Aggression: Neural and Hormonal Mechanisms (Outline)

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Neural Influences

1) The Limbic System 

    - The Amygdala

    - The Hippocampus

2) Seratonin

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Hormonal Influences

1) Testosterone

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Neural Influences - The Limbic System

Made up of several subcortial structures - amydala most closely associated with aggression. Subcortial structures thought to be closely involved in regulating emotional behaviour eg aggression

Amydala - Evaluates emotional importance of sensory info, prompts appropriate response. If malfunctions, eg due to tumour, damage or atypical development, levels of T can be raised - increases aggression levels.

Hippocampus - Formation of LT memories - comparisons can be made between current threats and past experiences. Impaired hippocampal function stops nervous system from putting things into context. May can amygdala to respond inappropriately to sensory stimuli

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The role of serotonin

A neurotransmitter thought to regulate feelings of well-being.

Lowering serotonin levels linked with depressing mood and increasing aggression - side effects of prescription drugs eg Prozac that lower serotonin levels.

Exact role in aggression unclear. Currently, thought to mediate individual's response to situation. Activation in brain's limbic region (centre of emotional response) not as controlled as much by frontal cortex in those w/ low serotonin levels.

Those with low serotonin has less control over emotional response, can lead to aggression - Crockett + Passamonti (2011)

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Sensory Deficiency Hypothesis

Seratonin influences aggressive and violent behaviour, plus overeating, depression, alcoholism and violent suicide.

Normal levels - calming eggect on neural firing in brain. S inhibits firing of amygdala

Low levels - aggression, risk taking - less able to control impulsive and aggressive behaviour

Tryptophan an amino acid that produces S. Found in chocolate, meat and cheese. High levels = high levels of S = decrease aggression

Dexfenfluramine drug - alters S levels, increases aggressive behaviour

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Testosterone

Male sex hormone - influence aggression from adolescence. Responsible for changes that occur during puberty.

Found in both sexes, adult males produce 10x more than adult females. Highest level in males 15-25 years - most likely group to commit violent crimes.

Reducing T levels by castration often used to reduce aggression in pet, farm and zoo animals. Throughout history, servants/slaves castrated to make them sager to royal court.

If individual has high levels of T, activity in orbito-frontal cortex reduced - in an emotional situation, could be heightened emotionally aggressive response.

T influences activity of seratonin in brain - can reduce serotonergenic activity. Low levels of this implicated in increased aggressive behaviour. Appears T doesn't just have effect in isolation, but mediayes the effects of other biochemicals too

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