways in which genetic factors in aggression are investigated
- Twin studies
- Adoption Studies
Outline the nature of twin studies for aggression
- researchers compare the degree of similarity for a particular trait (such as aggression) between sets of monozygotic (MZ) twins and dizygotic (DZ) twins
- If the MZ twins are more alike in terms of their aggressive behaviour, then this should be due to their genes rather than their environment (both types of twins share the same environment but MZ twins are more genetically alike)
Describe findings of twin studies into aggression
Several studies suggested that heritability account for about 50% of
the variance in aggressive behaviour:
Coccaro et al (1997)-
- studied adult male MZ and DZ
twins
- aggressive behaviour (direct physical assult- concordance rates of 50% for MZ twins and 19% for DZ twins
- corresponding figure for verbal aggression- 28% (MZs) and 7% (DZs).