Neural mechanisms in aggression

• Limbic system

  James Papez and Paul Maclean
• Neural mechanisms in aggression


  The limbic system is a structure in the brain that includes the hypothalamus and the amygdala that regulates emotional behaviour, including aggression.
• Amygdala 


  The amygdala is a brain structure which regulates emotional responses. The more responsive the amygdala the more aggressive someone is. So amygdala has a key role in how people assess and respond to different threats.
• Study where amygdala activity is shown is by…


  Katarina Gospic et al
• Gospic et al (2013) used fMRI scans on 48 participants who were asked to play a game with another participant. They found that those who had higher levels of amygdala activation when they saw their opponent’s face also showed greater aggression towards them during the game. This suggests that increased amygdala activity leads to an increase in aggression.
• Gospic et al and the amygdala 


  Participants were subject to mild provocation. When participants reacted aggressively the fMRI scan showed a fast and heightened response by the amygdala. The drug benzodiazepine which reduces the arousal of the autonomic nervous system was given to some participants before the provocation led to decreased activity in the amygdala and it halved the number of rejections leading to reduced aggression.
• Orbitofrontal cortex and serotonin 


  Serotonin regulates self control, high levels increases self control and vice versa.
• Serotonin


  A neurotransmitter with widespread inhibitory effects through the brain. It can slow down and calm neural activity.
• Denson et al- How serotonin works in aggression


  Normal levels of serotonin in the orbitofrontal cortex are linked with reduced firing of neurons which in turn is associated with greater behavioural self control. Decreased serotonin disrupts this mechanism, reducing self control and leading to an increase in impulsive behaviour including aggression.
• Matti Virkkunen et al- impulsive violent behaviour and serotonin

  Virkkunen compared levels of a serotonin breakdown product 5-HIAA in the cerebrospinal fluid of violent impulsive and violent non-impulsive offenders. The levels were significantly lower in the impulsive offenders. So those who had lower levels of serotonin lacked self control there was an increase in impulsive behaviour and aggression.
• What is one limitation of the limbic explanation of aggression?


  There are other non-limbic brain structures involved in aggression.
• How do limbic structures like the amygdala interact with the orbitofrontal cortex (OFC) in relation to aggression?


  The amygdala functions together with the OFC, which is involved in impulsive regulation and inhibition of aggressive behavior.
• What role does the orbitofrontal cortex (OFC) play in aggression?


  The OFC is involved in impulsive regulation and inhibition of aggressive behavior.
• What did Coccardo et al. find regarding OFC activity in psychiatric disorders featuring aggression?


  OFC activity is reduced in those psychiatric disorders that feature aggression.
• What is the consequence of reduced OFC activity according to the study by Coccardo et al.?


  Reduced OFC activity disrupts its impulse-control function, causing aggressive behavior.
• How does the complexity of neural regulation of aggression challenge theories focusing solely on the amygdala?


  The neural regulation of aggression is more complex than theories focusing on the amygdala suggest, as it involves other brain structures like the OFC.
• Emil Coccardo et al 2007


  OFC activity is reduced in psychiatric disorders that feature aggression.
• What is one strength of the serotonin explanation of aggression?


  Research into the effects of drugs
• How do drugs like paroxetine affect aggressive behavior?


  They increase serotonin and reduce levels of aggressive behavior
• What was the design of the study conducted by Mitchell Bergman et al.?


  Participants received either a placebo or a dose of paroxetine
• What type of game did participants take part in during the study?

  A lab-based game involving giving and receiving electric shocks
• What provoked the participants in the lab-based game?


  Insults
• What was the outcome for the paroxetine group compared to the placebo group?


  The paroxetine group gave fewer and less intense shocks
• What does the study by Mitchell Bergman et al. provide evidence for?


  A causal link between serotonin function and aggression