3.1 Aggression

Question 1

What is aggression?

Answer 1

An act that is intended to harm another individual physically or psychologically

Question 1

What is the limbic system?

Answer 1

Subcortical structures in the brain thought to be closely involved in regulating emotional behaviour e.g aggression

Question 2

Name 3 components of the limbic system

Answer 2

• Hypothalamus
• Amygdala
• Parts of the hippocampus

Question 3

What is the link between the amygdala and aggression?

Answer 3

The reactivity of the amygdala in humans and mammals is a predictor of aggressive behaviour. The more responsive the amygdala, the more aggressive a person is

Question 4

Describe Gospic et al (2011) study on the role of the amygdala

Answer 4

• Participants subjected to mild provocation
• When participants acted aggressively fMRI scans showed fast and heightened response by amygdala
• A benzodiazepine drug, which reduces arousal of ANS taken before provocation
• Led to a decreased activity of the amygdala

Question 5

What are the neural mechanisms in aggression?

Answer 5

• The limbic system (hypothalamus, amygdala, hippocampus)
• Orbitofrontal cortex and serotonin

Question 6

What is serotonin?

Answer 6

A neurotransmitter that has widespread inhibitory effects in the brain

Question 7

Describe the link between serotonin and aggression?

Answer 7

• Normal serotonin levels linked with reduced firing of neurons which is associated with greater behavioural self control
• Serotonin deficiency in the Orbitofrontal cortex, disrupts the mechanism and leads to impulsiveness (linked with aggression)

Question 8

What is testosterone?

Answer 8

A hormone from the androgen group that is produced mainly in the male testes (associated with aggressiveness)

Question 9

What is the link between testosterone and aggression?

Answer 9

Testosterone has a role in regulating social behaviour via its influence on certain areas of the brain implicated in aggression

Question 10

What did Giammanco et al (2005) find about the role of testosterone?

Answer 10

• Through castration studies on animals, showed that removing the testes reduces the aggression in the males of many species
• Giving injections of testosterone to the same animals restores aggressive bahviour

Question 11

What did Dolan et al (2001) find about the role of testosterone in aggression?

Answer 11

Found a positive correlation between testosterone levels and aggressive behaviours in a sample of 60 violent offenders

Question 12

What did Ziomkiewicz et al (2012) find about the role of progesterone in aggression?

Answer 12

Found a negative correlation between progesterone levels and self-reported aggression (suggests low progesterone levels linked to increased aggression in women)

Question 13

When are progesterone levels lowest (leading to increased aggression)

Answer 13

Levels of progesterone are lowest during and just after menstruation

Question 14

What are the hormonal mechanisms in aggression?

Answer 14

• Testosterone
• Progesterone

Question 15

AO3 of neural mechanisms in aggression

Answer 15

1. Other brain structures:
- recent evidence shows non-limbic structures also involved
- limbic structures function with the orbitofrontal cortex which is not part of the limbic system
- OFC involved in impulse regulation + inhibition of aggressive behaviour
- Coccaro: OFC activity reduced in psychiatric disorders that feature aggression
- this reduction causes aggression
- shows neural regulation of aggression more complex

2. Drugs and serotonin:
- drugs e.g paroxetine that increase serotonin also found to reduce levels of aggressive behaviour
- Berman et al: gave participants placebo or dose of paroxetine
- then engaged in lab-based game involving giving + receiving electric shocks in response to provocation
- paroxetine group consistently gave fewer and less intense shocks than placebo
- evidence of casual link between serotonin and aggression

Question 16

One strength and one limitation for hormonal mechanisms in aggression

Answer 16

1. Animal research: -
- Giammanco et al’s animal study reviews confirms the role of testosterone
- in male rhesus macaque monkeys = increased testosterone levels and aggressive behaviour during mating season
- in rats, castration of males reduces testosterone and also mouse killing behaviour
- injecting female rats with testosterone increases mouse killing

2. Dual-hormone hypothesis:
- Carre and Mehta: developed a dual hormone hypothesis
- claims that high levels of testosterone lead to aggression but only when cortisol levels are low (responds to chronic stress
- when cortisol is high testosterones influence on aggression is blocked
- combined activity of testosterone and cortisol may be better predictor of aggression

Question 17

What are the 4 genetic factors in aggression?

