Biological theories of Aggression

Created by: euphoric-state
Created on: 07-06-15 18:52

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Biological Explanations of Aggression
- MAOA gene
  - Regulates enzyme of same name.
    - Enzyme mops up excess amounts of neurotransmitters.
      - Seratonin
        Build up can lead to aggressive response.
      - Dopamine
      - 2 activity forms
        High activity (H-MAOA)
        High levels of enzyme produce
        
        Low Activity (L-MAOA)
        Less enzyme produced
        Higher levels of aggression
  - Strengths
    - Cases et al
      - Genetically engineered mice -> lacking MAOA.
        Mice had dramatically altered serotonin
        Mice showed enhanced aggression esp. during mating
        t/f MAOA deficiency = aggressive behaviour
    - Mattson
      - MAOA def. MALE mice attacked new mice
        T/F effect may only be inherited by males
    - Brunner
      - Defective MAOA gene in Dutch family
        Males in fam = history of DV
        t/f defective MAOA gene does play a role in human aggression
        The fact that these studies show MAOA affects ag. in humans + animals provides strong evidence for the role of MAOA in aggression.
        T/F effect may only be inherited by males
        
        t/f MAOA deficiency = aggressive behaviour
  - Weaknesses
    - Moffit et al
      - Anti Social Behaviour = 9x more likely in L-MAOA ppts who had been abused
        Suggests that MAOA gene requires an enviromental trigger to be activated
    - Deneris et al
      - behaviour of GM mice w.out PET-1 gene = reminiscent of human psych disorders
        GM mice = not enough seretonin. t/f PET-1 is necessary for foetal development of those neurons
- Neural Mechanisms
  - Amygdala & PFC
    - PFC = regulation of correct social behaviour
      - Damage
        Impulsivity
        
        Immaturity
        
        Altered emotionality
    - Strengths
      - Potegal et al
        Stimulation of the corticomedial amygdala = aggressionn
        Lesioning the area = reduces aggression
        Supportive bc amygdala = inv. in aggressive behaviour.
        Research not done on humans
        Stimulation of the corticomedial amygdala = aggressionn
        Lesioning the area = reduces aggression
        Supportive bc amygdala = inv. in aggressive behaviour.
        Research not done on humans
      - Raine
        Significant differences/ lev. brain activity
        41 murderers & control group
        Lateral + Medial PFC = murderers - less activity
        Areas w/abnormal activity
        Lowered self control
        
        Increased aggression / impulsivity
        
        problems w/ controlling / expression of emotion
        
        Lack of fear
      - Volkow
        Reduced PFC activity in 9 psychiactric prisoners
    - IDA
      - Socially Sensetive research
        Wider ranging implications for society b/c lack of control
        Lack/control = issue of culpability
        Biology influences agg-prisoners = no blame
  - Serotonin
    - Reduces agg by inhibiting responses to emotional stimuli
      - Normal levels
        Calming, inhibitory effect
      - Low levels
        Reduces calming, inhibitory effect
    - Supporting Evidence
      - Mann et al
        dexfenfluramine - 35 healthy adults
        Dexfenflurmaine - depletes serotonin levels
        
        Questionnaire: assess hostility & agg
        Found: male hostility + agg increased post treatment
      - HOWEVER
        role/neurotransmitter = unclear
        low levels of serotonin -> agg DOESN'T FIT W/WARRIOR GENE RESEARCH
        Cases et al
        W/G disabled -> S levels INCREASED
        t/f may not be as simple as "high"/"low" levels of seretonin
  - Dopamine
    - response to rewarding stimuli
      - aggressive behaviour produces a rush of dopamine
        t/f pleasure
        bc aggression = pleasure, behaviour will be repeated.
      - food
      - sex
    - Supportive Evidence
      - Lavine
        Increased aggression
        When AMPHETAMINES administered.
      - Buitelaar
        Decreased aggression
        When DOPAMINE INHIBITING APs taken
        
        However
        doesn't tell us how dopamine is linked to aggression.
- Hormonal Mechanisms
  - Testosterone
    - Produced by the LEYDIG CELLS
      - Male testes
        10x more than females
        
        Muscle Growth
        
        Bone Growth
        
        Aggression
      - Adrenal Cortex
      - Female ovaries
    - Basal Model
      - Testosterone causes change in levels of DOMINANCE
        + testosterone = + competition & + dominance
        Dominance = aggression
    - Serotonogenic Synapses
      - low levels serotonin = high levels of aggression
        T modulates certain neurotransmitters that lead to + levels of aggression
    - Supportive Evidence
      - Beeman
        Castration decreases aggression
        Castrating male mice reduced their aggresion
        Normal levels re-established when injected w/testostrne
      - Edwards
        injections of T in F/Mice made them act like M/Mice w/increased T.
        Behaviours compared to control mice only given T as adults
        T masculinizes andro/sensetive circuitrs
        Explains why timing of castration = crucial
    - Weaknesses
      - Simpson
        T = implicated to only certain types of aggression
      - Albert
        Lots of research that shows no relationship between agg & T
      - IDA
        Nature & Nurture
        Enviroments facilitate aggression
        Feilden & Lutter
        ppts saliva tested for T before / after World Cup match
        Average T levels of WINNING fans increased by 27.6%
        Losing fans decreased by 26%
        
        This suggests some group situations increase levels of T, therefore social factors come into play
        Losing fans decreased by 26%

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Biological theories of Aggression

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