The Role of Neural and Hormonal Mechanisms in Aggression



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The Role of Neural and Hormonal Mechanisms in Aggression

  • To understand how destroying the amygdala reduces aggression.
  • Explain how testosterone leads to aggressive behaviour.

Is aggression

  • Nature or nurture?

Phineas Gage

  • One of the best examples of how brain injury can influence aggressive behaviour is the case of Phineas Gage.
  • 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.
  • He survived the accident, but his personality was changed, including a huge increase in aggression.
  • *@!* off, I’ve got a splitting headache!

Neural Mechanisms – Brain structure

  • Organised hierarchically and moderated by the pre-frontal cortex.

The Role of the Amygdala

  • Kluver-Bucy syndrome – taming effect found in rhesus monkeys by removing part of the temporal lobes and therefore destroying the amygdala.
  • Narabyashi et al (1972) – 43 / 51 patients whose amygdala was destroyed through psychosurgery showed reduced aggression afterwards.

Mark & Ervin (1970) – case study of female patient behaviour following electrical stimulation of amygdala.

  • Mark & Ervin (1970) – case study of female patient behaviour following electrical stimulation of amygdala.
  • She exhibited facial grimacing, became very angry and flung herself at the wall.
  • Ashford (1980) – temporal lobe epileptics often become aggressive, attacking furniture and people.

The Role of Neurotransmitters

  • The neurotransmitter serotonin influences aggressive behaviour.
  • In research with vervet monkeys, reducing serotonin levels resulted in increased aggressive behaviour, whereas increasing serotonin decreased the aggressive occurrences.
  • Drugs to raise serotonin levels, such as trytophan have been given to juvenile delinquents and unpredictable institutionalised patients.
  • The relationships found here are CORRELATIONAL. What are the weaknesses of correlational research?
  • So… the higher the serotonin level, the lower the aggression.
  • 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.

The Role of the Prefrontal Cortex

  • Regulates the emotional responses driven by the amygdala.
  • Damage to prefrontal cortex results in impulsivity, immaturity and loss of control.
  • Anderson et al (1999) – damage during infancy related to aggressive behaviour as adults.
  • Case studies comparing early onset damage with adult onset damage to frontal lobes.
  • Early onset patients also performed poorly on tests of moral and pro-social reasoning.
  • This brings in a cognitive element also then. Remember to think ‘approaches’ at all times!

Raine et al (1997) – investigated brain activity of 41 murderers using PET scans.

  • Raine et al (1997) – investigated brain activity of 41 murderers using PET scans.
  • Found reduced glucose metabolism in prefrontal cortex, suggesting this brain area is less active than in normal controls.
  • Volkow et al (1995) found violent psychiatric patients had reduced cerebral blood flow to prefrontal cortex.
  • 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.

GENETIC

  • What have animal studies shown about the possibility that aggression is inherited?
  • What have concordance studies shown?
  • What have adoption studies shown?
  • Now try the gap fill exercise

Using the cut and stick activity

  • Match up the images to the keywords on the display paper and then link them to how they would cause aggression.

NEURAL AND HORMONAL EXPLANATIONS

  • NEUROTRANSMITTERS
  • Serotonin – low levels associated with aggression
  • Dopamine – high levels associated with aggression
  • Antidepressants and antipsychotic drugs reduce levels of aggression (treatment-aetiology fallacy?/cause & effect?)
  • HORMONES
  • Testosterone – link between levels and aggression
  • Animal research
  • Sex change individuals
  • Prison populations

BRAIN STRUCTURE

GROUP DISPLAY

  • Why might to aggression in groups have been adaptive?
  • Humans still use group display:
  • WAR
  • FOOTBALL FANS
  • LYNCHINGS

Hormones and Aggression - Testosterone

  • Beeman (1947) castrated male mice and found that aggressiveness reduced.
  • He later injected the mice with testosterone which re-established their aggressiveness.
  • Castration has since been used as a method for making domestic and farm animals more manageable.

Testosterone is also clearly related to aggression in humans.

  • Testosterone is also clearly related to aggression in humans.
  • 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.
  • 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.
  • But remember these are correlations and what do we know about correlations?..

The same effects of testosterone are also found in women.

  • The same effects of testosterone are also found in women.
  • Dabbs et al (1988) – female prisoners. Testosterone highest in cases of unprovoked violence but lowest where violence was defensive (eg. In domestic abuse cases)
  • 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.

Using the information, create a table of evidence for and against hormones as the cause of human aggression

  • Using the information, create a table of evidence for and against hormones as the cause of human aggression


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