Neural and hormonal mechanisms

• What is Aggression?

  An act carried out with the intention to harm another person physically or psychologically
• What are the two types of aggression?

  • Proactive
  • Reactive
• What is proactive aggression?

  • 'Cold blooded'
  • Planned method
• What is reactive aggression?

  • 'Hot blooded'
  • Angry and impulsive
  • Accompanied by psychological arousal
• What is the Limbic system?

  • Subcortical structures in the brain
  • Thought to be closely involved in regulating emotional behaviour including aggression
• Which brain structures are apart of the limbic system?

  • Amygdala
  • Hypothalamus
  • Hippocampus
• What does the Amygdala do?

  • Responsible for attaching emotional significance to sensory information
  • Responsible for how we respond to threats and challenges
  • How reactive it is has been shown to be a predictor of aggressive behaviour
  • Fight or Flight
• What does the Hippocampus do?

  • Forms long term memories
  • Allows individuals to compare current threat conditions with past experiences
  • If a person is attacked the next time they are in a similar situation they are more likely to respond with aggression
• What does the hypothalamus do?

  • Responsible for the regulation of the autonomic nervous system
  • ANS regulates responses to emotional circumstances
  • Damage or ANS not regulating = Inappropriate response to perceived threats
• What do FMRI scans do?

  • Measures brain activity while someone is performing a task
  • Detects areas of the brain that are rich in oxygen and thus are active
• Describe Gospic et al's study:

  • Participants had brain activity scanned using an FMRI whilst playing the ultimatum game
  • When responders were given an unfair offer there was a fast heightened reaction in the amygdala and offer was rejected
  • Can be seen as aggressive act towards a social provocation
  • Also it was found that when participants were given benzodiazepine, which reduces amygdala activity, rate of rejection dropped
• What is Serotonin?

  • Neurotransmitter
  • Has a major influence on mood, impulsivity, and behaviour
  • Has an inhibitory effect on neurons
• Describe the role of serotonin in aggression:

  • Reduced serotonin activity in the prefrontal cortex is related to reduced self control / disinhibition
  • Normal levels of serotonin inhibits activity in the orbitofrontal cortex - Leads to greater self control of behaviour
  • If serotonin levels are too low then the part of the brain becomes overactive - results in more impulsive behaviours including aggression
• Supporting Evidence - Matti Virkkunen et al:

  • Compared levels of a serotonin breakdown product in the cerebrospinal fluid of violent impulsive and violent non-impulsive
  • Levels were significantly lower in the impulsive offenders
  • They also suffered more sleep irregularities
  • Disturbance in sleep pattern strongly implies disruption of serotonin function
• Supporting Evidence - Berman et al:

  • Lab experiment
  • Participants given choice to give electric shocks to each other in response to a provocation
  • Independent groups design
  • Half the participants were given paroxetine (SSRI) and half were given a placebo
  • Paroxetine group gave fewer shocks than placebo group
  • Supporting the link between serotonin and aggression

  COUNTERPOINT - Highly controlled and in lab environment so unable to generalise findings
• What is testosterone?

  • It is a hormone from the androgen group produced mainly in male testes (smaller amounts in women's ovaries)
  • Responsible for development of masculine features and associated with aggression
• How does testosterone impact aggression?

  • 10 - 40x stronger in men than women
  • Has a role in regulating social behaviour
  • Higher than normal levels increases reactivity of the amygdala
• Supporting Evidence for Testosterone - Wagner:

  • Castrated mice
  • Testosterone is the sex hormone in males so castration stops its production
  • Found that castrated mice became less aggressive
  • Aggression increased when the mice were injected with testosterone
• Limitations of Wagner's study:

  • It was only carried out on animals so results can't be generalised to humans
• Supporting Evidence for Testosterone - Dolan et al:

  • Found a positive correlation between testosterone levels and aggressive behaviours in a sample of 60 offenders in a UK max security hospital
  • The men had histories of impulsively violent behaviour and mostly suffered from personality disorders
• limitation of research into testosterone:

  • Some researchers show other hormones as involved
  • Carre and Mehta
  • Dual-hormone hypothesis
  • High testosterone leads to aggression when only when cortisol is low
  • When cortisol is high it blocks testosterones influence on aggressive behaviour