Neural and Hormonal Explanations of Aggression

• What are neural mechanisms related to

  The nervous systemm
• what are hormonal mechanisms related to

  the endocrine system
• What is the limbic system

  • What did Papez and Macclean link it to?

  It's a key structure/region in the brain

  • Papez and Macclean linked it to having invlovment in aggressive behaviours
• What is the role of the amygdala 


  It generates emotions and attaches them to stimuli, then storing it in the emotional memory.
• What are the differences between a hyperactive and hypoactive amygdala in offenders

  Hyperactive: reactive aggression

  Hypoactive: other offenders (e.g. psychopaths)
• What type of amygdala response causes aggressive reactions

  Hyperactive - a fast and heightened response
• AO1/AO3: Potegal (1996): research into the amygdala and aggression

  Found that: IN HAMSTERS

  • stimulation of the amygdala increases aggression
  • Leisioning (e.g. preventing its function) reduces aggression
• AO1/AO3: Groves and Schlesinger: research into the amygdala

  Found that surgical removal of the amygdala reduced human aggression in previously violent individuals

  • This establishes a cause and effect relationship between the function of the amygdala and aggression
• AO1/AO3 (SUPPORTING): Charles Whitman Case Study

  Charles Whitman killed many people in Austin - the morning of he also killed his mother and wife

  • Post mortem revealed a tumor growing that compressed the amygdala and also compressed the hypothalamus

  THIS SHOWS THE LINK BETWEEN THE ROLE/PROPER FUNCTIONING OF THE HYPOTHALAMUS/AMYGDALA AND AGGRESSIVE BEHAVIOUR
• what are the 2 functions of the hypothalamus

  1: responsible for behaviours such as hunger and thirst as well as maintenance of basal body temperature (i.e. homeostasis)

  2: responsible for motivational behaviour and controls the pituitary gland (the master gland) that controls all other glands in the endocrine system

  THE HYPOTHALAMUS THEREFORE PLAYS A KEY ROLE IN CONNECTING THE ENDOCRINE SYSTEM TO THE NERVOUS SYSTEM
• AO1/AO3: Flynn (2006): research into the hypothalamus and aggression

  IN CATS

  lateral stimulation: predatory aggression (catching and killing silently and quickly)

  medial stimulation: rage aggression (arching back, hissing, baring teeth etc)

  THIS SUGGESTS THAT DIFFERENT TYPES OF AGGRESSION ARE CONTROLLED BY DIFFERENT AREAS OF THE BRAIN AND SUPPORT THE EFFECTS OF THE HYPOTHALAMUS ON AGGRESSION
• WHAT EVALUATION POINT CAN WE USE FOR POTEGAL AND FLYNN

  ANIMAL STUDIES - GENERALISABILITY

  • humans have more complex structures of cerebral cortex (decision making) - therefore they may be able to control aggression whereas animals act upon instinct.
  • social + legislative norms that make prevent aggression behaviour due to reprocussion
• What is the role of serotonin (Cases 1995)

  Serotonin is an inhibitory neurotransmitter which is associated with a greater degree of self control due to the calming effect it has on the brain

  Cases (1995) - it reduces neuronal firing in the brain
• What are normal levels of serotonin in the orbitofrontal cortex associated with

  normal levels of serotonin in the orbitofrontal cortex inhibit neurons (reduce action potentials + firing)

  • normal levels are therefore associated with a greater degree of self control
• What happens if there are low levels of serotonin in the brain

  Low levels remove the inhibitory effect the neurotransmitter has in normal brains

  • people are therefore less able to control impulsive and aggressive behaviour
• What effect does serotonin have on the amygdala (and as a result on aggressive behaviour)

  Serotonin typically inhibits the firing of the amygdala, meaning it controls aggressive impulses (because a hyperactive amygdala has been linked to reactive aggression)
• AO1/AO3: Research into serotonin and aggression (amino acids)

  Serotonin is manufactured from the amino acid: tryptophan

  Research on Vervet Monkeys (AO3 point: animal studies) showed that:

  • reducing levels of serotonin resulted in an increased level of aggressive behaviour
  • however, feeding a diet rich in tryptophan resulted in a decrease in aggression (e.g. nuts)
• What is testosterone

  an androgen + male primary sex hormone
• what are hormones

  chemical messengers that regulate and control body functions - they are secreted from glands directly into the bloodstream
• What led to testosterone being a consideration as a factor linked to aggression

