Aggression : Neural Mechanisms Flashcards
What is hot blooded aggression?
Impulsive behaviour coupled with physiological arousal. Eg: Tony Martin (1999) shot at 3 intruders, killed 1 16yo who had burgled his home. Initially sentenced to life, reduced to 3 years due to circumstances
What is cold blooded aggression?
Premeditated acts. Eg: The Moors Murders - lan Brady & Myra Hindley (1963-65) killed 5 children and buried the bodies in Saddleworth Moors
What is serotonin?
inhibitory neurotransmitter important in controlling/ calming aggressive impulse (slows neuronal activity)
What is 5-HTzA?
Serotonin subtype (S-Hydrox(trapamine) 2a – subtype of receptor)
Relationship between serotonin and aggression?
Reduced serotonin can lead to increased neuronal activity which leads to aggression.
What is D₂?
Dopamine receptor
What is the limbic system?
A set of neural structures located in the centre of the brain that processes emotional responses such as aggression. The amygdala and hypothalamus are key to aggressive responses.
What makes up the limbic (Papez circuit 1935)?
The amygdala, thalamus/ hypothalamus, hippocampus
Whats the amygdala’s role?
Linked to the production of aggressive behaviour (Gospic found fMRIs showed increased activity during aggressive responses)
What’s the hypothalamus’ role?
Integrates and expresses emotional responses (can trigger aggressive behaviour as a part of fight or flight)
Whats the orbital cortex’s role?
The external layer of the brain, controls executive function (decision making) which attempts to control aggression produced by the limbic system.
Kluver and Bucky (1937)
Discovered the destruction of the amygdala in a monkey dominant in a social group caused it to lose its dominance. The monkey immediately reached for the grape (normal reaction) then stated to play with and pet the rubber snake (unnatural reaction).
What is Kluver-Bucky syndrome?
Discovered the destruction of the amygdala in a monkey dominant in a social group caused it to lose its dominance. The monkey immediately reached for the grape (normal reaction) then stated to play with and pet the rubber snake (unnatural reaction).
Mark and Ervin (1970) and King (1961)
Woman receiving painless stimulation to amygdala became enraged and smashed her guitar against the wall. A woman being interviewed and having her amygdala stimulated experienced quick onset aggression (ripped up paper and self hatred for the aggressive thoughts), which quickly passed as the area was up stimulated.
Gospic at al (2011)
The Ultimate Game - Subject A is the Proposer, subject B is the Responder (subjected to mild provocovation). A has £100 and can split it any way between A and B. B gets to accept the offer or decline – where neither get the money. The researchers used fMRI to monitor brain activity while playing, and found that when B rejected the offer there was inc response in the amygdala. Also found that when the Ps took Benzodiazepines, (calm anxiety), it halved the number of rejections and decreased amygdala activity.
What are optogenetics?
By introducing light sensitive proteins into target cells, researchers can precisely activate or inhibit these cells with light pulses
Lin et al’s 2011 study
Used optogenetics to stimulate the hypothalamus to investigate its role in controlling aggression in male mice. Activation of this area caused aggressive behaviour (attacking other mice and inanimate objects). Inhibition of the hypothalamus caused the mice’s aggressive behaviors to stop. This provides direct evidence that the hypothalamus (receives connections from the amygdala) is a critical brain region for initiating and regulating aggression
Animal Studies evidence
pharmacologically blocking/ genetically modifying 5-HTzA receptors. Mice no gene responsible for 5-HTa expression show less aggressive behaviour vs typical mice. Stimulating 5-HTza can lead to aggression, especially when the animal perceives threat or competition
Anti-psychotics evidence
drugs for schizophrenia block the D₂ receptor, but some impact other receptors. Risperidone and olanzapine block 5-HTzA receptor, and reduce aggression in patients with schizophrenia or dementia
Serotonergic Metabolites evidence
Virkunnen et al (1994) 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, because the reduction of 5-H1AA means there is decreased serotonin activity in the brain which effects controlling impulsive (reactive) aggressive behaviour.
Serotonin-Depletion Studies evidence
Passamonti et al. (2012) used acute tryptophan depletion (ATD) to temporarily reduce serotonin (tryptophan is the precursor for serotonin). The results showed ATD reduced connectivity between the PFC and amygdala when participants viewed angry faces, suggesting low serotonin might impair PFC’s ability to regulate the amygdala’s response to aggression-related cues
Post-Mortem Studies evidence
Rosell and Siever (2015) reviewed post-mortem studies, indicating that individuals with histories of impulsive aggression or violent behavior often show an upregulation of 5-HTzA receptors (perhaps compensating for low serotonin) in the PFC, particularly in the orbitofrontal cortex.
What are the strengths of neural mechanisms?
- Studies in offenders suggest that abnormal activity in brain areas associated with emotional regulation may play a role in violent behaviour → Raine et al. (1997) used PET scans to compare limbic activity of individuals who’d committed murder by reason of insanity with non-murderers, finding reduced activity in limbic regions in the murderer group. However, murder due to insanity may not directly equate to directly aggression. A study by Coccaro et al. (2007) therefore provides important context, showing that patients with Intermittent Explosive Disorder (IED) exhibited reduced activity in the orbitofrontal cortex (OFC) and amygdala when shown angry faces.
- strength of the argument that the limbic system is involved in aggression comes from case study evidence that damage to the limbic system through trauma or disease can lead to aggressive behaviours → Burns & Swerdlow (2003) reported a case study in which pedophilia emerged following a tumour in the orbitofrontal cortex, which resolved after surgery. This demonstrates that disruption of the amygdala can lead to aggression and is supported by a similar case study reported by Sumer (2007) of a 14-year-old girl with extreme aggression was shown to be the result of a tumour pressing on her amygdala. Although there are problems with extrapolation.
- drugs research shows that increasing serotonin activity reduces aggressive behavior → Berman (2009) conducted a study where Ps got a placebo or a dose of paroxetine (a drug that increases serotonin activity). Ps then took part in a game where they administered shocks in response to provocation. Ps who received paroxetine consistently gave fewer and less intense shocks, particularly among those with a prior history of aggressive behavior
What are the limitations of neural mechanisms?
- much of it is correlational, which restricts our ability to establish causality → Correlational studies are necessary due to ethical constraints (directly provoking aggression in laboratory setting would cause harm). Researchers rely on brain scans to observe correlations between aggression and brain structures (eg: the amygdala or orbitofrontal cortex (OFC))
- lack of construct validity in the way aggression is operationalised as a dependent variable → In aggression studies, researchers measure aggressive responses through specific actions within controlled scenarios. Gospic et al. used the rejection of offers in the ultimatum game to show aggression, while Berman et al. (2009) gauged aggression through the delivery of electric shocks between Ps during a laboratory game.
