Aggression Flashcards
What is the limbic system?
An area of the brain which controls basic emotions and drives
State the two structures of the limbic system associated with aggression
- The amygdala
- The hippocampus
Describe the role of the amygdala in aggression
- The amygdala is responsible with evaluating the emotional importance of sensory information and producing an appropriate response
- If the amygdala is stimulated electrically the animal responds with aggressive behaviour
- If it is removed the animal no longer responds aggressively
What did Kluver and Bucy find regarding the amygdala’s role in aggression?
The destruction of the amygdala in dominant monkeys causes it to lose its dominant place in the social group
Describe the role of the hippocampus in aggression
- The hippocampus is involved in the formation of long-term memories
- This allows the animal to compare a current threat to past experiences to produce an appropriate response
- Impaired hippocampal function prevents the nervous system from putting situations into a meaningful context
- This may cause the amygdala to respond inappropriately, often with aggression
What did Boccardi find?
Habitually violent offenders exhibited abnormalities of hippocampal functioning
What neurotransmitter is associated with aggression?
Serotonin
Describe the role of serotonin in aggression
- Known as the serotonin deficiency hypothesis
- Normal levels of serotonin exerts an inhibitory effect on the firing of the amygdala
- Low levels of serotonin remove this inhibitory effect
- This leads to the overfiring of the amygdala
- Individuals are less able to control impulsive and aggressive behaviour
Which hormone is associated with aggression?
Testosterone
What is Testosterone?
- A hormone which produces male characteristics
- Levels peak in young males
- Thought to influence aggression from young adulthood
What did Sapolky find with regards to testosterone?
That removing the source of testosterone in different species resulted in lower levels of aggression
Describe the effect of testosterone on aggression using research evidence
- Dabbs found that men tend to have testosterone in higher concentrations than women and tend to be more aggressive
- Davy and Wilson found that at an age when testosterone levels are highest (21-35) there is an increase in male-on male aggressive behaviour
How does testosterone lead to more aggressive behaviour?
Changes in testosterone increase amygdala reactivity during the processing of social threat
Evaluate neural/hormonal influences on aggression
Evidence for the role of the amygdala- Pardini et al found reduced amygdala volume leads to more aggression. Longitudinal study of male participants. 56 p’s with varying violent histories had MRI scans at age 26 and it was found that those with lower amygdala volumes showed more aggressive and impulsive behaviour. This shows the amygdala is important
Evidence for the role of the hippocampus- Raine et al looked at two groups of violent criminals- some had been caught and some not. The unsuccessful ones were assumed to be acting more impulsively and MRI scans of their brains showed an asymmetrical hippocampus. This could have impaired the ability of the amygdala and hippocampus to work together.
Research support for the serotonin deficiency hypothesis- Raleigh et al fed vervet monkeys on diets high in tryptophan which increases serotonin levels and found reduced aggression. Diets low in tryptophan resulted in more aggression.
Inconsistent evidence for role of testosterone- Positive correlations have been found between levels of testosterone and self-reported levels of aggression among prison inmates but no such relationship has been found between testosterone levels and actual violent behaviour. This suggests the relationship remains unclear
How are twin studies used to investigate genetic influences on aggression?
- Monozygotic twins share 100% of their DNA and dizygotic twins share 50% of their DNA
- Researchers look for degrees of similarities between twins (concordance rates)
- If monozygotic twins show high concordance in aggressive traits we can assume its genes rather than the environment
What did Coccaro et al find?
- In adult twins, 50% of the variance in direct aggressive behaviour was due to genes
- Since this was not 100% it means other factors must be involved
How are adoption studies used when researching genetic influences in aggression?