  Males are generally more aggressive than females

  • Testosterone is responsible for the development of masculine features and plays a role in regulating social behaviour (incl. aggression) via its influence on certain areas of the brain associated with aggression
• AO1/AO3: Support for testosterone and aggression: Dolan et al (2001)

  Dolan found a positive correlation between testosterone and aggression in male offenders with a history of violent and impulsive behaviour

  AO3: correlational studies - not cause and effect
• AO1/AO3 supporting testosterone and aggression: Berthold (1859): leg horn cockrels

  Berthold transplanted testes into castrated male birds and observed that the aggression levels increased (testosterone is secreted from the testes)

  • this establishes a relationship between testosterone and aggression
• AO3: Weakness: animal studies + generalisability to humans

  Mammalian brain systems are different to animals - even primates due to the structural differences in the cerebral cortex (which is responsible for functioning + emotional regulation)

  • This means that tests on animals can’t be generalised to humans as there are structural differences in the brain that may lead to different outcomes
• AO3: counterpoint to animal studies using the 41 psychopaths study

  C/P: The study done on the 41 psychopaths that displayed the imbalance in activity beteen the right/left hemisphere shows the same findings when the study was repeated on animals.

  less activity on the left, more on the right compared to 41 controls

  • This shows that animal studies and human study findings are consistent and this improves the validity of using animal studies to generalise to humans.
• AO3: Weakness: Biological Reductionism

  These studies reduce behaviour to a single function (the brain and biology) and fails to consider the role of society upon our behaviour.

  • It only attributes aggression to biology which may not be a holistic explanation of aggression
  • This means that the biological approach towards aggression may lack some reliability as it fails to account for the environment and the role of environmental learning which we know plays a role in our behaviour due to research evidence and social-psychological theories such as SLT and Frustration Aggression Hypothesis
• AO3: Strengths: research support increases reliability

  Research studies with similar findings increase the reliability and validity of findings.

  • This is because if cross-study results are similar, this strengthens the theory as the trend in results remains consistent and displays findings are more widespread and not due to PPT variables.

  This improves the validity of findings and results and means our conclusions have better support to be generalisable.
• AO3: Weakness: Human studies fails to display cause and effect

  For example Dolan et al found that there is a correlation between high testosterone levels and aggression in males with a history of impulsive violent behaviour.

  • This however is only a correlational study as this is because it would be unethical to manipulate human brains as it could create a lasting impact.

  This means that because variables can't be isolated, we can't be sure of the effect it may have.
• AO1/AO3: Berman, Gladue and Taylor: Reaction Time + shocks

  asked male PPT's to take part in a reaction time competition where they could set the shock level given to the losing competitor (the level of shock was recorded as aggression)

  • A relationship was found between salivary testosterone levels and aggression
  • higher T = higher agg.
• AO3: Counterpoint to Berman, Gladue and Taylor by Mazur (EVOLUTIONARY APPROACH)

  We should distinguish between dominance behaviours and aggression.

  • Dominance is intended to gain or maintain status (evolutionary) and acting aggressivley is one way of getting there
  • The evolutionary explanation would say this is a result of psychological mechanisms: anti-cuckoldry behaviours (mate retention strategies) that have evolved due to them aiding in survival of the fittest and natural selection

  This would suggest that the aggressive behaviour was a nautral instinct to 'show who's boss'
• AO3: Strength: Real world Application

  Research into the neural mechanisms of aggression + the impact of serotonin on the limbic system gave rise to the use of SSRI's and other drugs to act on neurotransmitters and reduce aggressive drives

  • This has real world implications as it can significantly improve quality of life for individuals
• AO1/AO3: Research into the limbic system and aggression

  PET scans of 41 psychopaths + 41 controls

  • found an imbalance of activity between left and right hemispheres in the limbic system in psychopaths (specifically amygdala and hypothalamus).
  • left = less activity
  • right = more activity

  These are associated with aggression in animals, now we have human evidence to support this
• What role did the research into the limbic system using the 41 psychopaths play in strengthening the use of animal studies

  The findings between animal studies and human studies were consistent.

  • This supports the use of animal studies due to the similarities in findings - this shows they have important and valid use in neural research