Answer 17

• Twin studies
• Adoption studies
• The MAOA gene
• Gene-environment interactions

Question 18

What Is the MAOA gene?

Answer 18

A gene which controls the production + activity of the MAO-A enzyme (regulates serotonin) in the brain

Question 19

Describe Coccaro et al’s (1997) twin studies into aggression

Answer 19

• Studied men who were either monozygotic or dizygotic twins
• For aggressive behaviour defined as direct physical assault, researchers found concordance rates of 50% for MZ twins and 19% DZ twins
• The corresponding figures for verbal aggression were 28% MZ and 7% DZ

Question 20

Why would there be a difference in aggression between monozygotic and dizygotic twins?

Answer 20

• Monozygotic twins share 100% of their genes but dizygotic only share around 50%
• It would be expected to find greater similarities in aggression between MZ twins if aggression influenced by genetic factors
• This is because both MZ and DZ twins raised together in the same environment, but MZ twins have greater genetic similarity

Question 21

Why are adoption studies useful for aggression?

Answer 21

Similarities in aggressive behaviour between an adopted child and their adoptive parents suggest environmental influences are operating

Question 22

Describe Rhee and Waldman (2002) adoption studies on aggression

Answer 22

• Carried out meta-analysis of adoption studies of direct aggression and antisocial behaviour
• Found that genetic influences accounted for 41% the variance in aggression

Question 23

What is the role of the MAO-A enzyme?

Answer 23

Regulates the neurotransmitter serotonin

Question 24

What is the link between the MAOA gene and aggression?

Answer 24

- The gene comes in different variants. The low activity variant (MAOA-L) results in low activity of the MAO-A enzyme (deficiency) - This MAOA-L variant has been linked to high levels of aggressive behaviour

Question 25

What did Lea and Chamers (2007) find on the influence of the MAOA gene in aggression

Answer 25

Found research showed MAOA-L variant possessed by 56% of New Zeland Maori men (compared to 34% caucasians)

Question 26

What did Brunner et al (1993) find about the link between MAOA-L and aggression?

Answer 26

- Studied 28 men from large Dutch family who were repeatedly involved in impulsively aggressive/violent criminal behaviors e.g rape, attempted murder - The men had abnormally low levels of the MAO-A enzyme and MAOA-L gene variant

Question 27

What does gene-environment interactions suggest?

Answer 27

Suggests that genes do not function in isolation. MAOA-L gene activity only related to adult aggression when combined with early traumatic life experiences

Question 28

Describe Frazzetto et al's (2007) study into gene-environment interactions

Answer 28

- Found association between higher levels of antisocial aggression and the MAOA-L variant in men - This only the case in those who had experienced significant trauma e.g sexual/physical abuse during first 15 years of life - Those who had not experienced childhood trauma did not have particularly high levels of aggression as adults (even if possessing MAOA-L)

Question 29

AO3 for genetic factors in aggression

Answer 29

1. Research support - MAOA- L gene associated with greater aggression - Mertins et al: converse is also true, men with high + low variants of gene took part in money distributing game - Men with MAOA-H gene made fewer aggressive moves than MAOA-L 2. Complex link - MAOA-serotonin-aggression link is unclear - MAOA-L gene should lead to higher serotonin (MAOA-L does not deactivate serotonin, leaving more for synaptic transmission) - more accurate to say serotonin levels are disrupted (rather than higher/lower) 3. Problem with twin studies - Lack validity due to **equal environment assumption** - DZ twins may not share their environment to the same extent as MZ twins - MZ twins treated similarly especially by parents - Concordance rates are inflated + genetic influences not as great