Brain and Hormones in Aggression

How does the brain cause aggression?
Brain: The limbic system and the amygdala are both parts of the brain that may affect aggression.

The limbic system: A set of brain structures that lie in the middle of the brain, it is responsible for emotions needed for survival, like fear and aggression.

The amygdala: A structure in the brain that recognises emotion, problems with the amygdala may cause aggression Some human case studies do offer some evidence that the amygdala might cause aggression.

Evidence
King (1961): Describes a case of a woman whose amygdala was electrically stimulated during an operation, she became threatening and verbally aggressive until the electrical current was turned off.

Charles Whitman: In 1966 he killed 13 people, left behind a note asking doctors to examine his brain and they found out that he had a brain tumour pressing against his amygdala

It is difficult to research the human brain biology because it is unethical to manipulate the human brain, meaning that we must use animals brains, which are similar but not similar enough for us to make a direct comparison. Animals are very different from humans. Limited direct proof.

How do Hormones cause aggression?
Testosterone is a male sex hormone that causes aggression, both men and women have it but usually men have more.

Aggression in animals:

Injecting animals with testosterone or removing the testes leads to increased or decreased levels of aggression. Castrating a male animal lowers its testosterone levels, making the animal less aggressive. But if the same animal is then injected with testosterone its aggression is restored to a level similar to that before the castration

Aggression in humans:

Taking blood samples to humans, measuring testosterone levels and comparing this to their aggressiveness. Some correlation studies have found a relationship between high testosterone levels and questionnaire results showing greater reported aggression

Evaluating the role of testosterone on aggression
Strengths: Weaknesses:
 * In animals there is a clear cause and effect relationship between testosterone and aggression
 * Human studies show a relationship between aggression and testosterone in correlation studies
 * Not all humans with high testosterone levels are aggressive
 * Correlation and animal studies may not apply to humans, only shows correlation not real link
 * This explanation of aggression completely ignores the high impact of upbringing and social circumstances on our behaviour

Evaluating the link between brain and aggression
Strengths: Weaknesses:   
 * Animals studies that have involved damage to or removal of the amygdala offer evidence for its link with aggression
 * The case study of Charles Whitman and the case described by King are all evidence for its link with aggression in humans
 * Studying the human brain is difficult and can be very risky, no way to make sure areas of the brain are linked to aggressions
 * Animals and humans are different in many ways, so animal research may not be applicable to humans
 * Aggression could equally be explained by the way children copy the media