AGGRESSION

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…