AGGRESSION

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NEURAL AND HORMONAL MECHANISMS IN AGRESSION 

Neural Mechanisms:

  • Reactivity of limbic system predicts aggressive behaviour

Papez and Maclean identified the limbic system as: cingulate gyrus, septal area, hypothalamus, fornix, amygdala, parts of hippocampus and thalamus

- Amygdala is most important of these structures - plays key role in how humans and animals asses and respond to environmental threats and challenges

  • Amygdala is strongly associated w/aggression

- There's a strong association between aggression and amygdala activity, as supported by Gospic et al's Ultimatium game study

* Lab based game designed to provoke aggression

* fMRI brain scans carried out on pps

* Scans revealed agg reactions associated w/a fast and heightened amygdala response

 Benzodiazepine drug (reduces arousal of autonomic nervous system) taken b4 game halved no.of agg reactions and decreased amygdala activity

  • LOW levels of serotonin results in reduced self-control and increased agg

Normal levels of serotonin in orbitofrontal cortex have inhibitory effects - linked with reduced firing of neurons which is associated with greater behavioural self control

Decreased serotonin may disturb this mechanism, reducing self control and increasing impulsive behaviours (Denson et al)

Virkkunen et al

compared levels of serotonin metabolite (breakdown by-product) called 5-HIAA in the cerebrospinal fluid of violent impulsive and violent non-impulsive offenders

levels were significantly lower in impulsive offenders also suffered more sleep irregularities - (relevant as serotonin regulates sleep patterns)

Hormonal Mechanisms:

  • Testosterone is higher in men and so linked to aggression

- Testosterone = hormone repsonsible for development of masculine features - also regulates social behvaiour via its influence on areas of the brain involved in aggression

Giammanco et al's animal studies show experimental increase in testosterone are related to greater agg behaviour in several species ( castration studies (testosterone decrease) = decrease in agg)

  • Evidence for an association between testosterone and agg in humans from studies of prison populations (e.g. violent offenders)

Dolan et al found a positive correlation between testosterone levels and agg behaviours in a sample of 60 male offenders in UK max security hospitals

* These men mostly suffered from personality disorders - e.g. psychopathy - and had histories of impulsively violent behaviour

EVALUATION

Strengths 

  • Research support showing that drugs which increase serotonin activity also reduce levels of agg behaviour
  • Berman et al found pps given paroxetine (serotonin enhancing drug) consistently gave fewer and less intense electric shocks to a confederate group than people in a placebo group 
  • Wasn't only true of pps with history of agg behaviour but this study is useful evidence of a link between serotonin function and agg, going beyond usual correlational findings

Limitations

  • Limbic system explanation excludes other possibilities
  • Recent studies show that the amygdala functions in tandem with the OFC, which is NOT part of limbic system
  • OFC is involved in self-control, impulse reg and inhibition of agg behaviour
  • Coccaro et al showed OFC activity is reduced in patients w/psychiatric disorders that prominently feature agg - this disrupts amygdala's impulse-control function and

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