PSY352H5 Lecture Notes - Lecture 8: Neurochemistry, Amygdala, Leafy Seadragon
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Lecture 8: Aggression
Outline
• Introduction
• Aggression and the brain
• Neurochemistry and aggression
• Situational aggression
• Alcohol and aggression
• Paper discussion
Introduction
• Aggression – violent or aggressive attitude toward another
• There is physical and non-physical
• Red deer engage in non-physical aggression where they would walk in a circle and size the
opponent up before deciding whether they would want to get physical or not
Aggression and the brain
Reward centres
• Revenge is sweet
• Greater activation in the Nacc and VLPFC associated with retaliation aggression
Taylor aggression paradigm
• Opponents come to the study and are told if they lose the task then the opponent will play a loud
sound that the opponent will pick
• High provocation: a high want for revenge
o Were more likely to pick a louder noise for the opponent
• Low provocation: told that they lost and only got a low noise
Amygdala
• Small amygdala correlated with high levels of aggression
Neurochemistry and aggression
Hormones
• Testosterone – steroid hormone produced in gonads and regulated by the hypothalamus and
pituitary gland
o But also creates low sociality
• Associated with high levels of aggression, particularly in males
• Influenced by social interactions
o Challenge hypothesis: male vs. male interactions cause increase in testosterone
o Winner effect: experience winning in a situation makes it more likely to win another
aggressive situation due to the raise of testosterone levels
o Winner-challenge effect: Winning in an aggressive situation increases testosterone,
increases aggression, which increase the likelihood of winning future interactions
▪ Number of times they won an interaction, 0, 1, 2, 3, or no interaction
▪ Placed into a box, developed their territory, sedated male was placed into nest
▪ Testing phase, unfamilar larger put into cage and measured number of attacks
and latency to attack then measured blood testosterone
▪ Only significant difference between those who had never had an encounter; those
with 1, 2 and 3 winning encounters all attacked more and has higher blood
testosterone compared to controls.
Challenge vs. winner hypothesis
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• Male-male interactions increase testosterone levels, which then sustains aggressive behavior
• Captive males have lower spikes in testosterone compared to wild males
Winner – challenge effect
• Winning in an aggressive situation increases testosterone, increases aggression, which increase
the likelihood of winning future interactions
• Number of times they won an interaction, 0, 1, 2, 3, or no interaction
• Placed into a box, developed their territory, sedated male was placed into nest
• Testing phase, unfamilar larger put into cage and measured number of attacks and latency to
attack then measured blood testosterone
• Only significant difference between those who had never had an encounter; those with 1, 2 and 3
winning encounters all attacked more and has higher blood testosterone compared to controls
Hormones in insects
• Insects don’t have testosterone but they have juvenile growth hormone
• Juvenile hormone
• Similar cost benefits as testosterone
Aggression and hormones in humans?
• Both groups had increased testosterone levels when they saw their team winning even if they
weren’t playing
• But it is possible that watching their own team may also increase testosterone just due to seeing
their team as may cause pride
Neurotransmitters
Neurotransmitters – Serotonin
• Related to lower aggression
• Related to stress and aggression (discussed later)
• Usually inhibitory effect on aggression
o 5-HT agonism results in reduced aggression
o 5-HT knockout leads to increased aggression
Neurotransmitters – Dopamine
• related to the rewarding aspects of motivation
• looked at a study with rats with an insertion of a male that could be seen as a competition
o caused increased levels of dopamine when the mouse entered
• Competitive motivation
• Also related to risk taking behaviour
• Dopamine antagonists used to treat aggressive behaviour in humans
Neurotransmitters - GABA
• Increase or decrease aggression, depending on administration
• Benzodiazepines prescribed to reduce aggressive behaviour, however, violent outbursts are
common
• Alcohol (GABA modulator) found increases in aggression in certain conditions (discussed more
later)
Situational aggression
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