Neuronal Mechanisms

What is the neural explanation for aggression?

Focus on the role of the brain, nervous system & neurochemistry

What does the neural explanation focus on?

The role of specific brain regions and neurotransmitters such as serotonin

What specific brain regions?

Amygdala, hypothalamus and prefrontal cortex

What is the limbic system?

A group of interconnected brain structures involved in emotion, motivation, memory and autonomic responses

What structures does the limbic system involve?

Amygdala, hypothalamus, hippocampus and cingulate gyrus

Who founded the original idea of the limbic system?

James Papez in the 1930s

What did James Papez propose?

A circuit involved in emotion

Who extended James Papez’s idea?

Paul Maclean, popularising the term ‘limbic system’

What does modern neuroscience propose to be more cautious about?

Saying that the limbic system being a singular ‘emotional centre’

What is emotion now usually understood as?

Arising from distributed neural networks rather than a singular system

What is the role of the amygdala?

Detecting threat, assigning emotional significance to stimuli and generating emotional responses such as fear and anger

What does overactivity or dysfunction in the amygdala cause?

Increased likelihood of hostile/aggressive responses especially when a person perceives threat or provocation

What is the role of the hippocampus?

Formation of long-term memories and in comparing current situations with past experience

Hippocampus’ role in aggression

May help a person judge whether a situation is genuinely threatening by linking present input to memory

Dysfunctional hippocampus

May contribute to misinterpretation of threat which could in turn influence aggressive responding

What is the role of the hypothalamus?

Physiological expression of emotion, including automatic and endocrine responses

Hypothalamus’ role in aggression

Implicated in the initiation and organisation of aggressive behaviour, especially through connections with amygdala and brainstem

What is limbic activity regulated by?

The prefrontal cortex, especially the orbitofrontal cortex and related ventromedial regions

What are the frontal regions involved in?

Decision making, judgement, impulse control and the regulation of emotional responses

What does a normal functioning OFC help provide?

Top-down control over emotional reactions generated in limbic regions such as the amygdalaW

What is reduced/poor OFC activity connectivity associated with?

Impulsivity, poor self-control and a greater risk of reactive aggression

Evidence linking to the Limbic system

Klüver and Bucy (1937), Mark and Ervin (1970), Gospic et al., Lin et al.

Klüver and Bucy (1937) experiment

Surgically removed parts of the temporal lobes in rhesus monkeys, including regions containing the amygdala

What happened after the rhesus monkeys had regions removed? Klüver and Bucy (1937)

The monkey’s became unusually placid, showing reduced fear and they lost their typical aggression and dominant behaviours

What did the rhesus monkey behaviour become known as ?

Klüver and Bucy syndrome

What do the findings of Klüver and Bucy experiment suggest?

The amygdala & surround temporal lobe structures are important for normal emotional & aggressive responding, though the lesions were not limited to the amygdala alone

Mark & Ervin (1970)

Reported case evidence suggesting that electrical stimulation of the amygdala could provoke rage-like or aggressive behaviour

Mark & Ervin (1970) support

Provides support for a casual role of the amygdala in aggressive responding, although the evidence is based on case material rather than large controlled studies

Gospic et al study

Participants played the ultimatum game, in which unfair offers were used as a form of provocation

Gospic et al FRMI

Showed greater amygdala activity when participants rejected unfair offers

Gospic et al- Lorazepam

Both rejections and amygdala activity were reduced

What does the Gospic et al suggest?

The amygdala is involved in retaliatory responses to provocation, through the task measures response to unfairness rather than direct physical aggression