Neural and hormonal mechanisms in aggression Flashcards
What neural mechanisms are involved in aggression?
- The limbic system
- orbitofrontal cortex and serotonin
What is the limbic system?
- is a collection of subcortical structures in the brain involved in regulating emotional behaviour including aggression
What did Papez and Maclean define the the limbic system as?
- as the hypothalamus, amygdala and parts of the hippocampus
The reactivity of the amygdala is….
- an important predictor of aggressive behaviour
(more responsive the amygdala, the more aggressive a person is) - key role in how mammals assess & respond to environmental threats
Whose study is the amygdala activity illustrated in?
Gospic et al (2001)
What was Gospic et al research procedure
- participants were subjected to mild provocation
- when they reacted aggressively fMRI scans showed a fast & heightened response by the amygdala
What was Gospic et al research findings?
- When a benzodiazepine drug (reduces arousal in the ANS) was taken before provocation this led to two effects :
- decreased the activity of the amygdala
- halved the number of aggressive behaviours
- illustrating the role of the amygdala
What is serotonin?
- A neurotransmitter that has widespread inhibitory effects in the brain
- has a key role in aggressive behaviour
According to Denson et al (2012) what are normal levels of serotonin in the orbitofrontal cortex linked with?
- reduced firing of neurons
- which in turn is associated with greater behavioural self control
According to Denson et al (2012) what are decreased levels of serotonin linked with?
- reduction of self -control
- leading to an increase in impulsive behaviour including aggression
What did Virkkunen et al compare?
- compared levels of a serotonin breakdown product in the spinal fluid of violent-impulsive and violent non impulsive offenders
- found that the levels were significantly lower in the impulsive offenders
- suggests low serotonin increases aggressive behaviours
What is a limitation of the limbic explanation?
- recent research shows that non-limbic brain structures are also involved in aggression
- OFC is not part of limbic system nut functions together with the amgydala
- OFC is involved in impulse regulation & inhibition of aggressive behaviour
- According to Coccaro et al> OFC activity is reduced in psychiatric disorders that feature aggression as reduced activity disrupts the OFC’s impulse-control function> causing aggression
- over reliance on the limbic system as an explanation
What is a strength of the serotonin explanation?
- research into the effects of drugs
- Drugs that increase serotonin have been found to also reduce levels of aggressive behaviour
- Berman et al > found that p’s who were given paroxetine behaved less aggressively when provoked while playing a video game (delivered fewer & intense shocks) than a control group
- Evidence of a causal link between serotonin & aggressive behaviour
What hormonal mechanisms are involved in aggression?
- testosterone
- progesterone
What is testosterone?
- a hormone from the androgen group that is produced mainly in the male testes and is associated with aggressiveness
What have people observed about men?
- that men are generally more aggressive than women
- Daly & Wilson> men become more aggressive towards other males during time of development (after age 20) when testosterone levels are the highest
- testosterone has a role of regulation social behaviour
Outline Giammanco et al (2005) study and findings on testosterone
- found castration studies of animals show that removing testes reduces aggression in males of many species
- also giving injections of testosterone to the same animals restores aggressive behaviour
- shows cause & effect between levels of testosterone & aggressive behaviour
Outline Dolan et al (2001) study and findings on testosterone
- study of violent offenders
- Dolan et al >positive correlation between testosterone levels & aggressive behaviour in 60 offenders in UK maximum security hospitals
- men mostly had personality disorders and histories of impulsively violent behaviour
What does evidence say about the hormone progesterone?
- that the hormone progesterone (female ovarian hormone) plays an important role in aggression in women
What did Ziomkiewicz et al (2012) find about progesterone?
- found a negative correlation between progesterone levels and self-reported aggression
- suggests that low levels of progesterone are linked to increased aggression in women
What is research support is there for the hormonal explanation?
- research with animals
- Giammanco et al > meta-analysis-reviewed studies which confirmed the role of testosterone
- e.g. in male Rhesus macaque monkeys> there is increase in T levels & aggressive behaviour during mating season
- in rats, castration of males reduces T & also mouse killing behaviour
- injecting female rats with T also increased mouse-killing
- Shows the role of testosterone
What is a limitation of hormonal explanations?
- mixed evidence of the link between testosterone & aggression in humans
- Carre & Mehta (2011) developed a dual hormone hypothesis to explain why
- hormone cortisol plays a central role in body’s response to chronic stress
- claim that ^ levels of T lead to aggressive behaviour only when levels of cortisol are low
- when cortisol levels are ^, T influence on aggression = blocked
- incomplete explanation, both hormones may be a better predictor of aggression than each alone
What does Cocarro et al add to the limitation of the limbic explanation?
- Coccaro et al > OFC activity is reduced in those with psychiatric disorders that feature aggression
- reduced activity disrupts OFC impulse control function = aggressive behaviour
= limited explanation & more complex than theories focusing on amygdala suggest
