Neural and Hormonal Mechanisms in Aggression

P: there's good research into the effect of drugs
E: drugs (e.g. paroxetine) which increase serotonin have been found to reduce levels in aggressive behaviour. Berman et al. (2009) gave ppts either a placebo or a dose of paroxetine. ppts then took part in lab-based game involving giving & receiving electric shocks in response to provocation (i.e. insults). Paroxetine group consistently gave fewer & less intense shocks than the placebo group
E: strength - study is evidence pf a casual link between serotonin function and aggression.

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Papez (1937) & Maclean (1952) linked limbic system to emotional behaviours, including aggression

defined limbic system as the hypothalamus, amygdala and parts of the hippocampus (plus other structures)

Aggression - feelings of anger or antipathy resulting in hostile or violent behaviour; readiness to attack or confront

proactive aggression = cold-blooded aggression - planned method of getting what you want

reactive aggression = hot-blooded aggression - angry, impulsive & accompanied by physiological arousal

reactivity of the amygdala in humans and other mammals is an important predictor of aggressive behaviours (i.e. the more responsive the amygdala, the more aggressive a person is)

used lab method to assess aggressive behaviour called the Ultimatum Game* involving two players ;proposer and responder

proposer offers to split money in certain way with responder. if responder accepts, the money is split as proposed. if responder rejects offer both receive nothing.

when ppts reacted aggressively to mil provocation, fMRI scans showed a fast & heightened response by the amygdala

a benzodiazepine drug (which reduces arousal of the Autonomic nervous system) taken before provocation led to two effects: it decreased the activity of the amygdala & halved number of rejections (i.e. reduced aggression), illustrating again the role of the amygdala

serotonin = neurotransmitter which has widespread inhibitory effects in brain, i.e. it slows down & calms neuronal activity

normal levels or serotonin in the orbitofrontal cortex (OFC) (area just behind eye-socket in frontal cortex) are linked with reduced firing of neurones which in turn is associated with greater behavioural self-control.

decreased serotonin (deficiency) disrupts this mechanism, reducing self-control and leading to an increase in impulsive behaviour including aggression (Denson et al.)

Virkkunen et al. (1994) compared levels of serotonin breakdown product (a metabolite called 5-HIAA) in the cerebrospinal fluid of violent impulsive and violent non-impulsive offenders

P: more recent research shows non-limbic brain structures are also involved in aggression
E: limbic structures function together with OFC which isn't part of limbic system. OFC is involved in impulse regulation & inhibition of aggressive behaviour. Caccaro et al. (2007) suggests OFC activity is reduced in psychiatric disorders featuring aggression. reduced activity disrupts OFC's impulse-control function, in turn causing aggressive behaviour
E: limitation - shows neural regulation of aggression is more complex than theories focusing on the amygdala suggests.

P: there's good research into the effect of drugs
E: drugs (e.g. paroxetine) which increase serotonin have been found to reduce levels in aggressive behaviour. Berman et al. (2009) gave ppts either a placebo or a dose of paroxetine. ppts then took part in lab-based game involving giving & receiving electric shocks in response to provocation (i.e. insults). Paroxetine group consistently gave fewer & less intense shocks than the placebo group
E: strength - study is evidence pf a casual link between serotonin function and aggression.

Testosterone

testosterone = androgen responsible for development of masculine features & thought to be linked to aggressive behaviour for several reasons

many people have seen men are generally more aggressive than women. men become more aggressive towards other men at time in development when testosterone are highest (after age 20)

testosterone have role in regulating social behaviour via its influence on certain areas of the brain implicated in aggression

castration studies of animals shows removing testes (the source of testosterone) reduces aggression in males in many species.

giving injections of testosterone to same animals restores aggressive behaviours.

some evidence for similar association in humans comes from studies of prison populations, e.g. violent offenders

Dolan et al. (2001) found positive correlation between testosterone levels and aggressive behaviours in a sample of 60 offenders (men) in the UK maximum security hospitals. these men mostly had personality disorders (such as psychopathy) and histories of impulsively violent behaviours

some evidence that progesterone (a female ovarian hormone) plays an important role in aggression of women

levels of progesterone vary during ovulation cycle & are lowest during & just after menstruation.

Ziomkiewicz et al. (2012) found a negative correlation between progesterone levels and self-reported aggression. this suggests that low levels of progesterone are linked to increased aggression in women