Role of the amygdala

• Structure & function of amygdala:

  Made of, 'grey matter': collection of neuron cell bodies densely packed together into a cluster of 13 nuclei. Located in medial temporal lobe of brain & is part of limbic system. 1 amygdala in each hemisphere. Highly connected- neurally linked to hypothalamus, hippocampus, prefrontal cortex & other parts of brain. Widespread influence on brain functioning & behaviours associated with emotion, motivation & social interaction. Major role in how we assess & respond to environmental threats, so important in determining aggressive behaviour.
• Papez (1937) & Maclean (1952)


  Amygdala first implicated in emotional behaviour by them.
• Coccaro et al (2007)


  Investigated effects of amygdala on aggression by studying those with IED (intermittent explosive disorder)-common symptom=outbursts of reactive aggression. Each participant viewed images of faces at same time as having fMRI scans of their brains. Those with IED showed high levels of amygdala activity when viewing angry faces compared to non-IED controls. Association between amygdala activity & processing of aggressive emotions. Study had high realism as angry facial expression is an everyday signal of threat.
• Yu Gao et al (2010) mechanism:

  Proposed mechanism by which amygdala dysfunction affects aggression & criminal behaviour. We learn as kids to inhibit our aggressive & antisocial behaviours through fear conditioning-learn aggressive behaviour leads to punishment & negative outcomes. Amygdala involved in processing fear info & fear conditioning. Amygdala dysfunction= child can't identify social cues that indicate threat (e.g, angry faces) so doesn't link punishment to their aggressive behaviour. Fear conditioning disrupted so seems fearless, overly aggressive & antisocial.
• Yu Gao et al (2010) study:


  Longitudinal study- 1795 participants tested for fear conditioning at 3 years old. Measure used- physiological arousal indicated by sweating in response to painful noise. 20yrs later, found which participants involved in criminal behaviour. Those who'd committed crimes at age 23 had shown no fear conditioning at 3 years old. May be causal relationship between amygdala dysfunction & antisocial behaviour.
• Glenn et al (2009)


  Studied 17 participants with varying degrees of psychopathy. Underwent fMRI scans of their brains while making judgements about dilemmas. Association between psychopathy & reduced amygdala activity during decision-making in emotional moral dilemmas. Amygdala responds to signals of distress in others, so normal amygdala activity inhibits antisocial behaviour. Dysfunction in psychopaths means inhibitory mechanism disrupted, so able to make impulsive decisions, behave aggressively & involve in C.B without guilt.
• What is a central deficit in psychopathy?

  Amygdala dysfunction.
• What is psychopathy?

  One of, 'dark triad' of personality disorders, along with narcissism & Machiavellianism. Manipulative, emotionless, cunning, deceitful & severely lacking empathy. Amygdala dysfunction central deficit.
• Gospic et al (2011)


  Used, 'Ultimatum game'. Participants played role of responder whilst undergoing fMRI brain scans. When responders rejected unfair offers, amygdala activity heightened & quicker. Sedative drug given before game had 2 effects: reduced aggression(halved number of rejections)& at same time reduced amygdala activity. Association between reactive aggression and increased amygdala activity.
• What is the Ultimatum game?

  Lab-based method of measuring aggressive behaviour. 2 players(proposer & responder)& sum of money. Proposer offers to split money fairly or unfairly (unfair considered social provocation or threat). If responder accepts-money split accordingly. If responder rejects-both get nothing. Rejection of offer considered aggressive behaviour.
• Pardini et al (2014)


  Selected 503 males who'd been part of earlier study in 1986-1987 at 6/7 years old. 20 years later identified subgroup of 56 men who'd shown aggressive behaviour since childhood, including involvement in serious criminal violence (rape, robbery, etc). fMRI brain scans used to measure amygdala volume. Found high levels aggression over 20yr period associated with lower amygdala volumes. Association persisted in follow-up study 3yrs later.
• Evaluate Pardini et al (2014)

  Findings can't be explained by potential confounding variables (race, IQ, age) or by earlier levels of aggressive behaviour (all controlled in study). Differences in amygdala volumes may predict future aggressive behaviour and C.B.
• Raine et al (1997)


  Investigated murderers who'd used overwhelming degree of reactive aggression in crimes. Had greater activity in amygdala, but abnormally low metabolism in prefrontal cortex. Regulation of aggressive C.B is complex-involves at least 3 important brain structures: amygdala, OFC & neural connection between. Amygdala dysfunctions not enough to explain C.B (oversimplified). C.B outcome of many influences. Amygdala part of wider system of connected brain structures.
• What is the OFC?

  Orbitofrontal cortex in prefrontal cortex. Thought to influence self-control, regulate impulsive behaviour & inhibit aggression.
• Effects of amygdala are indirect

  Amygdala role in regulating fear-related behaviours. Damage to amygdala affects ability to process fear-related info normally-affects social functioning (reduced empathy). Makes aggressive behaviour more likely but not inevitable. Amygdala dysfunction may be risk factor for C.B. Cause of C.B more complex.
• What is genetic engineering?

  Genetic composition altered so undesirable traits eradicated. E.g, replace defective MAOA gene with normal one in fertilised ovum. Unsuccessful in past- eugenic movement in early 20th century advocated sterilisation of criminals & other undesirable people. Unethical, especially as Nazis gave support to idea.
• Gesch et al (2002)


  Conducted placebo-controlled, randomised, double-bind study with 231 adult British prisoners. Some given capsules containing nutrients, others given placebo. After 2 weeks, active intervention group committed 35% fewer disciplinary offences on average than they had before trial. Committed 26% fewer offences on average than placebo control group.