Biological Explanation of Aggression: Neural and Hormonal

• What is agression?

  Any physical or non-physical behaviour that is threatening or intends to harm humans or objects.
• What is the hypothalamus involved in?

  • Activating the sympathetic nervous system.
  • Controlling the fight or flight response.
  • Producing aggression
• What is the amygdala involved in?

  • determines the emotional meaning of events in the environment.
  • decides whether an event is ‘good’ or ‘bad’.
• If the events are bad or dangerous, then the amygdala sends nerve impulses

  to the hypothalamus, causing it to produce aggressive behaviour.
• The main part of the brain involved in storing long-term memories is the hippocampus.
• What role does the hippocampus play in aggression?

  It sends information stored in our memory to the amygdala.
• Together, the hippocampus, amygdala and hypothalamus are called…

  The limbic system
• The frontal cortex sends electrical signals that inhibit neurons in the amygdala. This causes neurons in the amygdala to generate fewer nerve impulses.
• If a person’s frontal cortex can’t generate electrical signals then...

  • their amygdala will not be inhibited.
  • signals will continue to be sent to the hypothalamus.
  • they are more likely to be aggressive.
• A = Frontal cortex

  B = Hippocampus

  C =

  D = Limbic system

  E = Hypothalamus

  F = Amygdala

  
• What role does the frontal cortex play in aggression?

  It inhibits neurons in the amygdala.
• If the frontal cortex is damaged, then…

  • the brain continues to produce aggressive behaviour.
  • the amygdala keeps sending impulses to the hypothalamus.
• The hypothalamus produces aggression.

  The amygdala decides whether an event in the environment is good or bad.

  The hippocampus accesses memories to decide whether an event is threatening.

  The frontal cortex stops aggression.
• When neurons send electrical signals to other neurons at the synapse, they release neurotransmitters that bind to receptors on the post-synaptic membrane.
• Serotonin plays a role in controlling our mood and determining how we feel about things.
• When negative electrical charge flows into neurons the neurons are inhibited and are less likely to generate nerve impulses.
• Since serotonin inhibits neurons in the amygdala, this means that the amygdala sends fewer nerve impulses to the hypothalamus.
• Serotonin in aggression

  • Serotonin inhibits neurons in the amygdala.
  • Serotonin reduces aggressive behaviour.
  • Serotonin reduces nerve impulses sent to the hypothalamus.
• What are hormones?

  Chemical messengers that are released into the bloodstream.
• Because men produce more testosterone than women they are more likely to display aggression than women.
• What is testosterone?

  • Testosterone is produced and released by the adrenal glands and the sex glands.
  • Testosterone is a hormone that increases our tendency to be aggressive.
• What is the name of the part of the brain that is involved in controlling the fight or flight response as well as producing aggressive behaviour?

  hypothalamus
• The amygdala determines the emotional meaning of events in the environment, which means deciding whether events are positive or negative.
• What is the name given to the hippocampus, amygdala and hypothalamus?

  The Limbic system
• The part of the brain that determines the emotional meaning of an event.

  Amygdala
• The main part of the brain involved in storing long-term memories.

  Hippocampus
• Sends electrical signals to inhibit neurons in the amygdala.

  Frontal Cortex
• Sends information stored in our memory to the amygdala.

  Hippocampus
• If the frontal cortex is damaged, what effect will this have on aggression?

  It will increase aggression.
• The neurotransmitter that is involved in aggression is called serotonin. The neurotransmitter ....

  • reduces nerve impulses sent to the hypothalamus
  • inhibits neurons in the amygdala
  • reduces the likelihood of aggressive behaviour.
• The hormone that is involved in aggression is called testosterone. This hormone is...

  • a chemical messenger released into the bloodstream
  • is released by the testes
  • is released by the adrenal glands
  • increases our tendency to be aggressive.
• Name the three brain regions that we’ve seen are involved in producing aggression.

  Amygdala, hypothalamus and the frontal lobe
• Support for the role of the amygdala in aggression

  Sumer et al

  • They conducted a case study looking at a 14 year old girl with excessive aggression.
  • An MRI scan revealed that she had a tumour pressing onto her amygdala
• Support for the role of the amygdala in aggression.

  Mpakopoulou's study

  • Before the amygdalotomy, the patients had excessive activity in their amygdala.
  • Before the surgery, the patients were displaying high levels of aggression.
  • The amygdalotomies reduced aggression in the patients by 33-100%.
• If neurons in the amygdala are damaged, so that there is less neural activity in the amygdala, then there should be less nerve impulses sent to the hypothalamus, meaning that aggression should decrease.
• One limitation of the study support for the role of the amygdala in aggression is that…

  • the results of the studies haven’t all been consistent.
• Serotonin is released at synapses in the limbic system, where it inhibits neural activity, leading to a decrease in aggression.
• Crocketts investigation into the role of serotonin in controlling aggression

  • Crockett used a social decision-making game to investigate the role of serotonin in aggression.
  • Crockett found that participants with increased serotonin behaved less aggressively.
• Support for the role of Testosterone in Aggression

  • Dabbs et al. conducted a correlational study looking at the relationship between testosterone and violence in criminals
  • Further support for the role of testosterone in aggression comes from studies showing that men display more aggression than women.
• Limitations of support for the Role of Testosterone

  • The studies are correlational - therefore can't establish a cause-and-effect relationship.
  • Not always consistent - not replicated everytime