The Role of Neural and Hormonal Mechanisms in

Aggression

To understand how destroying the amygdala reduces aggression. Explain how testosterone leads to aggressive behaviour.

Is aggression

• Nature or nurture?

Phineas Gage

• One of the best examples of how brain injury can influence aggressive behaviour is the case of Phineas Gage.

• Working on a railway in 1848, he had an accident in which a tamping iron went up through his face , behind his left eye and out through the top of his head.

• He survived the accident, but his personality was changed, including a huge increase in aggression.

*@!* off, I’ve got a splitting

headache!

Neural Mechanisms – Brain structure• Normal aggressive behaviour is not

dependent on separate brain structures, but interaction of a system of structures.

Organised hierarchically and moderated by the pre-frontal cortex.

The Role of the Amygdala

• Kluver-Bucy syndrome – taming effect found in rhesus monkeys by removing part of the temporal lobes and therefore destroying the amygdala.

• Narabyashi et al (1972) – 43 / 51 patients whose amygdala was destroyed through psychosurgery showed reduced aggression afterwards.

• Mark & Ervin (1970) – case study of female patient behaviour following electrical stimulation of amygdala.

• She exhibited facial grimacing, became very angry and flung herself at the wall.

• Ashford (1980) – temporal lobe epileptics often become aggressive, attacking furniture and people.

The Role of Neurotransmitters

• The neurotransmitter serotonin influences aggressive behaviour.

• In research with vervet monkeys, reducing serotonin levels resulted in increased aggressive behaviour, whereas increasing serotonin decreased the aggressive occurrences.

• Drugs to raise serotonin levels, such as trytophan have been given to juvenile delinquents and unpredictable institutionalised patients.

The relationships found here are

CORRELATIONAL. What are the weaknesses of correlational research?

So… the higher the serotonin level, the lower the aggression.

Muller et al (2003) showed 6 male psychopaths and 6 male controls a series of positive and negative pictures whilst in MR scanner. Found increased activity in the amygdala. The exact role of the amygdala in

aggression is unclear, but it is certainly a significant one. Research suggests an interaction between the amygdala and the pre-frontal cortex.

The Role of the Prefrontal Cortex

• Regulates the emotional responses driven by the amygdala.

• Damage to prefrontal cortex results in impulsivity, immaturity and loss of control.

• Anderson et al (1999) – damage during infancy related to aggressive behaviour as adults.

• Case studies comparing early onset damage with adult onset damage to frontal lobes.

• Early onset patients also performed poorly on tests of moral and pro-social reasoning.This brings in a cognitive

element also then. Remember to think

‘approaches’ at all times!

• Raine et al (1997) – investigated brain activity of 41 murderers using PET scans.

• Found reduced glucose metabolism in prefrontal cortex, suggesting this brain area is less active than in normal controls.

• Volkow et al (1995) found violent psychiatric patients had reduced cerebral blood flow to prefrontal cortex.

During the 1940s, frontal lobe lobotomies were performed with startling regularity ; partly because of the ‘calming’ effect on patients with a range of mental health problems – from depression to ADHD to OCD.

GENETIC

• What have animal studies shown about the possibility that aggression is inherited?

• What have concordance studies shown?

• What have adoption studies shown?• Now try the gap fill exercise

Using the cut and stick activity

• Match up the images to the keywords on the display paper and then link them to how they would cause aggression.

NEURAL AND HORMONAL EXPLANATIONS

NEUROTRANSMITTERS• Serotonin – low levels

associated with aggression

• Dopamine – high levels associated with aggression

Antidepressants and antipsychotic drugs reduce levels of aggression (treatment-aetiology fallacy?/cause & effect?)

HORMONES

• Testosterone – link between levels and aggression

Animal researchSex change individuals

Prison populations

BRAIN STRUCTURE

The amygdala is a seat of basic emotions

•Stimulation with electrical impulses provokes rage•Lesioning provokes passivity

The prefrontal cortex is the seat of higher thinking and is linked to the amygdala•Damage causes impulsivity, immaturity – linked to aggression

GROUP DISPLAY

Why might to aggression in groups have been adaptive?

Humans still use group display:

WARFOOTBALL FANSLYNCHINGS

Hormones and Aggression - Testosterone

• Beeman (1947) castrated male mice and found that aggressiveness reduced.

• He later injected the mice with testosterone which re-established their aggressiveness.

• Castration has since been used as a method for making domestic and farm animals more manageable.

• Testosterone is also clearly related to aggression in humans.

• Dabbs et al (1995) – measured testosterone in saliva of 692 adult male prisoners. Found higher levels in rapists and violent offenders than in burglars and thieves.

• Dabbs et al (1996) – looked at 12 fraternities in 2 universities. Members of fraternities with highest levels of testosterone were described as boisterous and macho, those with lowest were attentive and helpful.

But remember these are correlations and what

do we know about correlations?..

• The same effects of testosterone are also found in women.

• Dabbs et al (1988) – female prisoners. Testosterone highest in cases of unprovoked violence but lowest where violence was defensive (eg. In domestic abuse cases)

Other research has found conflicting results, but this is to do with the operationalisation of ‘aggression’.

Think MAID now – (methods, approaches, issues, debates)

Working in pairs, come up with as many points as you can.

• Using the information, create a table of evidence for and against hormones as the cause of human aggression