Neural and hormonal mechanisms in aggression

Question 1

What are the neural mechansims in aggression ?

Answer 1

• The limbic system
• Orbitofrontal cortex and serotonin

Question 2

What is the limbic system?

Answer 2

• The limbic system = subcortical structures in the brain, including the hypothalamus and amygdala thought to be closely related in regulating emotional behaviour, including aggression
• Papez and Mclean linked the limbic system to aggression

Question 3

How is the amygdala linked to aggression?

Answer 3

• The reactivity of the amygdala in humans and other mammals is an important predictor of aggressive behaviour
• For example, the more responsive the amygdala is, the more aggressive the person is
• This means the amygdala has a key role in how mammals assess and respond to environmental threats

Question 4

What is research on the amygdala?

Answer 4

• The amydalas activity has been investigated by Gospic et al (2011)
• Some participants were subjected to mild provocation. When participants reacted aggressively, FMRI scans showed a fast and heightened response of the amygdala
• Participants were subjected to aggression by being given an ultamatim game where participants were asked to split or keep money with a confederate
• If they agreed to split, the money was split in half
• However if the participant agreed to split and the confederate refused, the participant left with nothing
• More activity in the amydala occurred when unfair desicions were made

Question 5

What else did Gospic et al research

Answer 5

• Gospic et al also gave participants a benzodiazepine drug which reduced activity of the ANS
• this lead to decreased activity of the amygdala and halved the number of money offer rejections
• This shows the role of the amygdala

Question 6

What is the role of serotonin and the orbitofrontal cortex

Answer 6

• serotonin is a neurotransmitter that has widespread inhibitory effects in the brain as it slows down and calms neuronal activity
• Denson et al (2012) = Normal levels of serotonin in the orbitofrontal cortex are linked with reduced firing of neurons, which in turn is associtaed with greater behavioural self control. Decreased serotonin distrupts this mechanism, reducing self control and leading to an increase in impulsive behaviour including aggression
• Virkkunen et al compared levels of serotonin breakdown products in the cerebrospinal fluid of violent impulsive and violent non - impulsive offenders. The levels were significantly lower in impulsive offenders.

Question 7

What is a strength of the role of serotonin

Answer 7

• One strength of serotonin explanation is research into the effects of drug. Drugs that increase serotonin (such as paroxetine) have been found to also reduce levels of aggressive behaviour. Berman gave participants either a placebo or a dose of paroxetine. The participants the took place in a lab - based game that involved giving and recieving electrical shocks in response to provocation. The paroxetine group consistently gave fewer and less intense shocks than the placebo group. This shows a causal link between serotonin and aggression

Question 8

What is a limitation to the role of serotonin

Answer 8

• One limitation of the limbic explanation is that there is recent research that says that non - limbic brain structures are also involved in aggression. Limbic structures such as the amygadla works together with the OFC (not in the limbic system) which is associated with impulse regulation and inhibition of aggressive behaviour. According to Emil Coccaro, Ofc activity is reduced in those psychiatric disorders that feature aggression

Question 9

Explain the link of testosterone to aggression

Answer 9

• The male sex hormone is an androgen responsible for the development of masculine features.
• Men become more aggressive toward other men at a time in development, after the age of 20 when testosterone levels are highest. testosterone has a role in regulating social behaviour via its influence on certain areas of the brain implicated in aggression.
• Castration studies of animals show that removing the testes reduces aggression in the males of many species. Giving injections of testosterone to the same animals restores aggresive behaviour. (Gimmanco et al)
  Dolan et al found a positive correlaton between testosterone levels and aggressive behaviours in a sample of 60 offenders in UK maximum secuirty hospitals. these men had mostly personality disorders such as psychopathy and histories of impusively violent behaviour

Question 10

Explain the link of progesterone to aggression

Answer 10

• there is evidence that progesterone plays an important role in aggression in women. Levels of progesterone vary during ovulation cycles and are lowest during and just after menstruation. Anna Zimokiewicz et al found a negative correlation between progesterone levels and self reported aggression. This shows that low levels of progesterone are linked to increased aggression in women

Question 11

What is one strength of hormonal mechanisms of aggression?

Answer 11

• One strength is that there is research support from non - human animals. Marco Gimmonco et als reviews of studies confirm the role of testosterone. For example, male macaque monkeys show that there is an increase in both testosterone levels and agggressive behaviour during mating season. In rats, castration of males reduces testosterone and also mouse-killing, Injecting female rats with testosterone increases mouse - killing. This shows a role of testosterone with aggression in a range of animal species

Question 12

What is a limitation of the role of testosterone

Answer 12

• One limitation is that there is mixed evidence between testosterone and levels of aggression. Carre and Mehta developed a dual hormone hypothesis to explain why. they claim that high levels of testosterone links to aggressive behaviour, only when coupled up with low cortisol that are low. when cortisol is high, testosterones influence on aggression is blocked. This shows that the hormone cortisol plays a central role in the bodys response to chronic stress