- If a positive correlation is found between the adopted child and their biological parents, it suggests the role of genetics
- If a positive correlation is found between the adopted child and their adopted family, it suggests the role of the environment
Describe an adoption study and what it found in regards to genetics in human aggression
- Hutchings and Mednick
- Found a significant number of criminal adopted boys had (biological) parents with criminal convictions
- This supports the role of genetics
Describe Rhee and Waldman’s study and findings
- Meta analysis of 51 twin and adoption studies
- Concluded that aggressive anti-social behaviour was largely a product of genetic contributions
- However extraneous variables such as age and method of assessment have impacted the influence of aggression
- This shows that although genetics is important, other factors affect how it is expressed
What is the MAOA gene?
- A gene responsible for producing the enzyme MAOA
- MAOA is responsible for the metabolism of serotonin in the brain
- Low levels of serotonin are associated with impulsive and aggressive behaviour
- Low levels of MAOA has been associated with aggressive behaviour
Describe Brunner et al’s research
- Studied 5 generations of a Dutch family
- Many male members demonstrated violent and aggressive behaviour
- These men were found to have had abnormally low levels of MAOA and a defect in the gene
What is the MAOA-L gene?
- Challenge to MAOA
- Common in populations where there has been a history of warfare
- Known as the ‘warrior gene’
- Participants with MAOA-L displayed higher levels of aggression
Evaluate genetic factors in aggression
Difficulties in determining the role of genetic factors- more than one gene contributes to a behaviour, there may be environmental influences and these influences may interact with each other
Problems of assessing aggression- many studies of aggression are reliant on self-reports/ parental reports. Findings not consistent with observational ratings
Evidence for the influence of the MAOA gene- Tiihonen studied Finnish prisoners and found the MAOA-L gene and another gene were associated with extremely violent behaviour. No evidence of this in non- violent offenders
MAOA gene explains gender differences- MAOA gene is associated with the X chromosome. When men inherit an X from their mother, it is more likely to affect them than women who are inheriting the same gene so remain unaffected. This could explain why men are more aggressive.
What are ethological explanations?
- State that members within the same species have an innate, unlearned set of behaviours
- These innate behaviours are called fixed action patterns (FAPs)
What is a FAP?
A series or sequence of acts that occur behaviourally in animals
What do FAPs occur in response to?
A sign stimulus which is the essential feature of a stimulus necessary to elicit a response
What produces a FAP?
A neural network called the innate releasing mechanism which communicates with motor control circuits to release the FAP associated with the sign stimulus
Give an example of a FAP
- Red-bellied stickleback fish
- Males turn red during mating season
- They are naturally aggressive towards other red-bellied sticklebacks
- Anything that is red will bring about this response
- Once the FAP is initiated it will run until completion
- The sign stimulus is the presence of a red underbelly rather than another male
Evaluate ethological explanations of aggression
Criticisms of the ‘instinctive’ view- Lehrman believed that Lorenz had underestimated the role of environmental factors which interact with innate factors in complex ways. ‘Behavioural pattern’ is a better term for FAP since it reflect that these are not simply innate and can be modified by experience
Human FAPs- Eibl-Eibesfeldt found some universal human FAPs such as smiling. However aggression was suggested to no longer be adaptive due to our ever changing environment. The flexibility of human behaviour has proved more effective than stereotypical, fixed patterns of behaviour.
Benefits of ritualised aggression- prevents conflicts from escalating into dangerous aggression. Chagnon found the Yanonmamo people use chest pounding and club fighting to settle disputes. This reduces actual aggression and prevents serious injury/ death
Killing conspecifics is not rare- ethological explanations suggest that the only way that an animal can kill another animal of the same species is by accident. However it has been found that lions kill off cubs of other lions and chimpanzees will kill off other members of the group which shows its more systematic. This casts doubt on the claim that animal aggression is more ritualistic than real
What is the evolutionary explanation of aggression?
Suggests aggression is an adaptive behaviour passed down from our ancestors
What kind of problems did aggression solve for early humans?
- Gaining resources
- Intimidating or eliminating male rivals for females
- Deterring mates from sexual infidelity