what are the neural mechanisms in aggression?
the limbic system and serotonin
what is the limbic system?
connects the brain stem and the cortex
has the amygdala
controls a range of emotional behaviours
what is the role of the amygdala?
quickly evaluates the emotional importance of sensory information and promoting an appropriate response
what did Pardini et al find
participants with smaller amygdalas showed higher levels of aggression
what did ervin study and find?
case study of female patient
electrically stimulated her amygdala
she became very angry and flung herself at a wall
atypical female
what is kluver and bucy find?
that destroying the amygdala in aggressive monkeys, resulted in less aggressive behaviour
what study was done using fmri scans on the limbic system?
ps had their brains scanned while playing a game where they could reject or accept an offer of money. heightened activity in the amygdala when they rejected money because they thought it was unfair
What also operates with the amygdala?
the orbitofrontal cortex
what does the orbiofrontal cortex do?
regulates emotional responses driven by the amygdala
damage results impulsivity and loss of control
What did Raine et al find?
investigated brain activity in 42 murderers using PET scans.
abnormal activity in the amygdala and reduced glucose metabolism in the orbitofrontal cortex
What is serotonin?
a neurotransmitter involved in the communication of impulses between neurons
What are normal levels of serotonin associated with?
greater behavioural control and it typically inhibits the firing of the amygdala system
what are low levels of serotonin associated with?
low behavioural control, impulsivity and aggression
what is tryptophan?
increases serotonin levels in the brain
What did Rayleigh study and find?
gave different diets to monkeys
the monkeys who diet was high in tryptophan showed decreased levels of aggression
what did Passamonti find and study?
manipulated tryptophan levels in participants diets
ps given questionnaire to asses their aggressive tendencies
fmri scans to measure reaction to facial expressions
on low serotonin days, communication was weaker
practical application of research into serotonin
diets to easier serotonin levels such as tryptophan could be given to juvenile delinquents in order to calm aggressive tendencies
How have high levels of serotonin been associated with aggression?
dukes et al found a relationship
What is testosterone?
an androgen secreted by the testes.
Testosterone
Research for (mice)
Wagner- catstrated mice and aggression reduced, later injected them with testosterone which re-established their aggression.
Testosterone
Research for (species)
Increasing testosterone caused greater aggressive behaviour in several species and reducing it had the opposite effect.
Testosterone
Research for (prisoners)
Dabbs- measured testosterone levels in 692 adult male prisoners, higher levels were found in violent offedners compared to non-violent offenders.
Found a similar effect in women prisoners.
Testosterone
Research against (Dual-hormone hypothesis)
high levels of testosterone lead to aggresive behaviour when cortisol levels are low.
Evaluation of testosterone
Aggression or dominance?
Studies show that testosterone doesnt necessarily increase aggression but increases status-seeking behaviour, which is not intended to cause harm.
What does genetic theory say about aggression?
that genes are the cuase of aggressive behaviour.
Genetic factors
Research for (mice)
Lab selective breeding study.
Isolated a group of mice in order to identify mice more prone to aggression.
interbred the aggressive mice, after 19 generations, rates of aggression were 10x higher than in the controls.
the aggressive mice had heavier testes and forebrains and altered levels of serotonin and noradrenaline.
Genetic factors
Research for (twin and adoption studies)
Coccaro used a questionnaire to measure hostility in male participants.
they found concordance rate of 50% for MZ twins and 19% for DZ twins.
Rhee and Waldman- meta-analysis of adoption studies, found genetic influences account for 41% of the variation of aggression.
Genetic factors
The MAOA Gene
This gene is responsible for regulating the enzyme MAOA, which breaks down the neurotransmitters serotonin, noradrenaline and dopamine. This allows neurons to commincate more effectively.
Genetic factors
What does reserch suggest about the MAOA Gene
that the MAOA-L version predisposes a peron to violence.
Genetic Factors
What did Brunner research?(Dutch family)
Male members of this family had been particulary aggressive, the males were found to have the rare mutated version of the MAOA gene.
Genetic factors
Research for the MAOA gene (chilli sauce)
Mcdermott- those with the MAOA-L gene were more likely to force someone to eat chilli sauce, than someone with the MAOA-H gene.
Genetic factors
Research for the MAOA gene (Finland)
Studies prisoners in Finland, found severly violent prisoners had the MAOA-L gene in comination with the CDH13 gene.
Genetic factors
Rearch for MAOA gene (childhood influences)
Capsi studied 500 male children and looked at their anti-socail behaviour and found that the MAOA-L gene was invloved in aggression, but only if they had been maltreated as children.
suggestes an interactionist approach.
Genetic factors
The warrior gene
Research found that the MAOA-L gene is much more frequent in New Zealand Maori populations with a history of warfare than western populations.
Socially sensitive.
