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1. The Role of Neural and Hormonal Mechanisms in Aggression 2. Phineas Gage <ul><li>One of the best examples of how brain injury can influence aggressive…
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  • 1. The Role of Neural and Hormonal Mechanisms in Aggression
  • 2. Phineas Gage <ul><li>One of the best examples of how brain injury can influence aggressive behaviour is the case of Phineas Gage. </li></ul><ul><li>Working on a railway in 1848, he had an accident in which a tamping iron went up through his face , behind his left eye and out through the top of his head. </li></ul><ul><li>He survived the accident, but his personality was changed, including a huge increase in aggression. </li></ul>*@!* off, I’ve got a splitting headache!
  • 3. Neural Mechanisms – Brain structure <ul><li>Normal aggressive behaviour is not dependent on separate brain structures, but interaction of a system of structures. </li></ul>Organised hierarchically and moderated by the pre-frontal cortex.
  • 4. The Role of the Amygdala <ul><li>Kluver-Bucy syndrome – taming effect found in rhesus monkeys by removing part of the temporal lobes and therefore destroying the amygdala. </li></ul><ul><li>Narabyashi et al (1972) – 43 / 51 patients whose amygdala was destroyed through psychosurgery showed reduced aggression afterwards. </li></ul>
  • 5. <ul><li>Mark & Ervin (1970) – case study of female patient behaviour following electrical stimulation of amygdala . </li></ul><ul><li>She exhibited facial grimacing, became very angry and flung herself at the wall. </li></ul><ul><li>Ashford (1980) – temporal lobe epileptics often become aggressive, attacking furniture and people. </li></ul>
  • 6. Muller et al (2003) showed 6 male psychopaths and 6 male controls a series of positive and negative pictures whilst in MR scanner. Found increased activity in the amygdala. The exact role of the amygdala in aggression is unclear, but it is certainly a significant one. Research suggests an interaction between the amygdala and the pre-frontal cortex.
  • 7. The Role of the Prefrontal Cortex <ul><li>Regulates the emotional responses driven by the amygdala. </li></ul><ul><li>Damage to prefrontal cortex results in impulsivity, immaturity and loss of control. </li></ul><ul><li>Anderson et al (1999) – damage during infancy related to aggressive behaviour as adults. </li></ul><ul><li>Case studies comparing early onset damage with adult onset damage to frontal lobes. </li></ul><ul><li>Early onset patients also performed poorly on tests of moral and pro-social reasoning. </li></ul>This brings in a cognitive element also then. Remember to think ‘approaches’ at all times!
  • 8. <ul><li>Raine et al (1997) – investigated brain activity of 41 murderers using PET scans. </li></ul><ul><li>Found reduced glucose metabolism in prefrontal cortex, suggesting this brain area is less active than in normal controls. </li></ul><ul><li>Volkow et al (1995) found violent psychiatric patients had reduced cerebral blood flow to prefrontal cortex. </li></ul> During the 1940s, frontal lobe lobotomies were performed with startling regularity ; partly because of the ‘calming’ effect on patients with a range of mental health problems – from depression to ADHD to OCD.
  • 9. The Role of Neurotransmitters <ul><li>The neurotransmitter serotonin influences aggressive behaviour. </li></ul><ul><li>In research with vervet monkeys, reducing serotonin levels resulted in increased aggressive behaviour, whereas increasing serotonin decreased the aggressive occurrences. </li></ul><ul><li>Drugs to raise serotonin levels, such as trytophan have been given to juvenile delinquents and unpredictable institutionalised patients. </li></ul>The relationships found here are CORRELATIONAL. What are the weaknesses of correlational research? So… the higher the serotonin level, the lower the aggression.
  • 10. Hormones and Aggression - Testosterone <ul><li>Beeman (1947) castrated male mice and found that aggressiveness reduced. </li></ul><ul><li>He later injected the mice with testosterone which re-established their aggressiveness. </li></ul><ul><li>Castration has since been used as a method for making domestic and farm animals more manageable. </li></ul>
  • 11. <ul><li>Testosterone is also clearly related to aggression in humans. </li></ul><ul><li>Dabbs et al (1995) – measured testosterone in saliva of 692 adult male prisoners. Found higher levels in rapists and violent offenders than in burglars and thieves. </li></ul><ul><li>Dabbs et al (1996) – looked at 12 fraternities in 2 universities. Members of fraternities with highest levels of testosterone were described as boisterous and macho, those with lowest were attentive and helpful. </li></ul>Those frat boys at it again… But remember these are correlations and what do we know about correlations?..
  • 12. <ul><li>The same effects of testosterone are also found in women. </li></ul><ul><li>Dabbs et al (1988) – female prisoners. Testosterone highest in cases of unprovoked violence but lowest where violence was defensive (eg. In domestic abuse cases) </li></ul>Other research has found conflicting results, but this is to do with the operationalisation of ‘aggression’. Think MAID now – (methods, approaches, issues, debates) Working in pairs, come up with as many points as you can.
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