Neural and hormonal mechanisms in aggression

Question 1

What neural mechanisms are involved in aggression?

Answer 1

• The limbic system
• orbitofrontal cortex and serotonin

Question 1

What is the limbic system?

Answer 1

• is a collection of subcortical structures in the brain involved in regulating emotional behaviour including aggression

Question 2

What did Papez and Maclean define the the limbic system as?

Answer 2

• as the hypothalamus, amygdala and parts of the hippocampus

Question 3

The reactivity of the amygdala is….

Answer 3

• an important predictor of aggressive behaviour
  (more responsive the amygdala, the more aggressive a person is)

Question 4

What is serotonin?

Answer 4

• A neurotransmitter that has widespread inhibitory effects in the brain
• has a key role in aggressive behaviour

Question 5

What was Gospic et al research study on the reactivity of amygdala?

Answer 5

• participants were subjected to mild provocation
• when they reacted aggressively fMRI scans showed a fast & heightened response by the amygdala
• 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

Question 6

According to Denson et al (2012) what are normal levels of serotonin in the orbitofrontal cortex linked with?

Answer 6

• reduced firing of neurons
• which in turn is associated with greater behavioural self control

Question 7

According to Denson et al (2012) what are decreased levels of serotonin linked with?

Answer 7

• reduction of self -control
• leading to an increase in impulsive behaviour including aggression

Question 8

What did Virkkunen et al compare?

Answer 8

• 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

Question 9

What is a limitation of the limbic explanation?

Answer 9

• recent research shows that non-limbic brain structures are also involved in aggression
• OFC is not part of limbic system but 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

Question 10

What hormonal mechanisms are involved in aggression?

Answer 10

• testosterone
• progesterone

Question 11

What is a strength of the serotonin explanation?

Answer 11

• 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

Question 12

What is testosterone?

Answer 12

• a hormone from the androgen group that is produced mainly in the male testes and is associated with aggressiveness

Question 13

What have people observed about men?

Answer 13

• 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

Question 14

Outline Giammanco et al (2005) study and findings on testosterone

Answer 14

• 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

Question 15

Outline Dolan et al (2001) study and findings on testosterone

Answer 15

• study of violent offenders
• Dolan et al > positive correlation between testosterone levels & aggressive behaviour in offenders in UK maximum security hospitals
• men mostly had personality disorders and histories of impulsively violent behaviour

Question 16

What does evidence say about the hormone progesterone?

Answer 16

• that the hormone progesterone (female ovarian hormone) plays an important role in aggression in women

Question 17

What did Ziomkiewicz et al (2012) find about progesterone?

Answer 17

• found a negative correlation between progesterone levels and self-reported aggression
• suggests that low levels of progesterone are linked to increased aggression in women

Question 18

What is research support is there for the hormonal explanation?

Answer 18

• 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

Question 19

What is a limitation of hormonal explanations?

Answer 19

• mixed evidence of the link between testosterone & aggression in humans
• Carre & Mehta 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